Twinning across the Developing World

Should singleton birth weight standards be applied to identify small-for-gestational age twins?: analysis of a retrospective cohort study

BACKGROUND

Twin birth weight percentiles are less popular in clinical management among twin pregnancies compared with singleton ones in China. This study aimed to compare the incidence and neonatal outcomes of small for gestational age (SGA) twins between the use of singleton and twin birth weight percentiles.

METHODS

This was a retrospective cohort study of 3,027 pregnancies with liveborn twin pairs at gestational age of > 28 weeks. The newborns were categorized as SGA when a birthweight was less than the 10th percentile based on the singleton and twin references derived from Chinese population. Logistic regression models with generalized estimated equation (GEE) were utilized to evaluate the association between SGA twins and neonatal outcomes including neonatal unit admission, neonatal jaundice, neonatal respiratory distress (NRDS), neonatal asphyxia, ventilator support, hypoxic ischemic encephalopathy (HIE), bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), intracranial hemorrhage (ICH), culture-proven sepsis, neonatal death within 28 days after birth as well as the composite outcome.

RESULTS

The incidence of SGA was 33.1 % based on the singleton reference and 7.3 % based on the twin reference. Both of SGA newborns defined by the singleton and twin references were associated with increases in neonatal unit admission, neonatal jaundice and ventilator support. In addition, SGA newborns defined by the twin reference were associated with increased rates of BPD (aOR, 2.61; 95 % CI: 1.18-5.78) as well as the severe composite outcome (aOR, 1.93; 95 % CI: 1.07-3.47).

CONCLUSIONS

The use of singleton birth weight percentiles may result in misdiagnosed SGA newborns in twin gestations and the twin birth weight percentiles would be more useful to identify those who are at risk of adverse outcomes.

The association between maternal and foetal factors with birth weight discordance in twins from Yucatan, Mexico

Birth weight discordance (BWD) is not an uncommon event in twin pregnancies and can be associated with maternal and newborn characteristics. We aimed to analyse the association between maternal sociodemographic and newborn characteristics with BWD in twin infants born in Yucatan, Mexico, during 2008-2017 (n = 2091 pairs). BWD was calculated as the percentage of birth weight of the heavier twin. We defined three categories of BWD: concordant twins: <15%, mild-discordant: 15-24%, and severe discordant: ≥25%. A multinomial logistic regression model was used to analyse the association between maternal sociodemographic and newborn characteristics with BWD. Seventy-four percent (n = 1547) of twin pairs were classified as concordant, 17% (n = 356) met the criteria for mild-discordance and 9% (n = 188) for severe discordance. The odds for mild-discordance were significantly lower for mothers with medium level of education and in the highest quartile of total twin birth weight (TBW). Opposite-sex twin pairs showed increased odds for mild-discordance compared with same-sex pairs. The odds for severe discordance increased as mothers were in older age groups and decreased as TBW increased. Our rates of BWD are similar to those reported in populations from wealthier countries and maternal age and education, infants' sex, and TBW are associated with BWD.

Perinatal Outcome of Selective Intrauterine Growth Restriction in Monochorionic Twins: Evaluation of a Retrospective Cohort in a Developing Country

Selective intrauterine growth restriction (sIUGR) in monochorionic twin pregnancies is associated with greater morbidity and mortality for both fetuses when compared to singleton and dichorionic pregnancies. This retrospective cohort study aimed to assess the perinatal outcomes of monochorionic twin pregnancies affected by this disorder and conducted expectantly, by analyzing the results according to the end-diastolic flow in the umbilical artery Doppler of the smaller twin (type I: persistently forward/type II: persistently absent or reversed/type III: intermittently absent or reversed). Seventy-five monochorionic diamniotic twin pregnancies with sIUGR were included in this study. sIUGR was defined by estimated fetal weight below the 3rd centile for gestational age, or below the 10th centile, when associated with at least one of the following three criteria: abdominal circumference below the 10th percentile, umbilical artery pulsatility index of the smaller twin above the 95th percentile, or estimated fetal weight discordance of 25% or more. Perinatal outcomes were analyzed from the prenatal period to hospital discharge and included perinatal death, neurological injury, retinopathy of prematurity (ROP), bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), and sepsis. The mortality rate was 1.33% in this cohort. The overall morbidity rate was lower in type I twin pregnancies. In conclusion, this study shows that sIUGR type I has lower morbidity than types II and III in expectant management.

Reared-apart/reared-together Chinese twins and virtual twins: Evolving research program and general intelligence findings

China's One-Child Policy (1979-2015) limited rural families to two children and urban families to one child. This practice, which led to the abandonment of hundreds of thousands of female infants, is indirectly responsible for the separate placement of infant twins. The availability of this sample launched the first prospective study of these pairs. Participants include families and twins comprising 15 monozygotic (MZA) pairs and 7 dizygotic (DZA) pairs from countries throughout the world. The research program is described, and the initial wave of IQ scores for MZA and DZA twin pairs is examined in the first comprehensive report from this study. The twins' mean age at participation was 9.41 years (SD = 6.36), and their ages ranged from 3.19 to 24.98 years. Informative contrasts with adopted-together Chinese twins and virtual twins (same-age unrelated individuals reared together) highlight shared genetic and environmental effects on intellectual development. Applied directions based on findings from these novel samples are described.

Associated factors with neonatal near miss in twin pregnancies in a public referral maternity unit in Brazil

Objective

The aim was to analyze the factors associated with neonatal near miss (NNM) in twin pregnancies in a public referral maternity unit in Brazil.

Material and Methods

This retrospective, cross-sectional study included 697 twin newborns. Cases of fetal and neonatal deaths were excluded. Neonates were divided into those meeting NNM criteria (5 min Apgar score <7, birth weight <1,500 g, gestational age at delivery <32 weeks, use of mechanical ventilation or congenital malformation, transfer before 28 days of life) and those who did not. In the bivariate analysis, the chi-square and Fisher's exact tests were used. Variables with a p-value ≤0.20 were subjected to the multiple analyses, which followed the Poisson regression model.

Results

The cohort consisted of 130 (18.7%) neonates meeting NNM criteria and 567 (81.3%) with no NNM criteria after multiple analyses, the following variables were associated with NNM: no previous pregnancy, prevalence ratio (PR): 1.38 [95% confidence interval (CI), 1.03-1.85]; >3 previous pregnancies, PR: 1.93 (95% CI, 1.38-2.69); premature rupture of membranes, PR: 1.50 (95% CI, 1.70-2.12); intrauterine growth restriction, PR: 2.28 (95% CI, 1.53-3.33); premature labor, PR: 1.63 (95% CI, 1.13-2.35); resuscitation in the delivery room, PR: 1.80 (95% CI, 1.24-2.62); and transfusion of blood products, PR: 4.44 (95% CI, 3.14-6.28).

Conclusion

The study findings indicate that having had 0 or >3 previous pregnancies, premature rupture of the membranes, intrauterine growth restriction, resuscitation in the delivery room, premature labor, and transfusion of blood products were associated with NNM in twin pregnancies.

Twin pregnancy and perinatal outcomes: Data from 'Birth in Brazil Study'

BACKGROUND

Twin pregnancies account for 0.5-2.0% of all gestations worldwide. They have a negative impact on perinatal health indicators, mainly owing to the increased risk for preterm birth. However, population-based data from low/middle income countries are limited. The current paper aims to understand the health risks of twins, compared to singletons, amongst late preterms and early terms.

METHODS

Data is from "Birth in Brazil", a national inquiry into childbirth care conducted in 2011/2012 in 266 maternity hospitals. We included women with a live birth or a stillborn, and excluded births of triplets or more, totalling 23,746 singletons and 554 twins. We used multiple logistic regressions and adjusted for potential confounders.

RESULTS

Twins accounted for 1.2% of gestations and 2.3% of newborns. They had higher prevalence of low birth weight and intrauterine growth restriction, when compared to singletons, in all gestational age groups, except in the very premature ones (<34 weeks). Amongst late preterm's, twins had higher odds of jaundice (OR 2.7, 95% CI 1.8-4.2) and antibiotic use (OR 1.8, 95% CI 1.1-3.2). Amongst early-terms, twins had higher odds of oxygen therapy (OR 2.7, 95% CI 1.3-5.9), admission to neonatal intensive care unit (OR 3.1, 95% CI 1.5-6.5), transient tachypnoea (OR 3.7, 95% CI 1.5-9.2), jaundice (OR 2.8, 95% CI 1.3-5.9) and antibiotic use (OR 2.2, 95% CI 1.14.9). In relation to birth order, the second-born infant had an elevated likelihood of jaundice, antibiotic use and oxygen therapy, than the first-born infant.

CONCLUSION

Although strongly mediated by gestational age, an independent risk remains for twins for most neonatal morbidities, when compared to singletons. These disadvantages seem to be more prominent in early-term newborns than in the late preterm ones.

Gestational Weight Gain and Its Effects on Maternal and Neonatal Outcome in Women With Twin Pregnancies: A Systematic Review and Meta-Analysis

Background: The incidence of twin pregnancies has risen recently. Such pregnancies are associated with an increased risk for poor maternal and infant outcomes. Gestational weight gain, particularly in singleton pregnancies, has been well-linked with maternal and infant outcomes. The aim of the current meta-analysis was to evaluate the effects of gestational weight gain on maternal and fetal outcomes in women with twin pregnancies. Methods: A systematic search was conducted using the PubMed, Scopus, and Google Scholar databases. Studies, either retrospective or prospective in design, evaluating the effects of gestational weight gain (defined using Institute of Medicine (IOM) guidelines) maternal and/or fetal/neonatal outcomes in women with twin pregnancies were included. Statistical analysis was performed using STATA software. Results: Eleven studies were included in the meta-analysis. Mothers with inadequate weight gain had increased risk for gestational diabetes mellitus (OR 1.19; 95% CI: 1.01, 1.40) and decreased risk for gestational hypertension (OR 0.58; 95% CI: 0.49, 0.68) and cesarean section (OR 0.94; 95% CI: 0.93, 0.96). Neonates born to mothers with inadequate weight gain were susceptible to increased risk for preterm delivery (OR 1.17; 95% CI: 1.03, 1.34), very preterm delivery (gestational age <32 weeks) (OR 1.84; 95% CI: 1.36, 2.48), small for gestational age status (OR 1.41; 95% CI: 1.15, 1.72), low birth weight status (<2,500 g) (OR 1.27; 95% CI: 1.17, 1.38), and neonatal intensive care unit (NICU) admission (OR 1.16; 95% CI: 1.08, 1.24). The pooled findings indicate an increased risk for gestational hypertension (OR 1.82; 95% CI: 1.60, 2.06) and cesarean section (OR 1.07; 95% CI: 1.05, 1.08) among mothers with excessive weight gain. Neonates born to mothers with excessive weight gain were susceptible to increased risk for preterm delivery and very preterm delivery, but were associated with a decreased risk for low birth weight status and small for gestational age status. Conclusions: Gestational weight gain in twin pregnancy, either lower or higher than IOM recommended guidelines, is associated with poor maternal and neonatal outcomes. Our findings call for incorporating counseling on optimal weight gain during pregnancy as part of routine antenatal visits.

Impact of SARS-CoV-2 on multiple gestation pregnancy

Objective

To assess clinical presentations, pregnancy complications, and maternal and neonatal outcomes among women with multiple gestation pregnancy (MGP) and confirmed SARS‐CoV‐2 (COVID‐19) infection and to compare the data with a pre‐pandemic period.

Methods

A retrospective study at a dedicated COVID‐19 Hospital in Mumbai, India. Data were obtained from the PregCovid Registry of pregnant and postpartum women with PCR‐confirmed SARS‐CoV‐2 infection from April to September, 2020. Data were also compared with a cohort of women with MGP attending the hospital pre‐pandemic (n = 63).

Results

Data from 879 women (singleton pregnancy, n = 859; MGP, n = 20) with COVID‐19 were assessed. The twinning rate was 34.2 per 1000 births. As compared with singleton pregnancies, a higher proportion of women with MGP and Covid‐19 delivered preterm (P = 0.001). Spontaneous abortions were also higher in the MGP group than in the singleton group (P = 0.055). The incidence of pre‐eclampsia/eclampsia was higher in the COVID‐19 MGP group than in both the COVID‐19 singleton (41.6% vs. 7.9%) and pre‐pandemic MGP (50.0% vs. 12.7%) groups.

Conclusion

There was a higher risk of pre‐eclampsia among women with MGP and COVID‐19. Women with MGP and COVID‐19 infection should receive special attention with a multidisciplinary approach to both maternal and neonatal care during the pandemic.

SARS‐CoV‐2 infection was found to be associated with increased risk of pre‐eclampsia and premature rapture of membranes among pregnant women with multiple gestation.

Multiple Gestations and Hypertensive Disorders of Pregnancy: What Do We Know?

PURPOSE OF REVIEW

The occurrence of hypertensive disorders of pregnancy (HDP) including gestational hypertension, chronic hypertension, preeclampsia, and eclampsia is proportional to the number of fetuses: singletons 6.5%, twins 12.7%, and triplets 20.0%. Literature on HDP in multifetal gestation is sparse compared with singletons. We aim to summarize the current evidence on HDP, specifically in twins.

RECENT FINDINGS

HDP occurs more frequently, at an earlier gestational age, and can present more severely and atypically in twin pregnancies. HDP in twins carries a higher risk of maternal/fetal morbidity and mortality including renal failure, stroke, cardiac arrest, pulmonary edema, placental abruption, cesarean delivery, fetal growth restriction, and iatrogenic preterm delivery. Low-dose aspirin (60-150 mg) should be initiated in all multifetal pregnancies to reduce the risk of preeclampsia. To improve outcomes and reduce inherent risks associated with multiple gestations, twins should be managed as high-risk pregnancies, and different from singletons.

Impact of growth discordance in twins on preeclampsia based on chorionicity

BACKGROUND

Despite extensive investigations over the last decade, preeclampsia remains an unpredictable pregnancy complication causing perinatal morbidity and mortality worldwide, particularly in twin pregnancies.

OBJECTIVE

This study aimed to determine the relationship between growth discordance in twin pregnancies and the risk for preeclampsia based on chorionicity.

STUDY DESIGN

This was a retrospective single-center study that included 2122 women with twin pregnancies who were admitted to a tertiary hospital between January 2013 and June 2016. Growth discordance was defined as twin birthweight difference ≥20%. Logistic regression models were used to analyze the association between growth discordance and risk for gestational hypertension-preeclampsia in all subjects. Stratified sampling by twin chorionicity (dichorionic and monochorionic) was also conducted. Further analysis was performed to estimate the association between the degree of growth discordance and gestational hypertension-preeclampsia risk in monochorionic and dichorionic twin pregnancies.

RESULTS

The prevalence of growth discordance was 17.6%. In all subjects, growth discordance was associated with increased risk for gestational hypertension-preeclampsia. After stratification by twin chorionicity, growth discordance was associated with an increased risk for gestational hypertension preeclampsia (adjusted odds ratio [AOR], 1.84; 95% confidence interval [CI], 1.26-2.67) and preeclampsia (AOR, 1.82; 95% CI, 1.21-2.73), including mild preeclampsia (AOR, 1.86; 95% CI, 1.02-3.37), severe preeclampsia (AOR, 1.78; 95% CI, 1.06-2.97; P<.05), and early-onset preeclampsia (AOR, 2.98; 95% CI, 1.40-6.32), in the dichorionic twin pregnancy group; however, no significant association was found in the monochorionic twin pregnancy group. A 10% increment of growth discordance in the dichorionic twin pregnancy group was associated with an elevated risk for gestational hypertension preeclampsia (AOR, 1.20; 95% CI, 1.02-1.41) and preeclampsia (AOR, 1.24; 95% CI, 1.04-1.48), including severe preeclampsia (AOR, 1.28; 95% CI, 1.04-1.59) and early-onset preeclampsia (AOR, 1.47; 95% CI, 1.08-2.00), but no significant association was found in the monochorionic twin pregnancy group.

CONCLUSION

Growth discordance is associated with an increased risk for preeclampsia in dichorionic but not in monochorionic twin pregnancy. In addition, the prevalence of preeclampsia increases significantly with increasing degree of growth discordance, reflecting a dose-response relationship in dichorionic twin pregnancy.

Gender Discrimination and Excess Female Under-5 Mortality in India: A New Perspective Using Mixed-Sex Twins

Son preference has been linked to excess female under-5 mortality in India, and considerable literature has explored whether parents invest more resources in sons relative to daughters—which we refer to as explicit discrimination—leading to girls’ poorer health status and, consequently, higher mortality. However, this literature has not adequately controlled for the implicit discrimination processes that sort girls into different types of families (e.g., larger) and at earlier parities. To better address the endogeneity associated with implicit discrimination processes, we explore the association between child sex and postneonatal under-5 mortality using a sample of mixed-sex twins from four waves of the Indian National Family Health Survey. Mixed-sex twins provide a natural experiment that exogenously assigns a boy and a girl to families at the same time, thus controlling for selectivity into having an unwanted female child. We document a sizable impact of explicit discrimination on girls’ excess mortality in India, particularly compared with a placebo analysis in sub-Saharan Africa, where girls have a survival advantage. We also show that explicit discrimination weakened for birth cohorts after the mid-1990s, especially in northern India, but further weakening has stalled since the mid-2000s, thus contributing to understandings of how the micro-processes underlying the female mortality disadvantage have changed over time.

Applying the Robson classification to routine facility data to understand the Caesarean section practice in conflict settings of South Kivu, eastern DR Congo

INTRODUCTION

Sub-Saharan Africa has low Caesarean (CS) levels, despite a global increase in CS use. In conflict settings, the pattern of CS use is unclear because of scanty data. We aimed to examine the opportunity of using routine facility data to describe the CS use in conflict settings.

METHODS

We conducted a facility-based cross-sectional study in 8 health zones (HZ) of South Kivu province in eastern DR Congo. We reviewed patient hospital records, maternity registers and operative protocol books, from January to December 2018. Data on direct conflict fatalities were obtained from the Uppsala Conflict Data Program. Based on conflict intensity and chronicity (expressed as a 6-year cumulative conflict death rate), HZ were classified as unstable (higher conflict death rate), intermediate and stable (lower conflict death rate). To describe the Caesarean section practice, we used the Robson classification system. Based on parity, history of previous CS, onset of labour, foetal lie and presentation, number of neonates and gestational age, the Robson classification categorises deliveries into 10 mutually exclusive groups. We performed a descriptive analysis of the relative contribution of each Robson group to the overall CS rate in the conflict stratum.

RESULTS

Among the 29,600 deliveries reported by health facilities, 5,520 (18.6%) were by CS; 5,325 (96.5%) records were reviewed, of which 2,883 (54.1%) could be classified. The overall estimated population CS rate was 6.9%. The proportion of health facility deliveries that occurred in secondary hospitals was much smaller in unstable health zones (22.4%) than in intermediate (40.25) or stable health zones (43.0%). Robson groups 5 (previous CS, single cephalic, ≥ 37 weeks), 1 (nulliparous, single cephalic, ≥ 37 weeks, spontaneous labour) and 3 (multiparous, no previous CS, single cephalic, ≥ 37 weeks, spontaneous labour) were the leading contributors to the overall CS rate; and represented 75% of all CS deliveries. In unstable zones, previous CS (27.1%) and abnormal position of the fetus (breech, transverse lie, 3.3%) were much less frequent than in unstable and intermediate (44.3% and 6.0% respectively) and stable (46.7%and 6.2% respectively). Premature delivery and multiple pregnancy were more prominent Robson groups in unstable zones.

CONCLUSION

In South Kivu province, conflict exposure is linked with an uneven estimated CS rate at HZ level with at high-risks women in conflict affected settings likely to have lower access to CS compared to low-risk mothers in stable health zones.

Effectiveness of cervical pessary compared to cervical cerclage with or without vaginal progesterone for the prevention of preterm birth in women with twin pregnancies and a short cervix: study protocol for a two-by-two factorial randomised clinical trial

INTRODUCTION

Women with twin pregnancies and a short cervix are at increased risk for preterm birth (PTB). Given the burden of prematurity and its attendant risks, the quest for effective interventions in twins has been an area of considerable research. Studies investigating the effectiveness of cervical cerclage, cervical pessary and vaginal progesterone in preventing PTB have yielded conflicting results. The aim of this study is to compare the effectiveness of cervical pessary and cervical cerclage with or without vaginal progesterone to prevent PTB in women with twin pregnancies and a cervical length (CL) ≤ 28 mm.

METHODS AND ANALYSIS

This multicentre, randomised clinical trial will be conducted at My Duc Hospital and My Duc Phu Nhuan Hospital, Vietnam. Asymptomatic women with twin pregnancies and a CL ≤28 mm, measured at 16-22 weeks' gestation, will be randomised in a 1:1:1:1 ratio to receive a cerclage, pessary, cerclage plus progesterone or pessary plus progesterone. Primary outcome will be PTB <34 weeks. Secondary outcomes will be maternal and neonatal complications. We preplanned a subgroup analysis according to CL from all women after randomisation and divided into four quartiles. Analysis will be conducted on an intention-to-treat basis. The rate of PTB <34 weeks' gestation in women with twin pregnancies and a cervix ≤28 mm and treated with pessary in our previous study at My Duc Hospital was 24.2%. A sample size of 340 women will be required to show or refute that cervical cerclage decreases the rate of PTB <34 weeks by 50% compared with pessary (from 24.2% to 12.1%, α level 0.05, power 80%, 5% lost to follow-up and protocol deviation). This study is not to be powered to assess interactions between interventions.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Institutional Ethics Committee of My Duc Hospital and informed patient consent was obtained before study enrolment. Results of the study will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT03863613 (date of registration: 4 March 2019).

Risk factors of unsuccessful vaginal twin delivery

INTRODUCTION

Twin trial of labor presents a challenge to obstetricians, as it is associated with a greater number of adverse birth outcomes compared with singleton deliveries. The risk of poor outcome has shown to be highest with unsuccessful vaginal twin delivery. The purpose of this study was to identify the clinical risk factors associated with intrapartum cesarean section in late preterm and term twin births.

MATERIAL AND METHODS

All live diamniotic twin deliveries of at least 35⁺⁰ weeks of gestation with planned vaginal delivery were included in this retrospective single-center cohort study. Maternal and newborn characteristics were compared between a vaginal delivery group and an intrapartum cesarean section group. Logistic regression analysis was carried out to determine independent risk factors of intrapartum cesarean section. Further, maternal and neonatal outcomes were compared between groups of vaginal delivery and cesarean section for both twins and also between groups of vaginal delivery and cesarean section for the second twin only (combined delivery). The impact of presentation of the second twin on the mode of twin delivery and on neonatal outcome was also examined.

RESULTS

Among 821 twin pregnancies, 581 mothers (70.8%) attempted trial of labor and were eligible for the study. With a cephalic-presenting first twin, the trial of labor rate was 89.3% and vaginal delivery was successful in 82.8%. Nulliparity (odds ratio [OR] 3.2, 95% confidence interval [CI] 2.0-5.1) and non-cephalic presentation of the second twin (OR 3.0, 95% CI 1.9-4.8) were found to be independent risk factors of cesarean section. However, 76.1% of mothers with non-cephalic second twins achieved vaginal delivery and perinatal outcomes were comparable with cases of cephalic-presenting second twins. When comparing delivery modes, maternal outcomes were more favorable with vaginal delivery, whereas combined delivery increased the second twin's risk of adverse neonatal outcome.

CONCLUSIONS

This study, with high rates of trial of labor and successful vaginal twin delivery, found nulliparity and non-cephalic presentation of the second twin to be risk factors of intrapartum cesarean section in twin pregnancies.

Exclusive Breastfeeding and Associated Factors among Mothers with Twins in the Tamale Metropolis

BACKGROUND

Exclusive breastfeeding (EBF) for the first six months after birth has been recommended by the WHO as the best infant feeding strategy. Data on EBF rates among twin infants in Ghana remain limited and for that matter hypothesized to be low.

AIM

The study sought to measure the prevalence of EBF and identify associated factors among twins in the Tamale metropolis.

METHODS

A cross-sectional survey involving 185 mother-twin pairs was conducted in four health facilities in the Tamale metropolis providing Child welfare Clinic (CWC) services. Socio-demographics data on both mother and twin were taken. Biomedical (e.g. perceived onset of lactation, confidence of producing enough milk, parity, delivery place, delivery type, time of breastfeeding initiation) and bio cultural factors (e.g. family cooperation for current infant feeding, breastfeeding counselling) were also obtained. In-depth interviews were also conducted with a sub sample of mothers (30) who were purposively selected to generate qualitative data on breastfeeding and associated cultural factors in twins as this data was necessary to aid in the explanation of the quantitative results.

RESULTS

Only 17% of twin infants were exclusively breastfed for six months. Women who were not confident that they could produce enough breast milk were about 83% less likely to practice exclusive breast-feeding (EBF) compared to those who were confident that they could produce enough breast milk (AOR = 0.17; CI = 0.04, 0.73; p-value = 0.017). Moreover, mothers who had no access to radio were about 87% less likely to practice EBF (AOR = 0.13; CI = 0.02, 0.79; p-value = 0.017). Moreover, mothers who had no access to radio were about 87% less likely to practice EBF (AOR = 0.13; CI = 0.02, 0.79.

CONCLUSIONS

The study shows that, ownership of radio, confidence of producing enough breast milk and admission of the children into NICU were identified as the most important factors affecting exclusive breastfeeding of twins. Beyond Educating, encouraging and assuring twin mothers of their abilities to produce enough breast milk to satisfy their children, healthcare professionals should pay more attention on providing appropriate information on breastfeeding to mothers and caregivers.

The Nigerian Twin and Sibling Registry: An Update

Here we provide an update of the 2013 report on the Nigerian Twin and Sibling Registry (NTSR). The major aim of the NTSR is to understand genetic and environmental influences and their interplay in psychological and mental health development in Nigerian children and adolescents. Africans have the highest twin birth rates among all human populations, and Nigeria is the most populous country in Africa. Due to its combination of large population and high twin birth rates, Nigeria has one of the largest twin populations in the world. In this article, we provide current updates on the NTSR samples recruited, recruitment procedures, zygosity assessment and findings emerging from the NTSR.

The Swedish Twin Registry: Content and Management as a Research Infrastructure

The Swedish Twin Registry functions as research infrastructure containing information on 216,258 twins born between 1886 and 2015, of whom 86,199 pairs have zygosity determined by DNA, an intrapair similarity algorithm, or being of opposite sex. In essence, practically all twins alive and currently 9 years or older have been invited for participation and donation of DNA on which genomewide single nucleotide polymorphisms array genotyping has been performed. Content, management and alternatives for future improvements are discussed.

A Computer-Based Tool for the Assessment of Voice Quality Through Visual Analogue Scales: VAS-Simplified Vocal Profile Analysis

In this study we propose a new tool for the perceptual assessment of voice quality. For its design, we have adapted the Simplified Vocal Profile Analysis so that the new tool features two main characteristics: (1) the ordinal scalar degrees of the original protocol are turned into a visual analog scale; and (2) the original paper-based version of the protocol is now a computer-based implementation. In order to assess the reliability of the new tool, five phoneticians listened to 12 different speakers and evaluated their voice quality using the proposed tool. Inter-rater agreement was then calculated using the Intraclass Correlation Coefficient. The results show that high agreement was reached for most of the perceptual settings of the protocol. Yet more investigations seem necessary into the continuous nature of the perceptual dimensions making up the voice quality of a speaker. As a preliminary approach to the graphical possibilities that the visual analog scale offers to the Simplified Vocal Profile Analysis, we explore the usefulness of multiple dot plots and propose an adaptation of the Bland-Altman plot to be used in pairwise comparisons. In this study, these visualization techniques are tested on two pairs of identical twins.

Genotyping of STR and DIP-STR Markers in Plasma Cell-Free DNA for Simple and Rapid Noninvasive Prenatal Diagnosis of Zygosity of Twin Pregnancies

Due to the high rate of complications, special medical care must be provided especially for monozygotic twin pregnancies, which are characterized as having 2.5 times higher mortality of fetuses. In recent years, examination of cell-free DNA (cfDNA) circulating in maternal plasma has become a useful noninvasive method of prenatal diagnosis. However, fetal DNA constitutes only 3-20% of plasma cfDNA during pregnancy. Short tandem repeats (STRs) are routinely used in forensic examination of DNA mixtures and are able to identify 5% minority components. Haplotypes of deletion/insertion polymorphisms and STRs (DIP-STRs) are able to detect even 0.1% minority components of DNA mixtures. Thus, STRs and DIP-STRs seem to be a perfect tool for detection of fetal alleles in DNA isolated from maternal plasma. Here, we present a novel noninvasive prenatal diagnosis technique of determination of pregnancy zygosity based on examination of feto-maternal microchimerism of plasma cfDNA with the use of STRs and DIP-STRs. Our preliminary results based on 22 STR loci showed 67% sensitivity, 100% specificity and 82% accuracy for prenatal detection of twin dizygosity. The corresponding values for seven DIP-STRs were 13%, 100% and 54%, respectively. Owing to assay performance, low DNA input requirements, low costs (below 10 USD per patient) and simplicity of analysis, genotyping of STR/DIP-STR markers in maternal plasma cfDNA may become a useful supplementary test for noninvasive prenatal diagnosis of twin zygosity in cases when chorionicity and zygosity cannot be reliably determined by ultrasound examination and prognostic value may be provided by a DNA test determining pregnancy zygosity.

Are preterm birth and intra-uterine growth restriction more common in Western Australian children of immigrant backgrounds? A population based data linkage study

Background

To compare the prevalence of preterm birth, post term birth, intra-uterine growth restriction and distribution of Apgar scores in offspring of foreign-born women in Western Australia with that of their Australian-born non-Indigenous and Indigenous counterparts.

Methods

A population-based linked data study, involving 767,623 singleton births in Western Australia between 1980 and 2010 was undertaken. Neonatal outcomes included preterm birth, post term births, intra-uterine growth restriction (assessed using the proportion of optimal birth weight) and low Apgar scores. These were compared amongst foreign-born women from low, lower-middle, upper middle and high income countries and Australian-born non-Indigenous and Indigenous women over two different time periods using multinomial logistic regression adjusted for covariates.

Results

Compared with Australian born non-Indigenous women, foreign-born women from low income countries were at some increased risk of extreme preterm (aRRR 1.59, 95% CI 0.87, 2.89) and very early preterm (aRRR 1.63, 95% CI 0.92, 2.89) births during the period from 1980 to 1996. During the period from 1997 to 2010 they were also at some risk of extreme preterm (aRRR 1.42, 95% CI 0.98, 2.04) very early preterm (aRRR 1.34, 95% CI 1.11, 1.62) and post term birth (aRRR 1.93, 95% CI 0.99, 3.78). During this second time period, other adverse outcomes for children of foreign-born women from low income and middle income countries included increases in severe (aRRR 1.69, 95% CI 1.30, 2.20; aRRR 1.72, 95% CI 1.53, 1.93), moderate (aRRR 1.54, 95% CI 1.32, 1.81; aRRR 1.59, 95% CI 1.48, 1.70) and mild (aRRR 1.28, 95% CI 1.14, 1.43; aRRR 1.31, 95% CI 1.25, 1.38) IUGR compared to children of Australian-born non-Indigenous mothers. Uniformly higher risks of adverse outcomes were also demonstrated for infants of Indigenous mothers.

Conclusions

Our findings illustrate the vulnerabilities of children born to foreign women from low and middle-income countries. The need for exploratory research examining mechanisms contributing to poorer birth outcomes following resettlement in a developed nation is highlighted. There is also a need to develop targeted interventions to improve outcomes for these women and their families.

Electronic supplementary material

The online version of this article (10.1186/s12884-019-2437-x) contains supplementary material, which is available to authorized users.

Maternal reproductive history: trends and inequalities in four population-based birth cohorts in Pelotas, Brazil, 1982-2015

Background

Brazil experienced important progress in maternal and child health in recent decades. We aimed at describing secular trends as well as socioeconomic and ethnic inequalities in reproductive history indicators (birth spacing, previous adverse perinatal outcome, parity and multiple births) over a 33-year span.

Methods

Four population-based birth cohort studies included all hospital births in 1982, 1993, 2004 and 2015 in Pelotas, Southern Brazil. Information on reproductive history was collected through interviews. Indicators were stratified by family income quintiles and skin colour. Absolute and relative measures of inequality were calculated.

Results

From 1982 to 2015, the proportion of primiparae increased from 39.2% to 49.6%, and median birth interval increased by 23.2 months. Poor women were more likely to report short intervals and higher parity, although reductions were observed in all income and ethnic groups. History of previous low birthweight was inversely related to income and increased by 7.7% points (pp) over time—more rapidly in the richest (12.1 pp) than in the poorest quintile (0.4 pp). Multiple births increased from 1.7% to 2.7%, with the highest increase observed among the richest quintile and for white women (220% and 70% increase, respectively). Absolute and relative income and ethnic-related inequalities for short birth intervals increased, whereas inequalities for previous low birthweight decreased over time.

Conclusions

In this 33-year period there were increases in birth intervals, multiple births and reports of previous low-birthweight infants. These trends may be explained by increased family planning coverage, assisted reproduction and a rise in preterm births, respectively. Our results show that socioeconomic and ethnic inequalities in health are dynamic and vary over time, within the same location.

Genetic Similarity Assessment of Twin-Family Populations by Custom-Designed Genotyping Array

Twin registries often take part in large collaborative projects and are major contributors to genome-wide association (GWA) meta-analysis studies. In this article, we describe genotyping of twin-family populations from Australia, the Midwestern USA (Avera Twin Register), the Netherlands (Netherlands Twin Register), as well as a sample of mothers of twins from Nigeria to assess the extent, if any, of genetic differences between them. Genotyping in all cohorts was done using a custom-designed Illumina Global Screening Array (GSA), optimized to improve imputation quality for population-specific GWA studies. We investigated the degree of genetic similarity between the populations using several measures of population variation with genotype data generated from the GSA. Visualization of principal component analysis (PCA) revealed that the Australian, Dutch and Midwestern American populations exhibit negligible interpopulation stratification when compared to each other, to a reference European population and to globally distant populations. Estimations of fixation indices (FST values) between the Australian, Midwestern American and Netherlands populations suggest minimal genetic differentiation compared to the estimates between each population and a genetically distinct cohort (i.e., samples from Nigeria genotyped on GSA). Thus, results from this study demonstrate that genotype data from the Australian, Dutch and Midwestern American twin-family populations can be reasonably combined for joint-genetic analysis.

Twin births in Jordan: incidence, trends, risk factors and implications for under-five mortality: evidence from the 2012 Jordan Population and Family Health Survey

Research on twinning in developed countries is well documented, but little is known about twinning in less-developed countries due to a lack of data or data limitations. This study examined the level of, trends in and determinants of twin births and their survival under age five in Jordan, using the 2012 Jordan Population and Family Health Survey (JPFHS) data. The birth history of 11,352 women included in the JPFHS provided information on 9859 live births that occurred within five years of the survey date, and these constituted the study subjects. Descriptive statistics, and bivariate and multivariate multilevel logistic regression models were used for data analysis. About 3.5% of the total live births were twins, which is one of the highest rates in developing countries. The twinning rate showed an increasing trend in Jordan, increasing by 45% from 2.4% in 1990 to 3.5% in 2012. Higher maternal age at child birth, higher parity, poor and richer economic status, contraceptive use status, secondary and above level of education of mothers and non-consanguinity were found to be associated with a higher rate of twin births in Jordan. Twins were observed to have a higher risk of low birth weight, being smaller in physical size at birth and at more than four times higher risk of neonatal death compared with singletons. To reduce the risk adverse outcomes of twin pregnancies and further improve maternal and child health, antenatal, delivery and postnatal care should be tailored towards the special needs of twin pregnancies and twin births in Jordan Twin pregnancies should be detected at the early stage of pregnancy so that perinatal outcomes can be improved by frequent prenatal visits, health education, counselling and proper management of peripartum complications.

The University of São Paulo Twin Panel: Current Status and Prospects for Brazilian Twin Studies in Behavioral Research

The University of São Paulo Twin Panel (Painel USP de Gêmeos), based at the Institute of Psychology of the University of São Paulo, started formally in 2017. Our registry is new, but in only two years of formal existence, it comprises a volunteer sample of 4826 registered individuals (98% twins and 2% higher-order multiples), recruited at the University of São Paulo and by social media campaigns. Our main aim is to conduct and promote research with twins on psychological processes and behavior. The University of São Paulo is the largest higher education and research institution in South America, and the Painel USP de Gêmeos has great potential for fostering research on twin-related issues from a psychological perspective in Brazil and South America.

Excess Infant Mortality of Twins Over Singletons in Arab Countries: The Evidence of Relative Survival Methods

There are no studies and only limited data that compare the difference in mortality between twins and singletons in the Arab world. We studied the survival of 306,966 children, including 9,280 twins, over the period 1970-2013 in six Arab countries (Algeria, Egypt, Iraq, Mauritania, Sudan and Tunisia) based on the Multiple Indicator Cluster Survey (MICS) database. With the use of relative survival models, we estimated the mortality of twins relative to singletons by including socioeconomic and demographic variables. This study confirms the results of previous studies on the excess risk of death of twins compared to singletons. There is evidence that excess mortality decreases with follow-up; in addition, male twins have a higher risk of death compared to females for all countries except Tunisia. Wealth index and education levels of women are factors that influence the risk of mortality. It is recommended that these findings are considered when performing future health and population strategies in these Arab countries.

A cost-effectiveness analysis of freeze-only or fresh embryo transfer in IVF of non-PCOS women

STUDY QUESTION

Is a freeze-only strategy more cost-effective from a patient perspective than fresh embryo transfer (ET) after one completed In Vitro Fertilization/ Intracytoplasmic Sperm Injection (IVF/ICSI) cycle in women without polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

There is a low probability of the freeze-only strategy being cost-effective over the fresh ET strategy for non-PCOS women undergoing IVF/ICSI.

WHAT IS KNOWN ALREADY

Conventionally, IVF embryos are transferred in the same cycle in which oocytes are collected, while any remaining embryos are frozen and stored. We recently evaluated the effectiveness of a freeze-only strategy compared with a fresh ET strategy in a randomized controlled trial (RCT). There was no difference in live birth rate between the two strategies.

STUDY DESIGN, SIZE, DURATION

A cost-effectiveness analysis (CEA) was performed alongside the RCT to compare a freeze-only strategy with a fresh ET strategy in non-PCOS women undergoing IVF/ICSI. The effectiveness measure for the CEA was the live birth rate. Data on the IVF procedure, pregnancy outcomes and complications were collected from chart review; additional information was obtained using patient questionnaires, by telephone.

PARTICIPANTS/MATERIALS, SETTING, METHODS

For all patients, we measured the direct medical costs relating to treatment (cryopreservation, pregnancy follow-up, delivery), direct non-medical costs (travel, accommodation) and indirect costs (income lost). The direct cost data were calculated from resources obtained from patient records and prices were applied based on a micro-costing approach. Indirect costs were calculated based on responses to the questionnaire. Patients were followed until all embryos obtained from a single controlled ovarian hyperstimulation cycle were used or a live birth was achieved. The incremental cost-effectiveness ratio (ICER) was based on the incremental cost per couple and the incremental live birth rate of the freeze-only strategy compared with the fresh ET strategy. Probabilistic sensitivity analysis (PSA) and a cost-effectiveness acceptability curve (CEAC) were also performed.

MAIN RESULTS AND THE ROLE OF CHANCE

Between June 2015 and April 2016, 782 couples were randomized to a freeze-only (n = 391) or a fresh ET strategy (n = 391). Baseline characteristics including mean age, Body Mass Index (BMI), anti-Mullerian hormone, total dose of Follicle Stimulating Hormone (FSH), number of oocytes obtained, good quality Day 3 embryos, fertility outcomes and treatment complications were comparable between the two groups. The live birth rate (48.6% vs. 47.3%, respectively; risk ratio, 1.03; 95% Confidence Interval [CI], 0.89, 1.19; P = 0.78) and the average cost per couple (3906 vs. 3512 EUR, respectively; absolute difference 393.6, 95% CI, -76.2, 863.5; P = 0.1) were similar in the freeze-only group versus fresh ET. Corresponding costs per live birth were 8037 EUR versus 7425 EUR in the freeze-only versus fresh ET group, respectively. The incremental cost for the freeze-only strategy compared with fresh ET was 30 997 EUR per 1% additional live birth rate. The direct non-medical costs and indirect costs of infertility treatment strategies represented ~45-52% of the total cost. PSA shows that the 95% CI of ICERs was -263 901 to 286 681 EUR. Out of 1000 simulations, 44% resulted in negative ICERs, including 13.0% of simulations in which the freeze-only strategy was dominant (more effective and less costly than fresh ET), and 31% of simulations in which the fresh embryo strategy was dominant. In the other 560 simulations with positive ICERs, the 95% CI of ICERs ranged from 2155 to 471 578 EUR. The CEAC shows that at a willingness to pay threshold of 300 000 EUR, the probability of the freeze-only strategy being cost-effective over the fresh ET strategy would be 58%.

LIMITATIONS, REASONS FOR CAUTION

Data were collected from a single private IVF center study in Vietnam where there is no public or insurance funding of IVF. Unit costs obtained might not be representative of other settings. Data obtained from secondary sources (medical records, financial and activity reports) could lack authenticity, and recall bias may have influenced questionnaire responses on which direct costs were based.

WIDER IMPLICATIONS OF THE FINDINGS

In non-PCOS women undergoing IVF/ICSI, the results suggested that the freeze-only strategy was not cost-effective compared with fresh ET from a patient perspective. These findings indicate that other factors could be more important in deciding whether to use a freeze-only versus fresh ET strategy in this patient group.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by My Duc Hospital; no external funding was received. Ben Willem J. Mol is supported by an NHMRC Practioner Fellowship (GNT 1082548) and reports consultancy for Merck, ObsEva and Guerbet. Robert J. Norman has shares in an IVF company and has received support from Merck and Ferring. All other authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

Not applicable.

Evidence that prenatal testosterone transfer from male twins reduces the fertility and socioeconomic success of their female co-twins

During sensitive periods in utero, gonadal steroids help organize biological sex differences in humans and other mammals. In litter-bearing species, chromosomal females passively exposed to prenatal testosterone from male littermates exhibit altered physical and behavioral traits as adults. The consequences of such effects are less well understood in humans, but recent near-doubling of twinning rates in many countries since 1980, secondary to advanced maternal age and increased reliance on in vitro fertilization, means that an increasing subset of females in many populations may be exposed to prenatal testosterone from their male co-twin. Here we use data on all births in Norway (n = 728,842, including 13,800 twins) between 1967 and 1978 to show that females exposed in utero to a male co-twin have a decreased probability of graduating from high school (15.2%), completing college (3.9%), and being married (11.7%), and have lower fertility (5.8%) and life-cycle earnings (8.6%). These relationships remain unchanged among the subsets of 583 and 239 females whose male co-twin died during the first postnatal year and first 28 days of life, respectively, supporting the interpretation that they are due primarily to prenatal exposure rather than to postnatal socialization effects of being raised with a male sibling. Our findings provide empirical evidence, using objectively measured nation-level data, that human females exposed prenatally to a male co-twin experience long-term changes in marriage, fertility, and human capital. These findings support the hypothesis of in utero testosterone transfer between twins, which is likely affecting a small but growing subset of females worldwide.

Biological insights into multiple birth: genetic findings from UK Biobank

The tendency to conceive spontaneous dizygotic (DZ) twins is a complex trait with important contributions from both environmental factors and genetic disposition. In earlier work, we identified the first two genes as maternal susceptibility loci for DZ twinning. The aim of this study was to identify genetic variants influencing multiple births and to genetically correlate the findings across a broad range of traits. We performed a genome-wide association study (GWAS) in 8962 participants with Caucasian ancestry from UK Biobank who reported being part of a multiple birth, and 409,591 singleton controls. We replicated the association between FSHB, SMAD3 and twinning in the gene-based (but not SNP-based) test, which had been established in previous genome-wide association analyses in mothers with dizygotic twin offspring. Additionally, we report a novel genetic variant associated with multiple birth, rs428022 at 15q23 (p = 2.84 × 10^-8) close to two genes: PIAS1 and SKOR1. Finally, we identified meaningful genetic correlations between being part of a multiple birth and other phenotypes (anthropometric traits, health-related traits, and fertility-related measures). The outcomes of this study provide important new insights into the genetic aetiology of multiple births and fertility, and open up novel directions for fertility and reproduction research.

National policies and care provision in pregnancy and childbirth for twins in Eastern and Southern Africa: A mixed-methods multi-country study

BACKGROUND

High-risk pregnancies, such as twin pregnancies, deserve particular attention as mortality is very high in this group. With a view to inform policy and national guidelines development for the Sustainable Development Goals, we reviewed national training materials, guidelines, and policies underpinning the provision of care in relation to twin pregnancies and assessed care provided to twins in 8 Eastern and Southern African countries: Kenya, Malawi, Mozambique, Rwanda, Tanzania, Uganda, Zambia, and Zimbabwe.

METHODS AND FINDINGS

We located policies and guidelines by reviewing national repositories and by contacting experts to systematically map country-level maternal and newborn training materials, guidelines, and policies. We extracted recommendations for care for twins spanning ante-, intra-, and postpartum care that typically should be offered during twin pregnancies and childbirth. We compared care provided for mothers of twins to that provided for mothers of singletons during the ante-, intra-, and postpartum period and computed neonatal mortality rates using the most recent Demographic and Health Surveys (DHS) data for each country. There was a paucity of guidance on care specifically for twin or multiple pregnancies: None of the countries provided clear guidance on additional number of antenatal care visits or specific antenatal content, while 7 of the 8 countries recommended twins to be delivered in a comprehensive emergency obstetric and neonatal care facility. These results were mirrored by DHS results of 73,462 live births (of which 1,360 were twin) indicating that twin pregnancies did not receive more frequent or intensified antenatal care. The percentage of twin deliveries in hospitals varied from 25.3% in Mozambique to 63.0% in Kenya, and women with twin deliveries were between 5 and 27 percentage points more likely to deliver in hospitals compared to women with singleton live births; this difference was significant in 5 of the 8 countries (t test p < 0.05). The percentage of twin deliveries by cesarean section varied from 9% in Mozambique to 36% in Rwanda. The newborn mortality rate among twins, adjusted for maternal age and parity, was 4.6 to 7.2 times higher for twins compared to singletons in all 8 countries.

CONCLUSIONS

Despite the limited sample size and the limited number of clinically relevant services evaluated, our study provided evidence that mothers of twins receive insufficient care and that mortality in twin newborns is very high in Eastern and Southern Africa. Most countries have insufficient guidelines for the care of twins. While our data do not allow us to make a causal link between insufficient guidelines and insufficient care, they call for an assessment and reconceptualisation of policies to reduce the unacceptably high mortality in twins in Eastern and Southern Africa.

Twinning Rates in Uruguay Between 1999 and 2015: Association with Socioeconomic and Demographic Factors

Twinning is rare among humans, but there is much variability among populations. Several studies show that certain demographic and socioeconomic factors, such as maternal age, mother's educational level and income, influence twinning rate. There is no background of analytical studies of twins in Uruguay. To the best of our knowledge, this is the first study that has focused on describing and analyzing Uruguayan twinning rates over a period of 17 years (1999-2015). The birth data were collected from the website of Uruguay's Ministry of Public Health. Economic data were obtained from Uruguay's Instituto Nacional de Estadísti's website for the period 2001-2013, since these variables are defined specifically for that period of time. The statistical software R (The R Project for Statistical Computing) was used. The twinning rate varied from 8.51 to 13 in the studied period. Montevideo has the highest median and the smallest variability in comparison with the other departments. In Uruguay (1999-2015), the highest twinning rate (28.94%) was observed in women aged 45 and older. The analysis also showed a relationship between twin birth rates and the mother's educational level. In three regions of the country (West, Center and East), twin births show a random pattern but in the other two (North and Metropolitan), there is an increasing trend in the number of twins over time. In conclusion, this study recognizes social, economic and demographic factors that influence in the rate of twin births in Uruguay.

Temporal trends in the birth rates and perinatal mortality of twins: A population-based study in China

OBJECTIVE

Until now, little was known about the epidemiological characteristics of twins in China due to a lack of reliable national data. In this study, we aimed to analyze temporal trends and perinatal mortality of twins from China.

METHODS

Data on twins between 2007 and 2014 were obtained from the China National Population-Based Birth Defects Surveillance System. Twin and singleton deliveries after at least 28 weeks of gestation were recruited and followed until postnatal day 42. Twinning rates were defined as the number of twin individuals per 1000 births(stillbirths and live births). The Weinberg's differential method was utilized to estimate the number of monozygotic and dizygotic twins.

RESULTS

During 2007-2014, the twinning rate increased by 32.3% from 16.4 to 21.7 per 1000 total births with an average of 18.8‰. Among twins, both the perinatal mortality rate (26.1 per 1000 total births) and neonatal death rate (15.7 per 1000 live births) presented a downward tendency but remained at a high level. Large urban-rural and geographic disparities were identified in twinning rates, in perinatal and neonatal mortality, and in their temporal trends.

CONCLUSIONS

The upward trend of twinning rates in China paired with the relatively high rates of perinatal and neonatal mortality among twins highlights the need for improved perinatal care in the light of socio-demographic differences.

Human Dizygotic Twinning: Evolutionary-Based Explanations/Twin Research Reviews: Conjoined Twins in a Triplet Pregnancy; Double Embryo Transfer; Health Anxiety; Delayed Delivery of the Second Twin/In the Media: Digital Marketing Twins; Bereaved Twin at March for Our Lives; Exchange of Places; Football Players Reunite as Patriots

Human twinning poses a conundrum for researchers, given that the female uterus is optimally designed to carry a single fetus. Evolutionary explanations of dizygotic (DZ or fraternal) twinning provide insight and understanding of this reproductive event. This review is followed by summaries of recent twin research and reports concerning twins in a triplet pregnancy, double embryo transfer; a twin study of health anxiety, and delayed delivery of the second twin. Twin events reported in the media include a pair of digital marketing twins, a speech by a bereaved twin at the March for Our Lives in Washington, D.C., twins who exchanged places, and a same-team reunion of twin football players.

Distinguishing genetically between the germlines of male monozygotic twins

Identification of the potential donor(s) of human germline-derived cells is an issue in many criminal investigations and in paternity testing. The experimental and statistical methodology necessary to work up such cases is well established but may be more challenging if monozygotic (MZ) twins are involved. Then, elaborate genome-wide searches are required for the detection of early somatic mutations that distinguish the cell sample and its donor from the other twin, usually relying upon reference material other than semen (e.g. saliva). The first such cases, involving either criminal sexual offenses or paternity disputes, have been processed successfully by Eurofins Genomics and Forensics Campus. However, when presenting the experimental results in court, common forensic genetic practice requires that the residual uncertainty about donorship is quantified in the form of a likelihood ratio (LR). Hence, we developed a general mathematical framework for LR calculation, presented herein, which allows quantification of the evidence in favour of the true donor in the respective cases, based upon observed DNA sequencing read counts.

In many instances of practical forensic casework, particularly when connected to sexual assault, genetic analysis is carried out to identify the likely donor of a sperm sample left at the crime scene. The experimental and statistical methodology for such investigations is well established. In cases involving monozygotic (MZ) twin suspects, however, the procedure is hampered by the fact that the two individuals usually coincide for the genetic markers tested. One way to overcome this problem is to use the latest DNA sequencing technology to undertake a genome-wide search for those few mutations that occur during early embryonic development and hence allow distinguishing between MZ twins in later life. Following this approach, the first cases of criminal sexual offense have been worked on successfully by Eurofins Genomics and Forensics Campus, leading to the identification of sperm sample donors from saliva reference samples taken from MZ twin suspects. As a matter of principle, however, the residual uncertainty of the experimental results needs to be evaluated and reported as well. Therefore, we developed a novel mathematical framework to quantify the evidential power of the genetic data in cases attempting to identify MZ twin donors, based upon comprehensive DNA sequencing. Moreover, we demonstrate that the same mathematical method can be used to resolve paternity disputes involving alleged fathers who have MZ twin brothers.

The Influence of Pentraxin 3 on the Ovarian Function and Its Impact on Fertility

Follicular development is a highly coordinated process that in humans takes more than 6 months. Pituitary gonadotropins and a variety of locally produced growth factors and cytokines are involved in determining a precise sequence of changes in cell metabolism, proliferation, vascularization, and matrix remodeling in order to obtain a follicle with full ovulatory and steroidogenic capability. A low-grade inflammation can alter such processes leading to premature arrest of follicular growth and female reproductive failure. On the other hand, factors that are involved in inflammatory response as well as in innate immunity are physiologically upregulated in the follicle at the final stage of maturation and play an essential role in ovulation and fertilization. The generation of pentraxin 3 (PTX3) deficient mice provided the first evidence that this humoral pattern recognition molecule of the innate immunity has a non-redundant role in female fertility. The expression, localization, and molecular interactions of PTX3 in the periovulatory follicle have been extensively studied in the last 10 years. In this review, we summarize findings demonstrating that PTX3 is synthesized before ovulation by cells surrounding the oocyte and actively participates in the organization of the hyaluronan-rich provisional matrix required for successful fertilization. Data in humans tend to confirm these findings, indicating PTX3 as a biomarker of oocyte quality. Moreover, we discuss the emerging evidence that in humans altered PTX3 systemic levels, determined by genetic variations and/or low-grade chronic inflammation, can also impact the growth and development of the follicle and affect the incidence of ovarian disorders.

Perinatal outcomes in twin pregnancies complicated by maternal morbidity: evidence from the WHO Multicountry Survey on Maternal and Newborn Health

Background

Twin pregnancy was associated with significantly higher rates of adverse neonatal and perinatal outcomes, especially for the second twin. In addition, the maternal complications (potentially life-threatening conditions-PLTC, maternal near miss-MNM, and maternal mortality-MM) are directly related to twin pregnancy and independently associated with adverse perinatal outcome. The objective of the preset study is to evaluate perinatal outcomes associated with twin pregnancies, stratified by severe maternal morbidity and order of birth.

Methods

Secondary analysis of the WHO Multicountry Survey on Maternal and Newborn Health (WHOMCS), a cross-sectional study implemented in 29 countries. Data from 8568 twin deliveries were compared with 308,127 singleton deliveries. The occurrence of adverse perinatal outcomes and maternal complications were assessed. Factors independently associated with adverse perinatal outcomes were reported with adjusted PR (Prevalence Ratio) and 95%CI.

Results

The occurrence of severe maternal morbidity and maternal death was significantly higher among twin compared to singleton pregnancies in all regions. Twin deliveries were associated with higher rates of preterm delivery (37.1%), Apgar scores less than 7 at 5th minute (7.8 and 10.1% respectively for first and second twins), low birth weight (53.2% for the first and 61.1% for the second twin), stillbirth (3.6% for the first and 5.7% for the second twin), early neonatal death (3.5% for the first and 5.2% for the second twin), admission to NICU (23.6% for the first and 29.3% for the second twin) and any adverse perinatal outcomes (67% for the first twin and 72.3% for the second). Outcomes were consistently worse for the second twin across all outcomes. Poisson multiple regression analysis identified several factors independently associated with an adverse perinatal outcome, including both maternal complications and twin pregnancy.

Conclusion

Twin pregnancy is significantly associated with severe maternal morbidity and with worse perinatal outcomes, especially for the second twin.

Diagnosing Zygosity in Giant Panda Twins Using Short Tandem Repeats

The giant panda, native to mountains of south-west China, is one of the world's rarest bear species and is subject to considerable conservation effort. In captivity, the proportion of twins accounts for 54% of the total number of births. To date, little is known about zygosity in panda populations - specifically, the proportion of monozygotic and dizygotic twins. In this study, we used 10 microsatellite markers for reliable zygosity testing, and the probability of monozygotic twins was 99.963% when all 10 markers were concordant. Out of 43 studied twin pairs, no MZ twins were found, indicating that there may be no identical panda twins (or the incidence is very low). We speculate that the fertilized eggs of giant pandas do not have the capability to split into two identical embryos, or that this ability is very poor, which is likely due to delayed implantation that is common in bear species. The results of this study deepen our understanding of giant panda breeding, yield insight into panda twins' likely mechanism of formation, and reduce the uncertainty of individual identity in wild population surveys.

Twin Peaks: A spatial and temporal study of twinning rates in Brazil

Twin births are an important public health issue due to health complications for both mother and children. While it is known that contemporary factors have drastically changed the epidemiology of twins in certain developed countries, in Brazil, relevant data are still scarce. Thus, we carried out a population-based study of live births in spatial and temporal dimensions using data from Brazil's Live Birth Information System, which covers the entire country. Over 41 million births registered between 2001 and 2014 were classified as singleton, twin or multiple. Twinning rates (TR) averaged 9.41 per 1,000 for the study period and a first-order autoregressive model of time-series analysis revealed a global upward trend over time; however, there were important regional differences. In fact, a Cluster and Outlier Analysis (Anselin Local Moran's I) was performed and identified clusters of high TR in an area stretching from the south of Brazil's Northeast Region to the South Region (Global Moran Index = 0.062, P < 0.001). Spearman's correlation coefficient and a Wilcoxon matched pairs test revealed a positive association between Human Development Index (HDI) and TRs in different scenarios, suggesting that the HDI might be an important indicator of childbearing age and assisted reproduction techniques in Brazil. Furthermore, there was a sharp increase of 26.42% in TR in women aged 45 and over during study period. The upward temporal trend in TRs is in line with recent observations from other countries, while the spatial analysis has revealed two very different realities within the same country. Our approach to TR using HDI as a proxy for underlying socioeconomic changes can be applied to other developing countries with regional inequalities resembling those found in Brazil.

Perinatal Mental Health Treatment Needs, Preferences, and Barriers in Parents of Multiples

PURPOSE

Many parents of multiples experience elevated mental health symptoms in the perinatal period. This population often presents with unique treatment needs and barriers to care; however, no tailored interventions have been developed for pregnant or postpartum mothers of multiples and/or their partners. This study involved an initial exploration of the perceived mental health treatment needs, preferences, and barriers to care in this population, as a first step toward developing such an intervention.

METHODS

Participants were 241 parents of multiples who were recruited in-person and online. They completed self-report measures assessing treatment history/preferences, barriers to care, and symptoms during the perinatal period.

RESULTS

Participants identified postpartum months 0 to 3 as the most difficult time. Few participants received any form of mental health treatment, although a significant percentage (approximately half) expressed interest in such treatment. Treatment interest was high for a range of clinical concerns. Participants were interested in both traditional treatment paradigms and eHealth approaches. Barriers to care were common, with the most common barrier being lack of time.

CONCLUSIONS

There is a large, unmet need for mental health treatment in parents of multiples in the perinatal period, especially the early postpartum months. eHealth strategies seem particularly feasible and acceptable in this population and may help circumvent common barriers to care. Clinical recommendations and considerations in treatment development are discussed.

Reducing early infant mortality in India: results of a prospective cohort of pregnant women using emergency medical services

OBJECTIVES

To describe the demographic characteristics and clinical outcomes of neonates born within 7 days of public ambulance transport to hospitals across five states in India.

DESIGN

Prospective observational study.

SETTING

Five Indian states using a centralised emergency medical services (EMS) agency that transported 3.1 million pregnant women in 2014.

PARTICIPANTS

Over 6 weeks in 2014, this study followed a convenience sample of 1431 neonates born to women using a public-private ambulance service for a 'pregnancy-related' problem. Initial calls were deemed 'pregnancy related' if categorised by EMS dispatchers as 'pregnancy', 'childbirth', 'miscarriage' or 'labour pains'. Interfacility transfers, patients absent on ambulance arrival, refusal of care and neonates born to women beyond 7 days of using the service were excluded.

MAIN OUTCOME MEASURES

death at 2, 7 and 42 days after delivery.

RESULTS

Among 1684 women, 1411 gave birth to 1431 newborns within 7 days of initial ambulance transport. Median maternal age at delivery was 23 years (IQR 21-25). Most mothers were from rural/tribal areas (92.5%) and lower social (79.9%) and economic status (69.9%). Follow-up rates at 2, 7 and 42 days were 99.8%, 99.3% and 94.1%, respectively. Cumulative mortality rates at 2, 7 and 42 days follow-up were 43, 53 and 62 per 1000 births, respectively. The perinatal mortality rate (PMR) was 53 per 1000. Preterm birth (OR 2.89, 95% CI 1.67 to 5.00), twin deliveries (OR 2.80, 95% CI 1.10 to 7.15) and caesarean section (OR 2.21, 95% CI 1.15 to 4.23) were the strongest predictors of mortality.

CONCLUSIONS

The perinatal mortality rate associated with this cohort of patients with high-acuity conditions of pregnancy was nearly two times the most recent rate for India as a whole (28 per 1000 births). EMS data have the potential to provide more robust estimates of PMR, reduce inequities in timely access to healthcare and increase facility-based care through service of marginalised populations.

Early neonatal mortality in twin pregnancy: Findings from 60 low- and middle-income countries

Background

Around the world, the incidence of multiple pregnancies reaches its peak in the Central African countries and often represents an increased risk of death for women and children because of higher rates of obstetrical complications and poor management skills in those countries. We sought to assess the association between twins and early neonatal mortality compared with singleton pregnancies. We also assessed the role of skilled birth attendant and mode of delivery on early neonatal mortality in twin pregnancies.

Methods

We conducted a secondary analysis of individual level data from 60 nationally-representative Demographic and Health Surveys including 521 867 singleton and 14 312 twin births. We investigated the occurrence of deaths within the first week of life in twins compared to singletons and the effect of place and attendance at birth; also, the role of caesarean sections against vaginal births was examined, globally and after countries stratification per caesarean sections rates. A multi-level logistic regression was used accounting for homogeneity within country, and homogeneity within twin pairs.

Results

Early neonatal mortality among twins was significantly higher when compared to singleton neonates (adjusted odds ratio (aOR) 7.6; 95% confidence interval (CI) = 7.0-8.3) in these 60 countries. Early neonatal mortality was also higher among twins than singletons when adjusting for birth weight in a subgroup analysis of those countries with data on birth weight (n = 20; less than 20% of missing values) (aOR = 2.8; 95% CI = 2.2-3.5). For countries with high rates (>15%) of caesarean sections (CS), twins delivered vaginally in health facility had a statistically significant (aOR = 4.8; 95% CI = 2.4-9.4) increased risk of early neonatal mortality compared to twins delivered through caesarean sections. Home twin births without SBA was associated with increased mortality compared with delivering at home with SBA (aOR = 1.3; 95% CI = 1.0-1.8) and with vaginal birth in health facility (aOR = 1.7; 95% CI = 1.4-2.0).

Conclusions

Institutional deliveries and increased access of caesarian sections may be considered for twin pregnancies in low- and middle- income countries to decrease early adverse neonatal outcomes.

Using health-facility data to assess subnational coverage of maternal and child health indicators, Kenya

Objective

To develop a systematic approach to obtain the best possible national and subnational statistics for maternal and child health coverage indicators from routine health-facility data.

Methods

Our approach aimed to obtain improved numerators and denominators for calculating coverage at the subnational level from health-facility data. This involved assessing data quality and determining adjustment factors for incomplete reporting by facilities, then estimating local target populations based on interventions with near-universal coverage (first antenatal visit and first dose of pentavalent vaccine). We applied the method to Kenya at the county level, where routine electronic reporting by facilities is in place via the district health information software system.

Findings

Reporting completeness for facility data were well above 80% in all 47 counties and the consistency of data over time was good. Coverage of the first dose of pentavalent vaccine, adjusted for facility reporting completeness, was used to obtain estimates of the county target populations for maternal and child health indicators. The country and national statistics for the four-year period 2012/13 to 2015/16 showed good consistency with results of the 2014 Kenya demographic and health survey. Our results indicated a stagnation of immunization coverage in almost all counties, a rapid increase of facility-based deliveries and caesarean sections and limited progress in antenatal care coverage.

Conclusion

While surveys will continue to be necessary to provide population-based data, web-based information systems for health facility reporting provide an opportunity for more frequent, local monitoring of progress, in maternal and child health.

SEX COMPOSITION OF TWINS AND ASSOCIATIONS WITH MORBIDITY, MORTALITY AND MATERNAL TREATMENT-SEEKING OUTCOMES IN RESOURCE-POOR SETTINGS

Societal gender inequality and a preference for male children has been shown to be detrimental to girls' health. This is despite females' innate biological advantage early in life. The negative effects of gender inequity on female health are most pronounced in resource-poor countries, where cultural norms supporting a preference for male children are strongest. However, most of what is known about gender inequality and child health comes from studies of singleton births. There is little evidence for how, or if, the disadvantages associated with gender bias and son preference extend to multiple births, a population inherently at risk for a number of health challenges. This analysis examines whether gender bias in health outcomes exists for twins. Data on live twin births from 38 Demographic and Health Surveys were compiled (n=11,528 individuals) and twins were categorized as girl/girl, girl/boy, boy/girl or girl/girl. Gender inequality was measured via the Gender Inequality Index. Multilevel logistic regression models examined associations between twin sex composition, gender inequality and eight outcomes of infant and child morbidity, mortality and mother's treatment-seeking behaviours. Twin pairs containing girls had significantly lower odds of first-year mortality. Higher country-level gender inequality was associated with higher odds of reporting diarrhoea and fever/cough, as well as an increased odds of post-neonatal mortality. Results suggest that the biological advantage for females may be stronger than son preference and gender inequality in the first year of life. Understanding these relationships has the potential to inform efforts to curb the influence of gender preference on the health of female children in resource-poor settings.

Mortality among twins and singletons in sub-Saharan Africa between 1995 and 2014: a pooled analysis of data from 90 Demographic and Health Surveys in 30 countries

BACKGROUND

Sub-Saharan Africa has the world's highest under-5 and neonatal mortality rates as well as the highest naturally occurring twin rates. Twin pregnancies carry high risk for children and mothers. Under-5 mortality has declined in sub-Saharan Africa over the last decades. It is unknown whether twins have shared in this reduction.

METHODS

We pooled data from 90 Demographic and Health Surveys for 30 sub-Saharan Africa countries on births reported between 1995 and 2014. We used information on 1 685 110 singleton and 56 597 twin livebirths to compute trends in mortality rates for singletons and twins. We examined whether the twin-singleton rate ratio can be attributed to biological, socioeconomic, care-related factors, or birth size, and estimated the mortality burden among sub-Saharan African twins.

FINDINGS

Under-5 mortality among twins has declined from 327·7 (95% CI 312·0-343·5) per 1000 livebirths in 1995-2001 to 213·0 (196·7-229·2) in 2009-14. This decline of 35·0% was much less steep than the 50·6% reduction among singletons (from 128·6 [95% CI 126·4-130·8] per 1000 livebirths in 1995-2001 to 63·5 [61·6-65·3] in 2009-14). Twins account for an increasing share of under-5 deaths in sub-Saharan Africa: currently 10·7% of under-5 mortality and 15·1% of neonatal mortality. We estimated that about 315 000 twins (uncertainty interval 289 000-343 000) die in sub-Saharan African each year. Excess twin mortality cannot be explained by common risk factors for under-5 mortality, including birthweight. The difference with singletons was especially stark for neonatal mortality (rate ratio 5·0, 95% CI 4·5-5·6). 51·7% of women pregnant with twins reported receiving medical assistance at birth.

INTERPRETATION

The fate of twins in sub-Saharan Africa is lagging behind that of singletons. An alarming one-fifth of twins in the region dies before age 5 years, three times the mortality rate among singletons. Twins account for a substantial and growing share of under-5 and neonatal mortality, but they are largely neglected in the literature. Coordinated action is required to improve the situation of this extremely vulnerable group.

FUNDING

None.

Patterns of admission and factors associated with neonatal mortality among neonates admitted to the neonatal intensive care unit of University of Gondar Hospital, Northwest Ethiopia

Introduction

The neonatal period is a highly vulnerable time for an infant completing many of the physiologic adjustments required for life outside the uterus. As a result, there are high rates of morbidity and mortality. The three major causes of mortality in developing countries include prematurity, infection, and perinatal asphyxia. The aim of this study was to identify the patterns of neonatal admission and factors associated with mortality among neonates admitted at the Neonatal Intensive Care Unit (NICU) of University of Gondar Hospital.

Materials and methods

A retrospective cross-sectional study was conducted among all admitted neonates in the NICU of University of Gondar referral hospital from December 1, 2015 to August 31, 2016. Information was extracted retrospectively during admission from patient records and death certificates, using a pretested questionnaire. The data were entered and analyzed using SPSS version 20, and p-values <0.05 were considered statistically significant.

Results

A total of 769 neonates was included in the study. There were 448 (58.3%) male neonates, and 398 (51.8%) neonates were rural residents. More than two-thirds of the 587 deliveries (76.3%) were performed in tertiary hospitals. Neonatal morbidity included hypothermia 546 (71%), sepsis 522 (67.9%), prematurity 250 (34.9%), polycythemia 242 (31.5%), hypoglycemia 142 (18.5), meconium aspiration syndrome 113 (14.7%), and perinatal asphyxia 96 (12.5%). The overall mortality was 110 (14.3%; 95% confidence interval [CI]: 11.9-16.9) of which 69 (62.7%) deaths occurred in the first 24 hours of age. In the multivariate analysis, mortality was associated with perinatal asphyxia (adjusted odds ratio [AOR]: 5.97; 95% CI: 3.06-11.64), instrumental delivery (AOR: 2.99; 95% CI: 1.08-8.31), and early onset neonatal sepsis (AOR: 2.66; 95% CI: 1.62-6.11).

Conclusion

Hypothermia, sepsis, and prematurity were the main reasons for NICU admission. Neonates often died within the first 24 hours of age. Implementing a better referral link and timely intervention could decrease neonatal mortality and morbidities in Gondar, Ethiopia.

Bed rest with and without hospitalisation in multiple pregnancy for improving perinatal outcomes

BACKGROUND

Strict or partial bed rest in hospital or at home is commonly recommended for women with multiple pregnancy to improve pregnancy outcomes. In order to advise women to rest in bed for any length of time, a policy for clinical practice needs to be supported by reliable evidence and weighed against possible adverse effects resulting from prolonged activity restriction.

OBJECTIVES

The objective of this review is to assess the effectiveness of bed rest in hospital or at home to improve perinatal outcomes in women with a multiple pregnancy.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 May 2016), ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) (30 May 2016) and reference lists of retrieved studies.

SELECTION CRITERIA

We selected all individual and cluster-randomised controlled trials evaluating the effect of strict or partial bed rest at home or in hospital compared with no activity restriction during multiple pregnancy.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion, extracted data and methodological quality. We evaluated the quality of the evidence using the GRADE approach and summarised it in 'Summary of findings' tables.

MAIN RESULTS

We included six trials, involving a total of 636 women with a twin or triplet pregnancy (total of 1298 babies). We assessed all of the included trials as having a low risk of bias for random sequence generation. Apart from one trial with an unclear risk of bias, we judged all remaining trials to be of low risk of bias for allocation concealment.Five trials (495 women and 1016 babies) compared strict bed rest in hospital with no activity restriction at home. There was no difference in the risk of very preterm birth (risk ratio (RR) 1.02, 95% confidence interval (CI) 0.66 to 1.58, five trials, 495 women, assuming complete correlation between twins/triplets, low-quality evidence), perinatal mortality (RR 0.65, 95% CI 0.35 to 1.21, five trials, 1016 neonates, assuming independence between twins/triplets, low-quality evidence) and low birthweight (RR 0.95, 95% CI 0.75 to 1.21, three trials, 502 neonates, assuming independence between twins/triplets, low-quality evidence). We observed no differences for the risk of small-for-gestational age (SGA) (RR 0.75, 95% CI 0.56 to 1.01, two trials, 293 women, assuming independence between twins/triplets, low-quality evidence) and prelabour preterm rupture of the membrane (PPROM) (RR 1.30, 95% CI 0.71 to 2.38, three trials, 276 women, low-quality evidence). However, strict bed rest in hospital was associated with increased spontaneous onset of labour (RR 1.05, 95% CI 1.02 to 1.09, P = 0.004, four trials, 488 women) and a higher mean birthweight (mean difference (MD) 136.99 g, 95% CI 39.92 to 234.06, P = 0.006, three trials, 314 women) compared with no activity restriction at home.Only one trial (141 women and 282 babies) compared partial bed rest in hospital with no activity restriction at home. There was no evidence of a difference in the incidence of very preterm birth (RR 2.30, 95% CI 0.84 to 6.27, 141 women, assuming complete correlation between twins, low-quality evidence) and perinatal mortality (RR 4.17, 95% CI 0.90 to 19.31, 282 neonates, assuming complete independence twins, low-quality evidence) between the intervention and control group. Low birthweight was not reported in this trial. We found no differences in the risk of PPROM and SGA between women receiving partial bed rest and the control group (low-quality evidence). Women on partial bed rest in hospital were less likely to develop gestational hypertension compared with women without activity restriction at home (RR 0.30, 95% CI 0.16 to 0.59, P = 0.0004, 141 women).Strict or partial bed rest in hospital was found to have no impact on other secondary outcomes. None of the trials reported on costs of the intervention or adverse effects such as the development of venous thromboembolism or psychosocial effects.

AUTHORS' CONCLUSIONS

The evidence to date is insufficient to inform a policy of routine bed rest in hospital or at home for women with a multiple pregnancy. There is a need for large-scale, multicenter randomised controlled trials to evaluate the benefits, adverse effects and costs of bed rest before definitive conclusions can be drawn.