Frequency of Twin Births in Developed Countries

Brazilian Twin Studies: A Scoping Review

The current study was motivated by an interest in deepening understanding of Brazilian twin research, which is underrepresented internationally, in an effort to rectify this situation. Our aim was threefold: (1) to carry out a comprehensive investigation of Brazilian research on twins according to the area of knowledge; (2) to evaluate the representation of research in the field of psychology in comparison with other areas; (3) to evaluate characteristics of the research that may have contributed to its exclusion from the comprehensive meta-analysis of 50 years of twin research. A scoping review was performed according to PRISMA guidelines. Titles and abstracts were searched up to 2022 in six databases: CAPES, BDLTD, PePSIC, PubMed, Google Scholar, and SciELO, using selected keywords both in Portuguese and in English (e.g., 'twins' and 'Brazil'; 'twinning' and 'Brazil'; 'gemelaridade' [twinning], and 'gêmeos' [twins]). Three hundred and forty publications were included in the review. Approximately half (53.8‰) used the classic twin design to investigate the heritability of several traits, and the other half (46.2%) used other research designs. The scoping review showed that the number of publications doubled approximately every 10 years. Most publications were from the health area, with medicine accounting for approximately half of the studies, followed by psychology, odontology, and biology. We found that the interest in studying twins among Brazilian scientists is increasing over the years and there are reasons to be enthusiastic about the potential impact of this trend in the global scenario.

Genome-wide association study meta-analysis of dizygotic twinning illuminates genetic regulation of female fecundity

STUDY QUESTION

Which genetic factors regulate female propensity for giving birth to spontaneous dizygotic (DZ) twins?

SUMMARY ANSWER

We identified four new loci, GNRH1, FSHR, ZFPM1, and IPO8, in addition to previously identified loci, FSHB and SMAD3.

WHAT IS KNOWN ALREADY

The propensity to give birth to DZ twins runs in families. Earlier, we reported that FSHB and SMAD3 as associated with DZ twinning and female fertility measures.

STUDY DESIGN, SIZE, DURATION

We conducted a genome-wide association meta-analysis (GWAMA) of mothers of spontaneous dizygotic (DZ) twins (8265 cases, 264 567 controls) and of independent DZ twin offspring (26 252 cases, 417 433 controls).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Over 700 000 mothers of DZ twins, twin individuals and singletons from large cohorts in Australia/New Zealand, Europe, and the USA were carefully screened to exclude twins born after use of ARTs. Genetic association analyses by cohort were followed by meta-analysis, phenome wide association studies (PheWAS), in silico and in vivo annotations, and Zebrafish functional validation.

MAIN RESULTS AND THE ROLE OF CHANCE

This study enlarges the sample size considerably from previous efforts, finding four genome-wide significant loci, including two novel signals and a further two novel genes that are implicated by gene level enrichment analyses. The novel loci, GNRH1 and FSHR, have well-established roles in female reproduction whereas ZFPM1 and IPO8 have not previously been implicated in female fertility. We found significant genetic correlations with multiple aspects of female reproduction and body size as well as evidence for significant selection against DZ twinning during human evolution. The 26 top single nucleotide polymorphisms (SNPs) from our GWAMA in European-origin participants weakly predicted the crude twinning rates in 47 non-European populations (r = 0.23 between risk score and population prevalence, s.e. 0.11, 1-tail P = 0.058) indicating that genome-wide association studies (GWAS) are needed in African and Asian populations to explore the causes of their respectively high and low DZ twinning rates. In vivo functional tests in zebrafish for IPO8 validated its essential role in female, but not male, fertility. In most regions, risk SNPs linked to known expression quantitative trait loci (eQTLs). Top SNPs were associated with in vivo reproductive hormone levels with the top pathways including hormone ligand binding receptors and the ovulation cycle.

LARGE SCALE DATA

The full DZT GWAS summary statistics will made available after publication through the GWAS catalog (https://www.ebi.ac.uk/gwas/).

LIMITATIONS, REASONS FOR CAUTION

Our study only included European ancestry cohorts. Inclusion of data from Africa (with the highest twining rate) and Asia (with the lowest rate) would illuminate further the biology of twinning and female fertility.

WIDER IMPLICATIONS OF THE FINDINGS

About one in 40 babies born in the world is a twin and there is much speculation on why twinning runs in families. We hope our results will inform investigations of ovarian response in new and existing ARTs and the causes of female infertility.

STUDY FUNDING/COMPETING INTEREST(S)

Support for the Netherlands Twin Register came from the Netherlands Organization for Scientific Research (NWO) and The Netherlands Organization for Health Research and Development (ZonMW) grants, 904-61-193, 480-04-004, 400-05-717, Addiction-31160008, 911-09-032, Biobanking and Biomolecular Resources Research Infrastructure (BBMRI.NL, 184.021.007), Royal Netherlands Academy of Science Professor Award (PAH/6635) to DIB, European Research Council (ERC-230374), Rutgers University Cell and DNA Repository (NIMH U24 MH068457-06), the Avera Institute, Sioux Falls, South Dakota (USA) and the National Institutes of Health (NIH R01 HD042157-01A1) and the Genetic Association Information Network (GAIN) of the Foundation for the National Institutes of Health and Grand Opportunity grants 1RC2 MH089951. The QIMR Berghofer Medical Research Institute (QIMR) study was supported by grants from the National Health and Medical Research Council (NHMRC) of Australia (241944, 339462, 389927, 389875, 389891, 389892, 389938, 443036, 442915, 442981, 496610, 496739, 552485, 552498, 1050208, 1075175). L.Y. is funded by Australian Research Council (Grant number DE200100425). The Minnesota Center for Twin and Family Research (MCTFR) was supported in part by USPHS Grants from the National Institute on Alcohol Abuse and Alcoholism (AA09367 and AA11886) and the National Institute on Drug Abuse (DA05147, DA13240, and DA024417). The Women's Genome Health Study (WGHS) was funded by the National Heart, Lung, and Blood Institute (HL043851 and HL080467) and the National Cancer Institute (CA047988 and UM1CA182913), with support for genotyping provided by Amgen. Data collection in the Finnish Twin Registry has been supported by the Wellcome Trust Sanger Institute, the Broad Institute, ENGAGE-European Network for Genetic and Genomic Epidemiology, FP7-HEALTH-F4-2007, grant agreement number 201413, National Institute of Alcohol Abuse and Alcoholism (grants AA-12502, AA-00145, AA-09203, AA15416, and K02AA018755) and the Academy of Finland (grants 100499, 205585, 118555, 141054, 264146, 308248, 312073 and 336823 to J. Kaprio). TwinsUK is funded by the Wellcome Trust, Medical Research Council, Versus Arthritis, European Union Horizon 2020, Chronic Disease Research Foundation (CDRF), Zoe Ltd and the National Institute for Health Research (NIHR) Clinical Research Network (CRN) and Biomedical Research Centre based at Guy's and St Thomas' NHS Foundation Trust in partnership with King's College London. For NESDA, funding was obtained from the Netherlands Organization for Scientific Research (Geestkracht program grant 10000-1002), the Center for Medical Systems Biology (CSMB, NVVO Genomics), Biobanking and Biomolecular Resources Research Infrastructure (BBMRI-NL), VU University's Institutes for Health and Care Research (EMGO+) and Neuroscience Campus Amsterdam, University Medical Center Groningen, Leiden University Medical Center, National Institutes of Health (NIH, ROI D0042157-01A, MH081802, Grand Opportunity grants 1 RC2 Ml-1089951 and IRC2 MH089995). Part of the genotyping and analyses were funded by the Genetic Association Information Network (GAIN) of the Foundation for the National Institutes of Health. Computing was supported by BiG Grid, the Dutch e-Science Grid, which is financially supported by NWO. Work in the Del Bene lab was supported by the Programme Investissements d'Avenir IHU FOReSIGHT (ANR-18-IAHU-01). C.R. was supported by an EU Horizon 2020 Marie Skłodowska-Curie Action fellowship (H2020-MSCA-IF-2014 #661527). H.S. and K.S. are employees of deCODE Genetics/Amgen. The other authors declare no competing financial interests.

TRIAL REGISTRATION NUMBER

N/A.

Gender gaps in Mathematics and Language: The bias of competitive achievement tests

This research paper examines the extent to which high-stakes competitive tests affect gender gaps in standardized tests of Mathematics and Language. To this end, we estimate models that predict students' results in two national standardized tests: a test that does not affect students' educational trajectory, and a second test that determines access to the most selective universities in Chile. We used data from different gender twins who took these tests. This strategy allows us to control, through household fixed effects, the observed and unobserved household characteristics. Our results show that competitive tests negatively affect women. In Mathematics, according to both tests, there is a gender gap in favor of men, which increases in the university entrance exam, especially for high-performance students. As the literature review shows, women are negatively stereotyped in Mathematics, so this stereotype threat could penalize high-achieving women, that is, those that go against the stereotype. In Language tests, women outperform men in the standardized test taken in high school, but the situation is reversed in the university entrance exam. From our analysis of Chilean national data, we find no evidence that the gender effect observed in the competitive test depends on the students' achievement level. Following the literature, this gender gap may be linked to women's risk aversion, lower self-confidence, lower preference for competition, as well as the effect of answering a test under time pressure.

Temporal trends and adverse perinatal outcomes of twin pregnancies at differing gestational ages: an observational study from China between 2012–2020

Background

With the development of assisted reproductive technology, the twinning rate in China has been increasing. However, little is known about twinning from 2014 onwards. In addition, previous studies analysing optimal gestational times have rarely considered maternal health conditions. Therefore, whether maternal health conditions affect the optimal gestational time remains unclear.

Methods

Data of women delivered between January 2012 and December 2020 were collected through China’s National Maternal Near Miss Surveillance System. Interrupted time series analysis was used to determine the rates of twinning, stillbirth, smaller than gestational age (SGA), and low Apgar scores (< 4) among twins in China. To estimate the risk of each adverse perinatal outcome for separate gestational weeks, a multivariate generalised linear model was used. Infants born at 37 weeks of gestational age or foetuses staying in utero were used as reference separately. The analyses were adjusted for the sampling distribution of the population and the cluster effect at the hospital and individual levels were considered.

Results

There were 442,268 infants enrolled in this study, and the adjusted rates for twinning, stillbirth, SGA, and low Apgar scores were 3.10%, 1.75%, 7.70%, and 0.79%, respectively. From 2012 to 2020, the twinning rate showed an increasing trend. Adverse perinatal outcomes, including stillbirth, SGA, and low Apgar scores showed a decreasing trend. A gestational age between 34 and 36 weeks decreased most for rate of stillbirth (average changing rate -9.72%, 95% confidence interval [CI] -11.41% to -8.00%); and a gestational age of between 37 and 38 weeks decreased most for rates of SGA (average changing rate -4.64%, 95% CI -5.42% to -3.85%) and low Apgar scores (average changing rate -17.61%, 95% CI -21.73% to -13.26%). No significant difference in changes in twinning rate or changes of each perinatal outcome was observed during periods of different fertility policies. Infants born at 37 weeks of gestation had a decreased risk of stillbirth, SGA, and low Apgar scores. Maternal antepartum or medical complications increased the risk of SGA and low Apgar scores in different gestational weeks.

Conclusion

China’s twinning rate showed an increasing trend, while adverse perinatal outcomes decreased from 2012 to 2020. Fertility policy changes have had little effect on the twinning rate or the rate of adverse perinatal outcomes such as stillbirth, SGA, or low Apgar scores. The optimal gestational age for twins was 37 weeks. Women pregnant with twins and with antepartum or medical complications should be cautious due to an increased risk of SGA and low Apgar scores.

The Heritability of Twinning in Seven Large Historic Pedigrees

It is widely recognized that dizygotic twinning (DZT) runs in families, but estimates of heritability from twin and family data are remarkably scarce and vary considerably. Here, we traced seven large, sometimes historical, multigeneration pedigrees from West Africans, fin de siècle French Jews, Canadians (two pedigrees), and the French royal family, in which twin births were recorded. We estimated heritability of twinning (of all types) as zygosity information was not available, diluting the true DZT heritability by a third or so. The estimates in the range 8-20% are remarkably consistent across time (8-19 generations) and ethnicities and also consistent with twin and family estimates.

Qualitative Investigation into Pre- and Post-Natal Experience of Parents of Triplets

Although parents of triplets experience substantial mental distress, research about this increasing population has primarily focused on physical health risks of triplets and mothers, failing to capture the subjective wellbeing of parents. Accordingly, this study aimed to understand first-hand experience of parents of triplets, using thematic analysis of semi-structured interviews participated by eight parents (four couples: Age M = 48.63, SD = 10.61 years). Six themes were identified: (1) Negative and (2) Positive experiences of raising triplets prenatally and postnatally, (3) Social, psychological, and material support, (4) Experiences and challenges specific to mothers and (5) fathers, and (6) Advice for future parents. These themes suggest that being reassured and accepting support from others are particularly essential in reducing stress and anxiety. Self-compassion interventions were recommended to support the wellbeing of parents of triplets. Our findings will help parents of triplets, their social circles, and healthcare workers to develop effective approaches to reduce the mental health difficulties that this under-researched population experiences.

Prevalence and outcomes of twin pregnancies in Botswana: a national birth outcomes surveillance study

OBJECTIVES

This study aims to evaluate the prevalence and outcome of twin pregnancies in Botswana.

SETTING

The Tsepamo Study conducted birth outcomes surveillance at 8 government-run hospitals (~45% of all births in Botswana) from August 2014 to June 2018 and expanded to 18 hospitals (~70% of all births in Botswana) from July 2018 to March 2019.

PARTICIPANTS

Data were collected for all live-born and stillborn in-hospital deliveries with a gestational age (GA) greater than 24 weeks. This analysis included 117 593 singleton and 3718 twin infants (1859 sets (1.6%)) born to 119 477 women between August 2014 and March 2019 and excluded 73 higher order multiples (23 sets of triplets and 1 set of quadruplets).

OUTCOMES MEASURED

Our primary outcomes were preterm delivery (<37 weeks GA), very preterm delivery (<32 weeks GA) and stillbirth (APGAR (Appearance, Pulse, Grimace, Activity, Respiration) score of 0, 0, 0).

RESULTS

Women with twin pregnancies had a similar median number of antenatal care visits (9 vs 10), but were more likely to deliver in a tertiary centre (54.8% vs 45.1%, p<0.001) and more likely to have a cesarean-section (54.6% vs 22.0%, p<0.001) than women with singletons. Compared with singletons, twin pregnancies had a higher risk of preterm delivery (<37 weeks GA) (47.6% vs 16.7%, adjusted risk ratio (aRR) 2.8, 95% CI 2.7 to 2.9) and very preterm delivery (<32 weeks) (11.8% vs 4.0%, aRR 3.0 95% CI 2.6 to 3.4). Among all twin pregnancies, 128 (6.9%) had at least one stillborn infant compared with 2845 (2.4%) stillbirths among singletons (aRR 2.8, 95% CI 2.3 to 3.3).

CONCLUSION

Adverse birth outcomes are common among twins in Botswana, and are often severe. Interventions that allow for earlier identification of twin gestation and improved antenatal management of twin pregnancies may improve infant and child survival.

Influence of the placental cord insertion site on the placental mass and the birth weight in dichorionic diamniotic twins

The aim of the study was to determine the effect of the displacement of the umbilical cord insertion site from the centre of the placenta on the placental mass and the birth weight of dichorionic diamniotic twins and to consider the importance of the direction of the displacement, as well as to assess the influence of the umbilical cord displacement on the placental mass and the birth weight of dichorionic diamniotic twins taking into account the direction of displacement. Material and methods. The study was performed on 135 dichorionic diamniotic pairs: 68 opposite-sex, 35 same-sex males, and 32 same-sex females. The impact of an absolute cord displacement from the centroid of the placental disc and the direction of its shifting were compared with the birth weight and the placental mass. Results. In the investigated group, a central insertion was revealed in 6 (2.2 %), eccentric – in 224 (83.0 %), marginal – in 31 (11.5 %), and velamentous – in 9 (3.3 %) cases. The first two types of cord insertion are considered to be normal, the third and the fourth are seen as abnormal. The placental mass was in a strong positive correlation with the birth weight (r=0.71, p<0.0001). The placentas with an eccentric cord insertion had a smaller surface area. A negative correlation was established between the displacement of the cord insertion site and the placental mass (r=-0.4284, p<0.0001) as well as the birth weight (r=-0.6115, p<0.0001). The shift along the long axis was of greater importance than in relation to the shorter one. The placental mass and the birth weight were higher in the new-borns with a normal cord insertion site. In the abnormal cord insertion group, 32.5 % of the infants were under the 10th birth weight percentile, in the normal cord insertion group – only 8.3 %. Conclusions. The birth weight of dichorionic diamniotic twins and their placental mass are negatively correlated with the distance of the umbilical cord insertion site from the placental centre. The insertion site displacement along the long axis has a stronger negative effect on the birth weight and the placental mass in comparison with the shifting along the short axis. The placentas with an eccentric cord insertion have a smaller surface area.

Twin Peaks: more twinning in humans than ever before

STUDY QUESTION

How many twins are born in human populations and how has this changed over recent decades?

SUMMARY ANSWER

Since the 1980s, the global twinning rate has increased by a third, from 9.1 to 12.0 twin deliveries per 1000 deliveries, to about 1.6 million twin pairs each year.

WHAT IS KNOWN ALREADY

It was already known that in the 1980s natural twinning rates were low in (East) Asia and South America, at an intermediate level in Europe and North America, and high in many African countries. It was also known that in recent decades, twinning rates have been increasing in the wealthier parts of our world as a result of the rise in medically assisted reproduction (MAR) and delayed childbearing.

STUDY DESIGN, SIZE, DURATION

We have brought together all information on national twinning rates available from statistical offices, demographic research institutes, individual survey data and the medical literature for the 1980-1985 and the 2010-2015 periods.

PARTICIPANTS/MATERIALS, SETTING, METHODS

For 165 countries, covering over 99% of the global population, we were able to collect or estimate twinning rates for the 2010-2015 period. For 112 countries, we were also able to obtain twinning rates for 1980-1985.

MAIN RESULTS AND THE ROLE OF CHANCE

Substantial increases in twinning rates were observed in many countries in Europe, North America and Asia. For 74 out of 112 countries the increase was more than 10%. Africa is still the continent with highest twinning rates, but Europe, North America and Oceania are catching up rapidly. Asia and Africa are currently home to 80% of all twin deliveries in the world.

LIMITATIONS, REASONS FOR CAUTION

For some countries, data were derived from reports and papers based on hospital registrations which are less representative for the country as a whole than data based on public administrations and national surveys.

WIDER IMPLICATIONS OF THE FINDINGS

The absolute and relative number of twins for the world as a whole is peaking at an unprecedented level. An important reason for this is the tremendous increase in medically assisted reproduction in recent decades. This is highly relevant, as twin deliveries are associated with higher infant and child mortality rates and increased complications for mother and child during pregnancy and during and after delivery.

STUDY FUNDING/COMPETING INTEREST(S)

The contribution of CM was partially supported by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant No 681546, FAMSIZEMATTERS), Nuffield College, and the Leverhulme Trust. The contribution of GP was partially supported by the French Agence Nationale de la Recherche (grant No ANR-18-CE36-0007-07). The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Twins Support the Absence of Parity-Dependent Fertility Control in Pretransition Populations

A conclusion of the European Fertility Project in 1986 was that pretransition populations mostly displayed natural fertility, where parity-dependent birth control was absent. This conclusion has recently been challenged for England by new empirical results and has also been widely rejected by theorists of long-run economic growth, where pre-industrial fertility control is integral to most models. In this study, we use the accident of twin births to show that for three Western European-derived pre-industrial populations-namely, England (1730-1879), France (1670-1788), and Québec (1621-1835)-we find no evidence for parity-dependent control of marital fertility. If a twin was born in any of these populations, family size increased by 1 compared with families with a singleton birth at the same parity and mother age, with no reduction of subsequent fertility. Numbers of children surviving to age 14 also increased. Twin births also show no differential effect on fertility when they occurred at high parities; this finding is in contrast to populations where fertility is known to have been controlled by at least some families, such as in England, 1900-1949, where a twin birth increased average births per family by significantly less than 1.

Is there something special about twin families? A comparison of parenting styles in twin and non-twin families

Twin comparisons offer a powerful quasi-experimental design to study the impact of the family of origin on children's life chances. Yet, there are concerns about the generalizability of results obtained from twin studies because twin families are structurally different and twins have a genetic resemblance. We examine these concerns by comparing mothers' reports on their parenting styles for twin and non-twin children between twin and non-twin families, as well as within twin families. We use two German studies for our comparisons: TwinLife and pairfam. Our results demonstrate that twins receive more differential treatment and more emotional warmth than non-twins; however, these differences are largely accounted for by age differences between children. Overall, our results indicate that results on parenting obtained from twin studies can be generalized to non-twin families.

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.

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 genetic and environmental etiology of child maltreatment in a parent-based extended family design

Child maltreatment has been associated with various cumulative risk factors. However, little is known about the extent to which genetic and environmental factors contribute to individual differences between parents in perpetrating child maltreatment. To estimate the relative contribution of genetic and environmental factors to perpetrating maltreatment we used a parent-based extended family design. Child-reported perpetrated maltreatment was available for 556 parents (283 women) from 63 families. To explore reporter effects (i.e., child perspective on maltreatment), child reports were compared to multi-informant reports. Based on polygenic model analyses, most of the variance related to the perpetration of physical abuse and emotional neglect was explained by common environmental factors (physical abuse: c2 = 59%, SE = 12%, p = .006; emotional neglect: c2 = 47%, SE = 8%, p &lt; .001) whereas genetic factors did not significantly contribute to the model. For perpetrated emotional abuse, in contrast, genetic factors did significantly contribute to perpetrated emotional abuse (h2 = 33%, SE = 8%, p &lt; .001), whereas common environment factors did not. Multi-informant reports led to similar estimates of genetic and common environmental effects on all measures except for emotional abuse, where a multi-informant approach yielded higher estimates of the common environmental effects. Overall, estimates of unique environment, including measurement error, were lower using multi-informant reports. In conclusion, our findings suggest that genetic pathways play a significant role in perpetrating emotional abuse, while physical abuse and emotional neglect are transmitted primarily through common environmental factors. These findings imply that interventions may need to target different mechanisms dependings on maltreatment type.

Incidence and short outcome in multiple pregnancies: a single center cross-sectional study in Iran 2016–2017

BACKGROUND The incidence of multiple pregnancies in industrialized countries due to the use of assisted reproductive techniques has increased over the past two decades. Multiple births are more dangerous than single pregnancies for mother and baby. This study evaluated the frequency of multiple pregnancies and its neonatal complications.METHODS In this cross-sectional study, we assessed all multiple neonates hospitalized in Fatemieh Hospital of Hamadan, Iran from September 2016 to September 2017 in terms of gender, gestational age, birth weight, the use of assisted reproductive techniques, delivery method, cause of hospitalization, therapeutic intervention, and hospitalization outcome.RESULTS Of 10,581 deliveries during the study period, 351 (3.3%) was multiple pregnancies and 232 neonates hospitalized. The incidence of twin, triplet, and quadruplet birth were 1.7%, 0.39%, and 0.11% respectively. In this study, 178 twin and 54 triplet and quadruplet birth were compared. The mean gestational age and mean birth weight of triplet and quadruplet were lower than that of twin births (p<0.001). A significant difference was found on the frequency of assisted reproductive techniques (p<0.001). Female sex (p=0.007), lower mean gestational age (p=0.009), lower mean birth weight (p=0.017) and need to mechanical ventilation (p<0.001) were significantly associated with early neonatal death in multiple pregnancies.CONCLUSIONS The incidence of multiple births was high in the Hamadan province, which was often followed by infertility treatment. Moreover, multiple births cause prematurity, low birth weight, respiratory distress syndrome, and increased neonatal mortality rate.

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.

Delayed interval delivery in multiple gestations: the Munich experience

OBJECTIVE

To evaluate delayed interval deliveries in multiple gestations in regard of delayed interval and neonatal survival and to provide a protocol.

METHODS

Data of multiple pregnancies with delayed interval delivery at a tertiary maternity unit between 2002 and 2017 were collected. Contraindications for evaluation of a delay of the delivery of the remaining child were: severe maternal blood loss, poor maternal general condition, preeclampsia, placental abruption, fetal distress, serious congenital malformations of the remaining child, chorioamnionitis, and premature rupture of membranes of the second fetus. A total of 14 cases was included in this retrospective monocentric analysis.

RESULTS

The cohort comprised nine twin and five triplet pregnancies. Mean gestational age at delivery of the first fetus was 21 + 6 and 26 + 0 of the retained fetus, respectively. The earliest delivery of the first fetus was at 15 + 2 weeks. The mean interval of the delay was 29.3 days (2-82 days). Mortality of the first fetuses was 53.3%, while it was 17.6% for the retained fetuses. Maternal outcome was good in general: two cases of major blood loss occurred with the necessity of a blood transfusion.

CONCLUSION

Delayed interval delivery is a reasonable approach in cases of an imminent preterm birth in multiple gestations which can be performed with a good fetal outcome and limited maternal risks. The situation when this procedure may be an option always comes unexpected. Therefore, the team of perinatologists should keep it in mind as one potential therapeutic approach. In addition, a standard protocol for the procedure should be established in the perinatal center.

Performance of non-invasive prenatal testing for trisomies 21 and 18 in twin pregnancies

Background

Cell-free fetal DNA in maternal plasma represents a source of fetal genetic material that can be sampled noninvasively. There are ample studies confirming the accuracy of NIPT in singleton pregnancies, but there is still relatively little studies demonstrate the feasibility and clinical application of a NIPT for fetal aneuploidy screening in twin pregnancies.

Results

In this study, we have finished 432 twin pregnancies screening by NIPT. There were 4 double chorionic dichorionic diamniotic (DCDA) cases of true positive NIPT results, including 1of T18 and 3 of T21, and 1 monochorionic diamniotic (MCDA) cases of true positive NIPT results, including 1of T21. The combined false-positive frequency for trisomies 21, 18 was 0%. Furthermore, there were 2 cases of false positive NIPT results, including 1 of T7 and 1 of sex chromosome aneuploidy. There was no false negative case, which gave a combined sensitivity and specificity of 100 and 99.53% respectively.

Conclusion

Our study demonstrated NIPT performed well in the detection of trisomy 21 in twin pregnancy. It is feasible and clinical applicable of NIPT for fetal aneuploidy screening in twin pregnancies. But, it needs a large number of clinical samples to demonstrate the applicability of other chromosomal abnormalities besides trisomies 21 and 18 in both singleton pregnancies and twin pregnancies.

Beckwith Wiedemann syndrome: A population-based study on prevalence, prenatal diagnosis, associated anomalies and survival in Europe

Beckwith Wiedemann syndrome is a complex developmental disorder characterized by somatic overgrowth, macroglossia, abdominal wall defects, neonatal hypoglycemia, and predisposition to embryonal tumors. We present epidemiological and clinical aspects of patients with Beckwith Wiedemann syndrome diagnosed prenatally or in the early years of life, using data from EUROCAT (European Surveillance of Congenital Anomalies) registries. The study population consisted of 371 cases identified between January 1990 and December 2015 in 34 registries from 16 European countries. There were 15 (4.0%) terminations of pregnancy after prenatal detection of severe anomaly/anomalies, 10 fetal deaths (2.7%), and 346 (93.3%) live-births. Twelve (3.6%) of the 330 live-births with available information on survival died in the first week of life, of those eleven (91.6%) were preterm. First-year survival rate was 90.9%. Prematurity was present in 40.6% of males and 33.9% of females. Macrosomia was found in 49.2% and 43.3% of preterm males and females, respectively. Of term newborns, 41.1% of males and 24% of females were macrosomic. Out of 353 cases with known time of diagnosis, 39.9% were suspected prenatally, 36.3% at birth, 7.6% were diagnosed in the first week of life, and 16.2% in the first year of life. The mean gestational age at prenatal diagnosis by obstetric ultrasound was 19.8 ± 6.2 (11-39) gestational weeks. The mean prenatal diagnosis of cases where parents opted for termination of pregnancy was 15.3 ± 2.4 (11-22) gestational weeks, and the mean gestational age at termination was 19.3 ± 4.1 (13-26) gestational weeks. The prenatal detection rate was 64.1% (141/220) with no significant change over time. There were 12.7% of familial cases. The study confirmed the association of assisted reproductive technologies with Beckwith Wiedemann syndrome, as 7.2% (13/181) of patients were conceived by one of the methods of assisted reproductive technologies, which was three times higher compared to the general population of the countries included in the study. Twin pregnancies of undetermined zygosity were recorded in 5.7% (21/365) cases, and were on average three to four times more common than in European countries that participated in the study. The estimated mean prevalence of classical Beckwith Wiedemann syndrome in Europe was 3.8 per 100,000 births or 1:26,000 births.

Clinical and cytogenomic findings in OAV spectrum

The oculoauriculovertebral spectrum (OAVS) is characterized by anomalies involving the development of the first and second pharyngeal arches during the embryonic period. The phenotype is highly heterogeneous, involving ears, eyes, face, neck, and other systems and organs. There is no agreement in the literature for the minimum phenotypic inclusion criteria, but the primary phenotype involves hemifacial microsomia with facial asymmetry and microtia. Most cases are sporadic and the etiology of this syndrome is not well known. Environmental factors, family cases that demonstrate Mendelian inheritance, such as preauricular appendages, microtia, mandibular hypoplasia, and facial asymmetry; chromosomal abnormalities and some candidate genes suggest a multifactorial inheritance model. We evaluated clinical, cytogenomic and molecularly 72 patients with OAVS, and compared our findings with patients from the literature. We found 15 CNVs (copy number variations) considered pathogenic or possibly pathogenic in 13 out of 72 patients. Our results did not indicated a single candidate genomic region, but recurrent chromosomal imbalances were observed in chromosome 4 and 22, in regions containing genes relevant to the OAVS phenotype or related to known OMIM diseases suggesting different pathogenic mechanisms involved in this genetically and phenotypic heterogeneous spectrum.

Complications in multiple gestation pregnancy: A cross-sectional study of ten maternal-fetal medicine centers in China

Complications in women with multiple gestation pregnancy have not been studied in China. We aimed to establish a database of women with multiple gestation pregnancy and investigate the complications related to multiple pregnancy. We conducted a cross-sectional study that included 3246 women with multiple gestation pregnancy and who had multiple live-birth deliveries; the women were registered at ten maternal-fetal medicine centers in China in 2013. All participants completed a detailed questionnaire that included basic demographic information, history of gestation and abnormal fetal development, risk factors during pregnancy, and pregnancy outcomes. Overall, 1553 (47.8%) women experienced pregnancy complications; these women were more likely to have lower height and less education than women who did not experience complications. However, women who experienced complications had a higher twin birth rate and were more likely to have received regular antenatal care and assisted reproductive technology than women without complications (P < 0.05). Notably, preterm birth was a primary complication in multiple pregnancy (n = 960). In conclusion, pregnancy complications, especially preterm birth, were relatively common in women with multiple gestation pregnancy. The findings from this cross-sectional study in China may be used as a foundation for investigating risk factors for complications in women with multiple gestation pregnancy in the future.

Maxillofacial features and systemic malformations in expanded spectrum Hemifacial Microsomia

Hemifacial microsomia (HFM) is a rare, multisystemic congenital disease with estimated frequency of 1/26370 births in Europe. Most cases are sporadic and caused by unilateral abnormal morphogenesis of the first and second pharyngeal arches. The aim of this study is to define the types and frequency of maxillofacial and systemic malformations in HFM patients. This is a case series study of patients with HFM evaluated at a single institution. Data were acquired through history, physical examination, photographs, diagnostic radiology, and laboratory and analyzed by the FileMakerPro database on 95 patients (54F; 41M) of which 89 met the inclusion criteria. Mandibular hypoplasia was observed in 86 patients with right-side preponderance (50). One patient had bilateral mandibular hypoplasia. Seventy-four had external ear anomalies (anotia or microtia). Eleven had bilateral malformed ears. Hearing impairment, associated with stenosis or atresia of the external ear canal, was found in 69 patients (eight with bilateral canal defects). Ocular anomalies were seen in 41 (23 with dermoid cysts) and 39 had orbital malformations. Facial nerve paralysis was observed in 38 patients. Cleft lip/palate (10), preauricular tags (55), and macrostomia (41) were also described. A total of 73/86 had systemic malformations, mainly vertebral (40), genitourinary (25), and cardiovascular (28). Sixteen had cerebral anomalies (four with intellectual disability). All patients suspected of HFM should undergo a complete systematic clinical and imaging investigation to define the full scope of anomalies. Since the disease is rare and complex, affected patients should be monitored by specialized multidisciplinary team centers.

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.

Twinning and Multiple Birth Rates According to Maternal Age in the City of São Paulo, Brazil: 2003–2014

The present study investigates the twinning rates in the city of São Paulo, Brazil, during the years 2003–2014. The data were drawn from the Brazilian Health Department database of Sistema de Informações de Nascidos Vivos de São Paulo—SINASC (Live Births Information System of São Paulo). In general, more information is available on the incidence of twinning in developed countries than in developing ones. A total of 24,589 twin deliveries and 736 multiple deliveries were registered in 140 hospitals of São Paulo out of a total of 2,056,016 deliveries during the studied time period. The overall average rates of singleton, twin, and multiple births per 1,000 maternities (‰) were 987.43, 11.96 (dizygotic (DZ) rate was 7.15 and monozygotic (MZ) 4.42), and 0.36, respectively. We further regressed maternal age and historical time period on percentage of singleton, twin, and multiple birth rates. Our results indicated that maternal age strongly positively predicted twin and multiple birth rates, and negatively predicted singleton birth rates. The historical time period also positively, although weakly, predicted twin birth rates, and had no effect on singleton or multiple birth rates. Further, after applying Weinberg's differential method, we computed regressions separately for the estimated frequencies of DZ and MZ twin rates. DZ twinning was strongly positively predicted by maternal age and, to a smaller degree, by time period, while MZ twinning increased marginally only with higher maternal age. Factors such as increasing body mass index or air pollution can lead to the slight historical increase in DZ twinning rates. Importantly, consistent with previous cross-cultural and historical research, our results support the existence of an age-dependent physiological mechanism that leads to a strong increase in twinning and multiple births, but not singleton births, among mothers of higher age categories. From the ultimate perspective, twinning and multiple births in later age can lead to higher individual reproductive success near the end of the reproductive career of the mother.

Multiple births in sub-saharan Africa: epidemiology, postnatal survival, and growth pattern

The study endeavored to assess the epidemiology, postnatal survival, and growth pattern of multiple births in Sub-Saharan Africa (SSA). It was based on the data of 25 demographic health surveys conducted in the subcontinent since 2008. The records of 213,889 children born in the preceding 59 months of the surveys were included. The multiple birth rate was computed as the number of multiple confinements per 1,000 births. Factors associated with multiple births were identified using logistic regression and their survival pattern was assessed using the Kaplan-Meier method. The multiple birth rate was 17.1 (95% confidence interval: 17.7-16.6) and showed considerable variation across the 25 countries included in the study. Odds of multiple births were significantly increased with advanced maternal age, parity, and maternal height but not with wealth index, age at first birth, and month of birth. At the end of the fourth year of age, the cumulative survival probability was as low as 0.77 in multiple births as compared to 0.93 in their counterparts. The odds of neonatal, infant and under-five mortality were 5.55, 4.39, and 3.72 times increased in multiple births, respectively. Multiple births tend to be malnourished than singletons and the odds of wasting, stunting, and underweight were 1.31, 1.83, and 1.73 times raised, consecutively. Nevertheless, multiple births regain their weight-for-age (WFA) and height-for-age (HFA) deficits by the end of the fourth year of age. Counseling pregnant mothers with multiple gestation to give birth at a health institution and providing close medical follow-up during and after the neonatal period can improve the survival of multiple births.

Overrepresentation of multiple birth pregnancies in young infants with four metabolic bone disorders: further evidence that fetal bone loading is a critical determinant of fetal and young infant bone strength

The frequency of multiple birth pregnancies, mostly twin pregnancies, was overrepresented in four different groups of young infants with fractures and bone abnormalities. This finding suggests that fetal bone loading through fetal movement is an important determinant of fetal bone formation and its resultant bone strength.

INTRODUCTION

It has been suggested that intrauterine confinement related to the multiple birth pregnancy (MBP) may lead to an increased risk for fragility fractures in young infants as a result of decreased fetal bone loading.

METHODS

To objectively test this idea, the frequency of MBPs was evaluated in five groups of young infants with bone disorders: (1) infants exposed to prolonged in utero exposure to magnesium, (2) infants with dietary copper deficiency, (3) infants with rickets from vitamin D deficiency, (4) infants with temporary brittle bone disease, and (5) infants with multiple unexplained fractures in which child abuse was the most likely diagnosis.

RESULTS

Compared to a control group and controlled for preterm birth, there was a statistically greater frequency of MBPs in each group.

CONCLUSIONS

The results of this study suggest the following: (a) The overrepresentation of MBPs (95 % twins) in these five groups indicates that fetal bone loading is a critical determinant of fetal bone strength; (b) fetal and young infant bone strength is a multifactorial characteristic; and (c) infants from MBPs are at increased risk for fragility fractures during the first 12 months of life, and thus may be mistakenly diagnosed as victims of child abuse.

Unconscious dynamics in twin pregnancy emerging from the Lüscher color test

OBJECTIVE

To investigate unconscious dynamics in women pregnant with twins, using Lüscher's color test to objectively measure subjective color preferences, and compare them with women with singleton pregnancies.

METHODS

The color test was administered to 50 Italian women with twin pregnancies and 100 women with singleton pregnancies.

RESULTS

Both the twin and singleton pregnancy groups said that violet was their favorite color (50 versus 49%) and brown was their least favorite color (52 versus 44%), indicating that they idealized being pregnant, but also found it physically stressful. The twin pregnancy group chose yellow as their second favorite (28 versus 17%) and were most likely to combine it with their first choice of violet (44 versus 19%, p=0.0006), indicating that they were worried about their relationships with their new babies and wanted to give birth soon. In addition, both groups preferred form 6, the sine curve on a dark background, but rejected the associated brown color 6, revealing that the women felt the need to look after themselves.

CONCLUSIONS

Both groups idealized being pregnant, but also found it physically stressful. However, the twin pregnancy group was afraid of building relationships with their babies and wanted to give birth soon.

Prevalence, prenatal diagnosis and clinical features of oculo-auriculo-vertebral spectrum: a registry-based study in Europe

Oculo-auriculo-vertebral spectrum is a complex developmental disorder characterised mainly by anomalies of the ear, hemifacial microsomia, epibulbar dermoids and vertebral anomalies. The aetiology is largely unknown, and the epidemiological data are limited and inconsistent. We present the largest population-based epidemiological study to date, using data provided by the large network of congenital anomalies registries in Europe. The study population included infants diagnosed with oculo-auriculo-vertebral spectrum during the 1990-2009 period from 34 registries active in 16 European countries. Of the 355 infants diagnosed with oculo-auriculo-vertebral spectrum, there were 95.8% (340/355) live born, 0.8% (3/355) fetal deaths, 3.4% (12/355) terminations of pregnancy for fetal anomaly and 1.5% (5/340) neonatal deaths. In 18.9%, there was prenatal detection of anomaly/anomalies associated with oculo-auriculo-vertebral spectrum, 69.7% were diagnosed at birth, 3.9% in the first week of life and 6.1% within 1 year of life. Microtia (88.8%), hemifacial microsomia (49.0%) and ear tags (44.4%) were the most frequent anomalies, followed by atresia/stenosis of external auditory canal (25.1%), diverse vertebral (24.3%) and eye (24.3%) anomalies. There was a high rate (69.5%) of associated anomalies of other organs/systems. The most common were congenital heart defects present in 27.8% of patients. The prevalence of oculo-auriculo-vertebral spectrum, defined as microtia/ear anomalies and at least one major characteristic anomaly, was 3.8 per 100,000 births. Twinning, assisted reproductive techniques and maternal pre-pregnancy diabetes were confirmed as risk factors. The high rate of different associated anomalies points to the need of performing an early ultrasound screening in all infants born with this disorder.

A Study of Multiple Deliveries in Portugal: Indications of an Iberian Peninsula Pattern

Information on multiple deliveries with regard to Portugal is scarce. Based on data provided by the Portuguese Institute of Statistics (INE), the rates for double and triple deliveries were calculated since 1930. The results obtained show for twins a uniform temporal pattern up to the 1970s. At this time rates decreased, but later they gradually recovered, reaching their maximum level in 2010. For triplets, the highest rates occurred between 1999 and 2002. For the period 1988–2011, the rates of multiple deliveries were related to a set of variables recorded in the INE database on live births. Significant differences (p < .001) between simple and multiple deliveries were obtained for maternal age, parity and marital status. Considering the year when the delivery occurred, significant differences (p < .001) persisted for maternal age regardless of the year. For the type of mating, significance was consistently found since the year 2002 (either by using the marital or the cohabitation criteria), and for parity since 2003. With regard to territorial variation, throughout seven periods between 1930 and 2011, the rates among the 20 administrative Portuguese territories, including the two insular districts of Açores and Madeira, were mostly stable for twinning rates, with a minimum level in 1970–1989. Regarding triplets, the greatest inter-district variation was found after 1980. The results of the Portuguese study on multiple deliveries are interpreted in the context of the Iberian Peninsula based on findings reported for Spain.

Epidemiology of Twin Births in Southeast China: 1993–2005

Recently, there has been a significant increase in the rate of multiple births in most developed countries. However, few population-based studies have been conducted in China regarding the epidemiology of twin births in recent years. We performed a descriptive analysis of twin births from 1993 to 2005 using data from a population-based perinatal care program in southeast China. The twin birth rate in southeast China was 0.65%, and the twin birth rates from 1993 to 2005 fluctuated between 0.60% and 0.70%. During the three periods of 1993–1996, 1997–2000, and 2001–2005, the twin birth rate increased from 0.57% to 0.71% in urban areas (p = .005) and from 0.59% to 0.68% in mothers who had an education level of high school or higher (p = .046). After 2000, the twin birth rate of primiparae 30 years of age and older significantly increased from 0.72% to greater than 1.20%. We concluded that the twin birth rates in southeast China from 1993 to 2005 stayed constant in the overall population but increased in certain subgroups of women, presumably due to increased use of fertility treatment and the development of assisted reproductive technology.

Temporal and Territorial Analysis of Multiple Deliveries in Spain (1900–2006)

Temporal variations in the frequency of multiple maternities in many Western European countries have been described. However, within a single country, regional differences are observed. Urban industrialized regions and rural agricultural areas have experienced in recent decades a distinct decline in multiple deliveries, which in cases have been related to maternal age and parity changes. Research on multiple deliveries in Spain is scarce and none of the studies go back to the beginning of the 20th century or consider regional variation over an extended period of time. The present paper is a yearly study on multiple deliveries in Spain since 1900 including a geographical analysis. Rather than dealing with recent changes in multi-parity, this paper is concerned with Spain's long-term national variation (between 1900 and 2006). The changing pattern of double and triple deliveries was analyzed using data from the Spanish National Statistics Institute (INE). Twinning rates in Spain are low in comparison to those of equivalent periods in other countries, and the minimum rates correspond to the 1980s decade. Results were interpreted by taking into account the influence of age at maternity and reproductive variation up to 1990. A good fit between observed and predicted rates was obtained after the application of models, which besides maternal age and parity, include their interaction. Regarding territorial variability, the values corresponding to southern, northern and insular Spanish provinces are consistent with an earlier reduction of the crude birth rate in the north-east regions and latter in the southern regions and the Canary Islands.

Chilean School-Age Children Twin Registry: Planning, Sampling and Implications

We describe subject recruitment from the University of Chile School-Age Children Twin Registry (REMEUCHI). The research aim of REMEUCHI is to quantify the impact of genetic and environmental factors on scholastic achievement in a multicausal approach. The Ministry of Education of Chile, in collaboration with the Registry Office, provided the list of possible twin pairs graduated from high school in 2004 in Chile's metropolitan region. From a population of 70,065 school-age children who had graduated from high school, 434 possible twin pairs were analyzed. Of these, 327 were twins reared together (75.3% of the 434 possible twins pairs) and born between 1986 and 1987 in Chile (mean age 18 years), and approximately 8% were not twins despite matches on full name and birth data. The rest of the possible twin pairs were probably twins reared apart, since one member of the pair had moved to study in another region of Chile. Zygosity was determined through questionnaires, maternal reports of twin similarities, and by the hospital records of the twins at the time of birth. Three hundred and twenty-seven pairs were identified, where monozygotic (MZ) and dizygotic (DZ) twins represented 46.8% and 53.2% of pairs, respectively, with a DZ/MZ ratio of 1.14. Considering same-sex MZ pairs, the percentage of female pairs was greater (55.6%) than male pairs (44.4%). When DZ pairs were analyzed, 47.7% were of opposite sex, 20.1% were male pairs and 32.2% female pairs. In Chile, these findings represent a baseline study to contribute to the establishment of a national twin registry in the future.

Regional Variations in Trends for Multiple Births: A Population-Based Evaluation in France, 1972–2003

The aim of the study was to assess, using population-based data, trends and regional variations in multiple births during the period of increasing use and changes in practice patterns for infertility treatments. National data for 24,554,977 births (live births and stillbirths) were used, including 569,423 twins during the period 1972 to 2003, and 14,599 triplets for 1984 to 2003. Statistical analyses included age-adjusted hierarchical logistic regression models for twin births and separate analyses for triple, same-sex, and different-sex twin births. Due to confidentiality considerations, the only variable available for adjustment was maternal age. Regionallevel variations were estimated using median odds ratios based on random-intercept hierarchical logistic regression models. Overall, twin births increased from 18.1 per 1000 births (95% confidence interval [CI] 17.9–18.2) in 1972 to 1975 to 29.9 per 1000 (95% CI 29.7–30.1) in 2000 to 2003. Twin births increased progressively across all regions, whereas triple births reached a peak in the early 1990s and decreased thereafter. Trends for both twin and triple births varied significantly across regions. Both trends and regional variations were greater for different-sex as compared with same-sex twin births. Regional variations in the proportion of multiple births increased in the case of twin births and decreased for triple births. Differences in multiple births at the regional level in France were comparable to country-level differences observed across several western and northern European countries. Regional differences in multiple births need to be monitored and used to inform policies aimed at regulating the use of infertility treatments.

Factors Associated with Recent Increase of Multiple Births in Spain

The increased incidence of multiple deliveries in Spain, in addition to changes in age at maternity and parity, is attributed to assisted reproductive treatments, but the relative contribution of the latter to this rise remains uncertain, due to the scarce information provided by clinics practicing those treatments. Population based data (1984–2004), including information on mother's age, nationality, marital status, date of delivery, and the characteristics of each (parity, single or multiple), and sex of newborns were provided by the Spanish Institute of Statistics. Twinning and triplet deliveries relate to maternal age, parity, and nationality. For younger ages (≤ 19, 20–24, 25–29) rates remained constant over time, but for older women (30–34, 35–39, ≥ 40) rates increased after 1994. From 1984 to 2004 the percentage of twins of opposite sex increased from 24.31 to 36.58 per cent. Since 1997, Spanish and non-Spanish mothers differentiate with respect to multiple maternity at ages over 30. In addition to unmarried Spanish women, immigrants constitute a reliable reference group that determines the convenience of segregating information on multiple deliveries respecting origin. The proportion of twins and triplets of opposite sex, maternal age, and parity patterns observed are concordant with a differential access to reproductive treatments depending on the woman's age. The present norm regulating the maximum number of fertilizations per cycle and the demand for these treatments explain the high incidence of multiple deliveries in Spain. A modified logistic curve predicts a stabilization of multiple deliveries, which will probably continue to be high in Spain.

Temporal Trends in the Rates of Multiple Maternities in England and Wales

After a long continuous decrease, the twinning and higher multifetal rates in many developed countries have increased during the last 2 to 3 decades. This change has been attributed to delayed childbearing and to increased use of subfertility treatments, particularly in women over 35 years of age. In this study we analyze how these new trends depend on changes in the effect of maternal age on the rates of multiple maternities. Our study is based on data for England and Wales for the period 1938 to 2003. The temporal variations show a decreasing trend to a trough around 1980 and after that a steady increase. This increase was more marked for higher multifetal rates and was particularly high for quadruplets. Furthermore, we identified changes in the age-specific rates resulting in increased levels for older mothers. These findings are in good agreement with our results from Nordic populations.

Birth outcomes related to informal e-waste recycling in Guiyu, China

To assess the impact of exposure to informal e-waste recycling on birth outcomes. We compared record-based birth outcomes (n=24,493) and levels of cord blood lead (CBPb) (n=531) in Guiyu and a control area in Xiamen. Guiyu births showed significantly higher rates of adverse birth outcomes including stillbirth (4.72% vs. 1.03%), low birth weight (6.12% vs. 4.12%), term low birth weight (3.40% vs. 1.57%), and lower Apgar scores (9.6 vs. 9.9) and mean birth weight (3168 g vs. 3258 g) than did births from the control site, all P<0.01. Regression analysis showed Guiyu had about four times higher risk of stillbirth compared with Xiamen. The median level of CBPb was much higher in neonates of Guiyu than those in the control group (10.78 μg/dL vs. 2.25 μg/dL). Prenatal exposure to informal e-waste recycling related to high rate of adverse birth outcomes, lower Apgar scores and unsafe lead level in cord blood.

Demographic and medical consequences of the postponement of parenthood

BACKGROUND Across the developed world couples are postponing parenthood. This review assesses the consequences of delayed family formation from a demographic and medical perspective. One main focus is on the quantitative importance of pregnancy postponement. METHODS Medical and social science databases were searched for publications on relevant subjects such as delayed parenthood, female and male age, fertility, infertility, time to pregnancy (TTP), fetal death, outcome of medically assisted reproduction (MAR) and mental well-being. RESULTS Postponement of parenthood is linked to a higher rate of involuntary childlessness and smaller families than desired due to increased infertility and fetal death with higher female and male age. For women, the increased risk of prolonged TTP, infertility, spontaneous abortions, ectopic pregnancies and trisomy 21 starts at around 30 years of age with a more pronounced effects >35 years, whereas the increasing risk of preterm births and stillbirths starts at around 35 years with a more pronounced effect >40 years. Advanced male age has an important but less pronounced effect on infertility and adverse outcomes. MAR treatment cannot overcome the age-related decline in fecundity. CONCLUSIONS In general, women have partners who are several years older than themselves and it is important to focus more on the combined effect of higher female and male age on infertility and reproductive outcome. Increasing public awareness of the impact of advanced female and male age on the reproductive outcome is essential for people to make well-informed decisions on when to start family formation.

Twinning across the Developing World

BACKGROUND

Until now, little was known about the variation in incidence of twin births across developing countries, because national representative data was lacking. This study provides the first comprehensive overview of national twinning rates across the developing world on the basis of reliable survey data.

METHODS

Data on incidence of twinning was extracted from birth histories of women aged 15-49 interviewed in 150 Demographic and Health Surveys, held between 1987 and 2010 in 75 low and middle income countries. During the interview, information on all live births experienced by the women was recorded, including whether it was a singleton or multiple birth. Information was available for 2.47 million births experienced by 1.38 million women in a period of ten years before the interview. Twinning incidence was measured as the number of twin births per thousand births. Data for China were computed on the basis of published figures from the 1990 census. Both natural and age-standardized twinning rates are presented.

RESULTS/CONCLUSIONS

The very low natural twinning rates of 6-9 per thousand births previously observed in some East Asian countries turn out to be the dominant pattern in the whole South and South-East Asian region. Very high twinning rates of above 18 per thousand are not restricted to Nigeria (until now seen as the world's twinning champion) but found in most Central-African countries. Twinning rates in Latin America turn out to be as low as those in Asia. Changes over time are small and not in a specific direction.

SIGNIFICANCE

We provide the most complete and comparable overview of twinning rates across the developing world currently possible.

Increasing rates of preterm twin births coincide with improving twin pair survival

OBJECTIVE

To examine trends in twin gestational age over time, with adjustment for potential confounding factors, and to assess twin pair mortality and respiratory support over time.

METHODS

Rates of preterm births, respiratory support, and neonatal mortality were calculated for 21,569 twin pairs born from 1980 to 2005 in Washington State, using birth certificate and hospital discharge data. Fetal death risks were determined on a "per-pair-at-risk" basis.

RESULTS

While the proportion of twins born at 24-31 weeks remained stable at 8%, the proportion born at 32-36 weeks increased from 28% to 48%, and the proportion at 37-42 weeks declined from 64% to 44% (P<0.0001). Controlling individually for a variety of factors, such as maternal age, race, parity, and mode of delivery did not diminish the highly significant trend of increasing preterm births (P<0.0001 for each). Twin pair neonatal mortality decreased significantly through time (P<0.0001); however, the rate of pairs with one or both infants requiring oxygen or ventilation increased significantly through time (P<0.0001). Fetal death risks declined for term twins.

CONCLUSIONS

The proportion of twins born at 32-36 weeks' gestation has increased over time, along with requirement for respiratory support. Twin pair mortality decreased from 1980 to 2005.

Monozygotic twins discordant for neurofibromatosis 1

We present monozygotic twins discordant for the autosomal dominant disorder neurofibromatosis type 1 (NF1). The affected twin was diagnosed with NF1 at age 12, based upon accepted clinical criteria for the disorder. Both twins were re-examined at ages 35 and 57, at which times the unaffected twin continued to show no clinical manifestations of NF1. Short tandem repeat marker (STR) genotyping at 10 loci on chromosome 17 and 10 additional loci dispersed across the genome revealed identical genotypes for the twins, confirming their monozygosity. The affected twin has three children, two of whom also have NF1, while the unaffected twin has two children, both unaffected. Using lymphoblastoid, fibroblast, and buccal cell samples collected from both twins and from other family members in three generations, we discovered a pathogenic nonsense mutation in exon 40 of the NF1 gene. This mutation was found in all cell samples from the affected twin and her affected daughter, and in lymphoblastoid and buccal cells but not fibroblasts from the unaffected twin. We also found a novel non-synonymous change in exon 16 of the NF1 gene that was transmitted from the unaffected mother to both twins and co-segregated with the pathogenic mutation in the ensuing generation. All cells from the twins were heterozygous for this apparent exon 16 polymorphism and for single nucleotide polymorphisms (SNPs) within 2.5 kb flanking the site of the exon 40 nonsense mutation. This suggests that the NF1 gene of the unaffected twin differed in the respective lymphoblastoid cells and fibroblasts only at the mutation site itself, making post-zygotic mutation leading to mosaicism the most likely mechanism of phenotypic discordance. Although the unaffected twin is a mosaic, the distribution of the mutant allele among different cells and tissues appears to be insufficient to cause overt clinical manifestations of NF1.

Predictors of severity in deformational plagiocephaly

Multiple risk factors for deformational plagiocephaly (DP) have been reported. The purpose of this study was to establish the impact of these variables on the severity of this deformity. A prospective cohort study was performed. Parents completed a standardized questionnaire assessing potential risk factors for DP before assessment. Examination included measurement of transcranial difference (TCD; ie, difference in oblique cranial lengths), evaluation of head tilt, and rotational asymmetry. Pearson correlation coefficient, 1-way analysis of variance, and 2-sample t-test were used to quantify the relationship between identified risk factors and TCD. A total of 434 patients with DP were evaluated. Male-to-female ratio was 2:1; mean gestational age was 36.5 weeks. Deformational plagiocephaly was first appreciated at a mean infant age of 6 weeks. A preexisting diagnosis of torticollis was noted in fewer than 50%. Mean TCD was 11.2 mm. Head tilt was documented in 80% of infants, and mean head rotational asymmetry was 16.4 degrees. Deformational plagiocephaly was more severe in multiple birth pregnancies (P < 0.05), males (P < 0.05), infants with a favorite head position (P < 0.01), preexamination diagnosis of torticollis (P < 0.05), and infants with a head tilt (P < 0.05). Lower gestational age (P < 0.05) and greater head rotational asymmetry (P < 0.0001) were found to correlate with DP severity. This study suggests that the relationship between the severity of DP and certain risk factors can be quantified. The presence and degree of cervical imbalance correlate strongly with deformational cranial asymmetry.

Increasing rates of sex-discordant twins no longer correspond to decreasing perinatal mortality rates

OBJECTIVE

To analyze dizygotic twinning rates and outcomes over a 25-year period.

METHODS

Birth and fetal death certificates from 1980-2004 in Washington State, USA, were analyzed retrospectively to find factors associated with the increase in sex-discordant twins through time. "Low" and "high" fertility treatment groups were defined according to demographic traits. Perinatal mortality was defined as fetal or neonatal death of one or both twins and Weinberg's rule was used to estimate mortality for monozygotic and dizygotic pairs.

RESULTS

Controlling simultaneously for maternal age, race, parity, and education did not eliminate the trend of increasing sex-discordant twins from 1992-2004 (M-H chi2 P=0.001). The "low" fertility group had a non-significant decline in sex-discordant twins (M-H chi2 P=0.24), whereas the "high" fertility group had a significant increase (M-H chi2 P=0.001). Perinatal mortality decreased for monozygtic twin pairs throughout the study period, but decreased until the mid-1990s and then increased slightly through 2004 for the dizygotic twin pairs.

CONCLUSION

Advancing maternal age and increasing use of fertility treatments are largely responsible for the increase in dizygotic twins from 1980-2004 and may also be responsible for the stalling of the decline in perinatal mortality rate.

The comparison of twinning rates between urban and rural areas in China

Based on the birth record data from the National Vital Statistics in the 1990 Census of China, the present study analyzed the differences between urban and rural areas on monozygotic (MZ) and dizygotic (DZ) twin rates by maternal age in 1989. The twins by zygosity were calculated with Weinberg's differential method. Results show that the MZ and DZ twinning rates in China were associated with maternal age and that there were substantial differences between urban and rural areas. The MZ twinning rates in urban and rural areas were 2.36 pairs and 2.11 pairs per 1000 deliveries respectively, significantly lower than that in most studied populations. Furthermore, our analysis indicated that MZ twinning rates remained relatively constant for mothers under the age group of 36 to 38 years, but rose over this age group in both areas, albeit with a different slope. The DZ twinning rates were strikingly affected by maternal age, but the age for peak DZ rates was found within the age group of 33 to 35 years. In all maternal age groups except for 24 to 26 years, the DZ twinning rates in urban areas were higher than in rural areas. It remains unclear as to why the DZ twinning rates reversed to reach higher values within the older maternal age groups in China, but it is almost certain that the high twinning rates had nothing to do with in vitro fertilization.