Effect of Fetal Sex on Pregnancy Outcome in Twin Pregnancies

The impact of fetal sex on pregnancy and neonatal outcomes in twin gestation

PURPOSE

Fetal sex is independently associated with pregnancy complications and impacts neonatal outcomes. Evidence suggests that females have an advantage over males, with a better outcome in the perinatal period. In addition, fetal outcome in twin gestations is also related to the intrauterine position of the fetus, such as the first, the presenting or second twin. It has been demonstrated that the neonatal outcome of the second fetus is worse than that of the first fetus. This study aimed to examine the influence of fetal sex on obstetric outcomes in twin pregnancies based on the location of the fetus in the uterus.

METHODS

Retrospective study. Maternal and obstetric outcomes were compared among three groups: male‒male, female‒female, and male‒female groups. Comparisons of neonatal outcomes were performed among the four groups: male A-male B, male A-female B, female A-male B, and female A-female B.

RESULTS

A total of 1073 twin gestations were included, comprising 288 male‒male, 288 female‒female, and 497 male‒female gestations. A greater percentage of neonates admitted to the NICU was observed for male fetuses than for female fetuses. Adverse composite neonatal outcome was more common in the male‒male group than in the female‒male group and in the female‒female group.

CONCLUSION

Twin gestation with a first twin male tends to have worse neonatal outcomes than does twin gestation with a first twin female. The presence of a male co-twin increases the risk of adverse outcomes.

Morbidity and Mortality of Very-Low-Birthweight Twin Infants according to Their Sex and the Sex of the Co-Twin: A Retrospective Cohort Study

INTRODUCTION

The concept of male disadvantage regarding the prognosis of premature newborns was introduced more than half a century ago, and it has been corroborated over time. However, the influence of the sex of one twin on the outcomes of the other has yielded contradictory results.

OBJECTIVE

The aim of the study was to determine if, in twin pregnancies of VLBW infants, the outcomes of one twin are modified by the sex of the co-twin.

METHODS

A multicentre retrospective study of a cohort of infants admitted to the collaborating units of the Spanish SEN1500 neonatal network was conducted. Liveborn VLBW twin infants, from 23+0 to 31+6 weeks of gestational age (GA), admitted from 2011 to 2020 were included. Outborn patients, infants with major congenital anomalies, and cases with only one twin admitted were excluded. The main outcomes were survival until first hospital discharge, survival without moderate or severe bronchopulmonary dysplasia (BPD), survival without major brain damage (MBD), and survival without major morbidity. Incidence rate ratios (IRR) and 95% confidence intervals (CI) were calculated.

RESULTS

2,111 twin pairs were included. Male infants exhibited worse outcomes than females (IRR; 95% CI) regarding survival (0.96; 0.94, 0.98), survival without moderate or severe BPD (0.89; 0.86, 0.93), survival without MBD (0.94; 0.91, 0.97), and survival without major morbidity (0.87; 0.81, 0.93). Differences disappeared when the co-twin was a female infant: survival (1.00; 0.97, 1.03), survival without moderate or severe BPD (0.96; 0.91, 1.01), survival without MBD (0.99; 0.95, 1.04), and survival without major morbidity (0.94; 0.85, 1.03). Results for female infants did not change significantly with co-twin sex.

CONCLUSIONS

Among VLBW twins from 23+0 to 31+6 weeks of GA, male infants have higher risk of morbidity and mortality overall. In cases of pregnancies with different-sex foetuses, males seem to improve their results, while these do not change for females. The underlying mechanism of this influence deserves further investigation.

Characteristics of neonatal herpes simplex central nervous system disease in Australia (1997-2020)

BACKGROUND

Neonatal herpes simplex virus (HSV) central nervous system (CNS) disease can occur in isolation or as part of disseminated infection. We sought to describe neonatal HSV CNS disease in Australia over 24 years.

METHODS

Neonates (≤28 days) with confirmed HSV infection, reported prospectively to the Australian Paediatric Surveillance Unit (1997-2020), were evaluated for HSV CNS disease (laboratory confirmation with clinical evidence of encephalitis, e.g., lethargy, seizures, focal signs; and/or abnormalities on neuroimaging or electroencephalogram), and compared with neonates without CNS disease. CNS-restricted disease was compared with CNS-disseminated disease.

FINDINGS

Of 195 neonates with HSV disease; 87 (45%) had CNS disease (1.29 cases/100,000 live births per year, 95% CI: 1·04-1·59). Neonates with CNS disease were significantly more likely to be male than neonates without CNS disease (60% versus 39%, OR=2·32, 95% CI 1·29-4·18). Of the neonates with CNS disease, those with CNS-restricted disease (52/87, 60%) presented later than neonates with CNS-disseminated disease (35/87, 40%), (mean 12 versus 6 days). Twenty (23%) neonates with CNS disease died, the majority with CNS-disseminated disease (n = 19). Most neonates received aciclovir therapy (94·3%), however five neonates with unrecognised CNS disseminated disease (diagnosed at autopsy) had not been treated. Survivors of CNS disease were significantly more likely to have adverse neurological sequelae, compared with those without CNS disease (30% versus 4%, OR: 9·60, 95% CI: 2·6-35·0).

INTERPRETATION

Male neonates have a higher burden of HSV CNS disease. Despite the use of antiviral agents, morbidity following neonatal HSV CNS disease remains high. Evaluation of adjunctive therapies to improve outcomes is needed.

Male fetuses negatively affect the vitality of the litter and the dam's metabolic and physiological state in multifetal pregnant ewe

In sheep, ~30% of fetuses do not survive till parturition, and 17.7% of the multifetal pregnancies experience partial litter loss (PLL). In humans, multifetal pregnancies are associated with a higher risk of perinatal mortality. Therefore, the objectives were to examine the association between partial litter loss, fetal sex, dam's metabolic and physiological state, and pregnancy outcome in multifetal pregnant ewes. The study includes two parts. The first was a retrospective study, in which we analyzed data of 675 lambings and examined the PLL incidence according to male ratio (MR) for all litter sizes (range 2-6). Lambings were categorized as having a low male ratio (LMR; <50% males) or a high male ratio (LMR; >50% males). In the second part, we monitored 24 ewes from 80 to 138 days in pregnancy every 10 days, and then daily until lambing, by ultrasound scanning for maternal heart rate (HR), and Doppler ultrasound for litter vitality. Blood samples were taken from dams on the days of scanning. Male ratio strongly affected PLL, where the general survival rate (for all lambings) was reduced from 90% in LMR lambings to 85% in HMR lambings. The odds ratio for PLL in HMR vs. LMR litters was 1.82. Birth body weight and the survival rate of female was higher in LMR than HMR lambings, with no differences for male lambs in both parameters. In the second part, dams' HR during the last trimester was 9.4% higher in LMR than in HMR pregnancies, with no differences in fetuses' HR. The plasma glucose and insulin concentrations were not significantly different between groups, but plasma β-hydroxybutyrate and nonesterified fatty acid concentrations were, respectively, 31% and 20% lower in HMR vs. LMR ewes. In conclusion, male fetuses negatively affect pregnancy outcomes and influence dams' metabolic and physiological state in sheep.

Is there an impact of fetal sex in dichorionic discordant twins on placental histopathological abnormalities?

INTRODUCTION

Growth discordancy in dichorionic diamniotic (DCDA) twin gestations is a known complication associated with adverse neonatal outcomes. We aimed to study the differences in placental pathology, in relation to fetal sex, in DCDA twin gestations complicated with growth discordancy.

METHODS

The medical files of all DCDA twin deliveries complicated by growth discordancy between 2010 and 2020 were reviewed. Growth discordance was defined as a gap between twin birthweights > 20%. A comparison was made between female vs. male growth discordant twins. Placental lesions were classified as lesions related to maternal or fetal malperfusion lesions (MVM, FVM), vascular and villous changes, and inflammatory lesions.

RESULTS

Included 174 DCDA twins. Eighty-eight were in the discordant female group and eighty-six in the discordant male group. The groups did not differ in maternal demographics, pregnancy characteristics, and neonatal outcome. The discordant male group had a higher rate of placental MVM lesions as compared to the discordant female group (p = 0.003). The increased rate of placental MVM lesions in the discordant male group compared to the discordant female group did not change whether its co-twin was of similar or opposite sex.

DISCUSSION

Higher rate of MVM lesions characterizes growth discordant male neonates in DCDA twin gestations. This finding could represent a different adaptation of male fetuses to a hostile intrauterine environment.

Association between fetal sex and pregnancy outcomes among women with twin pregnancies: a multicenter cross-sectional study

PURPOSE

To examine the frequency and to what extent fetal sex is associated with pregnancy outcomes among twin pregnancies, stratified by chorionicity.

METHODS

This registry-based multicenter cross-sectional study was conducted using the Japan Society of Obstetrics and Gynecology perinatal database between 2007 and 2016. The sample population was restricted to women with twin pregnancies. The main pregnancy-related outcomes included preterm birth, very preterm birth, extremely preterm birth, preeclampsia, twin-to-twin transfusion syndrome (TTTS), and selective intrauterine growth restriction (s-IUGR). Birth weight, small for gestational age (SGA), and fetal death were also investigated.

RESULTS

The primary analysis was performed based on 37,953 women, including 23,804 women with dichorionic diamniotic (DD) twins and 14,149 women with monochorionic diamniotic (MD) twins. Women with male/male DD twins had a significantly higher risk of preterm birth (adjusted risk ratio [aRR]: 1.07, 95% confidence interval [CI]: 1.03-1.10) and a lower risk of preeclampsia (aRR: 0.74, 95% CI: 0.62-0.88) than women with female/female DD twins. Women with male/male MD twins also had a significantly higher risk of preterm birth (aRR: 1.06, 95% CI: 1.04-1.09) than women with female/female MD twins. Risks of preeclampsia, TTTS, and s-IUGR did not differ by sex among MD pregnancies. Male SGA risk was significantly higher among male/male twins than among male/female DD twins. Among MD twins, risks of SGA and fetal death were significantly higher in male/male fetuses.

CONCLUSIONS

This study demonstrated significant associations between fetal sex and several pregnancy outcomes in twin pregnancies, some of which differed by chorionicity.

Y It Matters—Sex Differences in Fetal Lung Development

Within this review, sex-specific differences in alveolar epithelial functions are discussed with special focus on preterm infants and the respiratory disorders associated with premature birth. First, a short overview about fetal lung development, the challenges the lung faces during perinatal lung transition to air breathing and respiratory distress in preterm infants is given. Next, clinical observations concerning sex-specific differences in pulmonary morbidity of human preterm infants are noted. The second part discusses potential sex-specific causes of pulmonary complications, including pulmonary steroid receptors and local lung steroid metabolism. With regard to pulmonary steroid metabolism, it is important to highlight which steroidogenic enzymes are expressed at which stage during fetal lung development. Thereafter, we review the knowledge concerning sex-specific aspects of lung growth and maturation. Special focus is given to alveolar epithelial Na+ transport as a driver of perinatal lung transition and the sex differences that were noted in this process.

Dosage escalation of antenatal steroids in preterm twin pregnancies does not improve long-term outcome

OBJECTIVES

To analyze long-term effects of antenatal betamethasone (≤16 mg, =24 mg and >24 mg) in preterm twins on infant and childhood morbidity.

METHODS

Retrospective cohort study among 198 preterm twins. Three follow up time points, including a total of 84 outcomes, were evaluated: first neonatal examination after birth and in the neonatal period up to 10 days after birth using data from the clinic charts; examination from the 21st to the 24th month of life and examination from the 60th to the 64th months, using data from copies of the children's examination booklets sent back by the parents. Dosage-dependent and sex-specific long-term effects of antenatal betamethasone treatment on neonatal, infant and early childhood development and morbidity up to 5.3 years of age were analyzed.

RESULTS

Dosage escalation of >24 mg was not associated with improved neonatal, infant or early child hood outcome, independent of twin pair structure. In contrast, higher doses >24 mg were significantly linked to increased rates of congenital infections (OR 5.867, 95% CI 1.895-18.167). Male sex as a factor was obvious for lower rates of apnea-bradycardia-syndrome in neonates, higher rates of no free steps after 15 months in infancy and highest rates of motor clumsiness in early childhood.

CONCLUSIONS

Betamethasone dosage escalation >24 mg in twins born between 23⁺⁵ and 33⁺⁶ weeks of gestation did not improve neonatal, infant or early childhood morbidity. In contrast, higher doses >24 mg total dose resulted in significantly higher rates of congenital infections and are not recommended. For males, 24 mg betamethasone appears to be the preferable dose.

Gestational diabetes and fetal growth in twin compared with singleton pregnancies

BACKGROUND

Gestational diabetes mellitus is associated with accelerated fetal growth in singleton pregnancies but may affect twin pregnancies differently because of the slower growth of twin fetuses during the third trimester of pregnancy and their greater predisposition to fetal growth restriction.

OBJECTIVE

This study aimed to evaluate the association of gestational diabetes mellitus with longitudinal fetal growth in twin pregnancies and to compare this association with that observed in singleton pregnancies.

STUDY DESIGN

This was a retrospective cohort study of all women with a singleton or twin pregnancy who were followed up at a single tertiary referral center between January 2011 and April 2020. Data on estimated fetal weight and individual fetal biometric indices were extracted from ultrasound examinations of eligible women. Generalized linear models were used to model and compare the change in fetal weight and individual biometric indices as a function of gestational age between women with and without gestational diabetes mellitus in twin pregnancies and between women with and without gestational diabetes mellitus in singleton pregnancies. The primary outcome was estimated fetal weight as a function of gestational age. The secondary outcomes were longitudinal growth of individual fetal biometric indices and the rate of small for gestational age and large for gestational age at birth.

RESULTS

A total of 26,651 women (94,437 ultrasound examinations) were included in the analysis: 1881 with a twin pregnancy and 24,770 with a singleton pregnancy. The rate of gestational diabetes mellitus in the twin and singleton groups was 9.6% (n=180) and 7.6% (n=1893), respectively. The estimated fetal weight in singleton pregnancies with gestational diabetes mellitus was significantly higher than that in pregnancies without gestational diabetes mellitus (P<.001) starting at approximately 30 weeks of gestation. The differences remained similar after adjusting for maternal age, chronic hypertension, nulliparity, and neonatal sex (P<.001). In twin pregnancies, fetal growth was similar between pregnancies with and without gestational diabetes mellitus (P=.105 and P=.483 for unadjusted and adjusted models, respectively). The findings were similar to the association of gestational diabetes mellitus with the risk of large for gestational fetuses and the growth of each biometric index. When stratified by type of gestational diabetes mellitus treatment, twin pregnancies with gestational diabetes mellitus was associated with accelerated fetal growth only in the subgroup of women with medically treated gestational diabetes mellitus (P<.001), which represented 12% (n=21) of the twin pregnancy group with gestational diabetes mellitus.

CONCLUSION

In contrast to singleton pregnancies, twin pregnancies with gestational diabetes mellitus is less likely to be associated with accelerated fetal growth. This finding has raised the question of whether the diagnostic criteria for gestational diabetes mellitus and the blood glucose targets in women diagnosed with gestational diabetes mellitus should be individualized for twin pregnancies.

Male Disadvantage in Oxidative Stress-Associated Complications of Prematurity: A Systematic Review, Meta-Analysis and Meta-Regression

A widely accepted concept is that boys are more susceptible than girls to oxidative stress-related complications of prematurity, including bronchopulmonary dysplasia (BPD), retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), intraventricular hemorrhage (IVH), and periventricular leukomalacia (PVL). We aimed to quantify the effect size of this male disadvantage by performing a systematic review and meta-analysis of cohort studies exploring the association between sex and complications of prematurity. Risk ratios (RRs) and 95% CIs were calculated by a random-effects model. Of 1365 potentially relevant studies, 41 met the inclusion criteria (625,680 infants). Male sex was associated with decreased risk of hypertensive disorders of pregnancy, fetal distress, and C-section, but increased risk of low Apgar score, intubation at birth, respiratory distress, surfactant use, pneumothorax, postnatal steroids, late onset sepsis, any NEC, NEC > stage 1 (RR 1.12, CI 1.06–1.18), any IVH, severe IVH (RR 1.28, CI 1.22–1.34), severe IVH or PVL, any BPD, moderate/severe BPD (RR 1.23, CI 1.18–1.27), severe ROP (RR 1.14, CI 1.07–1.22), and mortality (RR 1.23, CI 1.16–1.30). In conclusion, preterm boys have higher clinical instability and greater need for invasive interventions than preterm girls. This leads to a male disadvantage in mortality and short-term complications of prematurity.

Ultrasound for diagnosis of birth weight discordance in twin pregnancies

BACKGROUND

There is a need to standardize monitoring in obstetric research of twin pregnancies. Identification of birth weight discordance (BWD), defined as a difference in the birth weights of twins, is a well-documented phenomenon in twin pregnancies. Ultrasound for the diagnosis of BWD informs complex decision making including whether to intervene medically (via laser photo coagulation) or deliver the twins to avoid fetal morbidities or even death. The question is, how accurate is this measurement?

OBJECTIVES

To determine the diagnostic accuracy (sensitivity and specificity) of ultrasound estimated fetal weight discordance (EFWD) of 20% and 25% using different estimated biometric ultrasound measurements compared with the actual BWD as the reference standard in twin pregnancies.

SEARCH METHODS

The search for this review was performed on 15 March 2019. We searched CENTRAL, MEDLINE (Ovid), Embase (Ovid), seven other databases, conference proceedings, reference lists and contacted experts. There were no language or date restrictions applied to the electronic searches, and no methodological filters to maximize sensitivity.

SELECTION CRITERIA

We selected cohort-type studies with delayed verification that evaluated the accuracy of biometric measurements at ultrasound scanning of twin pregnancies that had been proposed for the diagnosis of estimated BWD, compared to BWD measurements after birth as a reference standard. In addition, we only selected studies that considered twin pregnancies and applied a reference standard for EFWD for the target condition of BWD.

DATA COLLECTION AND ANALYSIS

We screened all titles generated by electronic database searches. Two review authors independently assessed the abstracts of all potentially relevant studies. We assessed the identified full papers for eligibility, and extracted data to create 2 × 2 tables. Two review authors independently performed quality assessment using the QUADAS-2 tool. We excluded studies that did not report data in sufficient detail to construct 2 × 2 tables, and where this information was not available from the primary investigators. We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included 39 eligible studies with a median study sample size of 140. In terms of risk of bias, there were many unclear statements regarding patient selection, index test and use of proper reference standard. Twenty-one studies (53%) were of methodological concern due to flow and timing. In terms of applicability, most studies were of low concern. Ultrasound for diagnosis of BWD in twin pregnancies at 20% cut-off Twenty-two studies provided data for a BWD of 20% and the summary estimate of sensitivity was 0.51 (95% CI 0.42 to 0.60), and the summary estimate of specificity was 0.91 (95% CI 0.89 to 0.93) (8005 twin pregnancies; very low-certainty evidence). Ultrasound for diagnosis of BWD in twin pregnancies at 25% cut-off Eighteen studies provided data using a BWD discordance of 25%. The summary estimate of sensitivity was 0.46 (95% CI 0.26 to 0.66), and the summary estimate of specificity was 0.93 (95% CI 0.89 to 0.96) (6471 twin pregnancies; very low-certainty evidence). Subgroup analyses were possible for both BWD of 20% and 25%. The diagnostic accuracy did not differ substantially between estimation by abdominal circumference and femur length but femur length had a trend towards higher sensitivity and specificity. Subgroup analyses were not possible by sex of twins, chorionicity or gestational age due to insufficient data.

AUTHORS' CONCLUSIONS

Very low-certainty evidence suggests that EFWD identified by ultrasound has low sensitivity but good specificity in detecting BWD in twin pregnancies. There is uncertain diagnostic value of EFWD; this review suggests there is insufficient evidence to support this index as the sole measure for clinical decision making to evaluate the prognosis of twins with growth discordance. The diagnostic accuracy of other measures including amniotic fluid index and umbilical artery Doppler resistive indices in combination with ultrasound for clinical intervention requires evaluation. Future well-designed studies could also evaluate the impact of chorionicity, sex and gestational age in the diagnostic accuracy of ultrasound for EFWD.

Effect of Co-twin Fetal Sex on Fetal Anthropometry and Birth Time in Twin Pregnancies

OBJECTIVE

This study of twin deliveries aimed to examine the effect of fetal sex and fetal sex of the co-twin on fetal anthropometry and length of gestation.

METHODS

Pregnancies were grouped as male/male, male/female, and female/female. Birth weight, head circumference, body length and delivery time of newborns were compared between unlike-sex and like-sex twin pregnancies.

RESULTS

A total of 1028 pregnant women who met the inclusion criteria were enrolled in the study. Of these pregnancies, 32.6% (n = 335) were male/male, 33.4% (n = 343) were male/female, and 34.0% (n = 350) were female/female. The discordant (male/female) newborns had a higher total birth weight than concordant twins (P = 0.015). Compared with male newborns from male/female twin pregnancies, male newborns from male/male pregnancies were found to be 129 grams heavier, 0.7 cm longer, and had a 0.4 cm larger head circumference (P<0.001, P=0.023, and P = 0.039, respectively). Pregnancies with male/female fetuses had statistically significantly longer gestations than pregnancies with male/male and female/female fetuses (P = 0.003 and P = 0.004, respectively). The shortest mean gestation was observed in the male/male group. Male/male pregnancies had a 1.53 times higher risk of preterm delivery than male/female pregnancies and a 1.51 times higher risk than female/female pregnancies (OR 1.53; 95% CI 1.07-2.19 and OR 1.51; 95% CI 1.06-2.16, respectively).

CONCLUSIONS

This study suggests that, in twin pregnancies, birthweight, head circumference, and body length are affected by the sex of the co-twin. Male sex is associated with shorter gestation and male/male twin pregnancies are at higher risk for preterm labour.

Neonatal outcomes of extremely preterm twins by sex pairing: an international cohort study

OBJECTIVE

Infant boys have worse outcomes than girls. In twins, the 'male disadvantage' has been reported to extend to female co-twins via a 'masculinising' effect. We studied the association between sex pairing and neonatal outcomes in extremely preterm twins.

DESIGN

Retrospective cohort study SETTING: Eleven countries participating in the International Network for Evaluating Outcomes of Neonates.

PATIENTS

Liveborn twins admitted at 23-29 weeks' gestation in 2007-2015.

MAIN OUTCOME MEASURES

We examined in-hospital mortality, grades 3/4 intraventricular haemorrhage or cystic periventricular leukomalacia (IVH/PVL), bronchopulmonary dysplasia (BPD), retinopathy of prematurity requiring treatment and a composite outcome (mortality or any of the outcomes above).

RESULTS

Among 20 924 twins, 38% were from male-male pairs, 32% were from female-female pairs and 30% were sex discordant. We had no information on chorionicity. Girls with a male co-twin had lower odds of mortality, IVH/PVL and the composite outcome than girl-girl pairs (reference group): adjusted OR (aOR) (95% CI) 0.79 (0.68 to 0.92), 0.83 (0.72 to 0.96) and 0.88 (0.79 to 0.98), respectively. Boys with a female co-twin also had lower odds of mortality: aOR 0.86 (0.74 to 0.99). Boys from male-male pairs had highest odds of BPD and composite outcome: aOR 1.38 (1.24 to 1.52) and 1.27 (1.16 to 1.39), respectively.

CONCLUSIONS

Sex-related disparities in outcomes exist in extremely preterm twins, with girls having lower risks than boys and opposite-sex pairs having lower risks than same-sex pairs. Our results may help clinicians in assessing risk in this large segment of extremely preterm infants.

Gender variations in neonatal and early infant mortality in India and Pakistan: a secondary analysis from the Global Network Maternal Newborn Health Registry

Background

To determine the gender differences in neonatal mortality, stillbirths, and perinatal mortality in south Asia using the Global Network data from the Maternal Newborn Health Registry.

Methods

This study is a secondary analysis of prospectively collected data from the three south Asian sites of the Global Network. The maternal and neonatal demographic, clinical characteristics, rates of stillbirths, early neonatal mortality (1–7 days), late neonatal mortality (8–28 days), mortality between 29–42 days and the number of infants hospitalized after birth were compared between the male and female infants.

Results

Between 2010 and 2018, 297,509 births [154,790 males (52.03%) and 142,719 females (47.97%)] from two Indian sites and one Pakistani site were included in the analysis [288,859 live births (97.1%) and 8,648 stillbirths (2.9%)]. The neonatal mortality rate was significantly higher in male infants (33.2/1,000 live births) compared to their female counterparts (27.4/1,000, p < 0.001). The rates of stillbirths (31.0 vs. 26.9/1000 births) and early neonatal mortality (27.1 vs 21.6/1000 live births) were also higher in males. However, there were no significant differences in late neonatal mortality (6.3 vs. 5.9/1000 live births) and mortality between 29–42 days (2.1 vs. 1.9/1000 live births) between the two groups. More male infants were hospitalized within 42 days after birth (1.8/1000 vs. 1.3/1000 live births, p < 0.001) than females.

Conclusion

The risks of stillbirths, and early neonatal mortality were higher among male infants than their female counterparts. However, there was no gender difference in mortality after 7 days of age. Our results highlight the importance of stratifying neonatal mortality into early and late neonatal period to better understand the impact of gender on neonatal mortality. The information from this study will help in developing strategies and identifying measures that can reduce differences in sex-specific mortality.

The COVID-19 stress may influence on the sex ratio at birth

The ratio of boys to girls (sex ratio) at birth (SRB) is about 1.01-1.05 in most populations and is influenced by various factors, such as maternal stress, maternal inflammation, and endocrine disruption. Male fetus is biologically weaker and more vulnerable to prenatal events than female fetuses. Hence, premature death (and consequently decline the SRB) is higher in boys than girls. The recent coronavirus disease 2019 (COVID-19) has been known to have a variety of stressful and psychological impacts. This stress may consequently enhance maternal inflammation, pregnancy complication, and fetal loss. Also, male fetuses have more adverse outcomes than female fetuses among asymptomatic pregnant women with SARS-Cov-2 infection. Inasmuch as the male fetus are more vulnerable to prenatal events and premature death, it is proposed that the SRB can decline in pregnant women following the COVID-19 stress. However, future studies are needed to define the impact of the COVID-19 on SRB rate.

The association of sex of co-twin and birth size in twins born in Yucatan, Mexico between 2008 and 2017

Background: Birth measures of twins are potentially influenced by sex of co-twin.Aim: To analyse the association between sex of co-twin and birth weight, length and ponderal index in twin infants from Yucatan, Mexico.Subjects and methods: A total of 2057 twin pairs born during 2008-2017 were analysed. Female-female (F-F), male-male (M-M) and male-female (M-F) twin pair types were defined. Multiple linear regression models were used to analyse the association of (1) being female from M-F pairs and birth measures among overall female infants (M-F and F-F), and (2) being male from M-F pairs and birth measures among overall male infants (M-F and M-M). The length of gestation and mothers' age and level of education were used as covariates.Results: Models showed that being male from M-F pairs was associated with increases of 81 g in birth weight and 0.61 cm in length, compared to males from M-M pairs, and being female from opposite-sex pairs was associated with increases of 0.36 cm in length, compared to females from same-sex pairs.Conclusions: Males from M-F pairs show greater birth size than males from same-sex pairs, which supports the hypothesis that birth measures of twins are influenced by sex of the co-twin.

Intrapartum hypoxia and sexual dimorphism in adverse perinatal outcomes

OBJECTIVES

The aim of this study is to evaluate whether markers of intrapartum hypoxia differ according to sex, and if this could explain the increased risk of adverse perinatal outcomes in males.

STUDY DESIGN

This is a retrospective observational cohort study of non-anomalous, singleton deliveries >36 completed weeks' gestation at a UK teaching hospital over a 4.5 year period. Absent or incomplete cord gas results were excluded and the remaining data were validated according to an established method. The relations between sex and both arterial pH and a composite variable, 'fetal distress' (cases in which operative delivery or caesarean section were undertaken for presumed fetal compromise), were examined using independent samples t-test and Chi-square test. Odds ratios with 95 % confidence intervals were calculated to describe the relation between fetal sex and intermediate-term adverse outcomes. Binary logistic regression was performed to generate odds ratios (with 95 % confidence intervals) adjusted for arterial pH and fetal distress. This was repeated to adjust for labor and induction of labor.

RESULTS

There were eligible 8758 cases, of which 4655 were male and 4103 female, from a total of 39,148 deliveries during the study period. Neonatal unit admission (OR 1.54, 95 % CI; 1.31-1.80), renal impairment (OR 1.63, 95 % CI; 1.15-2.32), neurological impairment (OR 1.73, 95 % CI; 1.06-2.84) and a composite adverse outcome (OR 1.73, 95 % CI; 1.29-2.33) were all more likely in males, even after adjusting for labor and induction of labor, both of which were more likely males. The mean cord arterial pH of males was lower (7.23 vs 7.24, P = 0.019) although they were not more likely to be acidemic with a pH <7.0 (males 43 (0.92 %) vs females 41 (1.00 %), P = 0.717), and males were also more likely to have fetal distress (834 (17.9 %) vs 588 (14.3 %), P = <0.001). Being male remained associated with adverse outcomes despite adjustment for arterial pH and fetal distress.

CONCLUSION

Despite a lower mean cord arterial pH and greater incidence of fetal distress in males, intrapartum hypoxia does not account for their worse neonatal outcomes.

Newborn gender as a predictor of neonatal outcome in mixed gender twins born with very low birth weight

Background

Most studies have revealed that the incidence of morbidity and mortality of preterm male infants is greater than that of preterm female infants. Recently, conflicting outcomes have been reported regarding mixed-gender twins. The aim of this study was to estimate the association between gender and outcome in newborn twins of different gender.

Methods

We conducted a retrospective review of mixed-gender twins weighing < 1500 g that were born at Shamir Medical Center (Assaf Harofeh) between the years 1995 and 2016 (158 newborns). The incidence of morbidity and mortality until discharge from the hospital were evaluated while looking at gender differences.

Results

No significant differences were found in neonatal mortality or morbidity between females and males from different-gender twins. Even after considering confounding variables (gestational age, birth weight & birth order) in linear and logistic regression models, no significant differences were found between the genders.

Conclusions

Our study suggests that there are no significant differences in neonatal mortality or morbidity among different-gender twins. Our results support the need for further studies.

SMFM Special Statement: State of the science on multifetal gestations: unique considerations and importance

We sought to review the state of the science for research on multiple gestations. A literature search was performed with the use of PubMed for studies to quantify the representation of multiple gestations for a sample period (2012-2016) that were limited to phase III and IV randomized controlled trials, that were written in English, and that addressed at least 1 of 4 major pregnancy complications: fetal growth restriction or small-for-gestational-age fetus, gestational diabetes mellitus, preeclampsia, and preterm delivery. Of the 226 studies that are included in the analysis, multiple pregnancies were most represented in studies of preterm delivery: 17% of trials recruited both singleton and multiple pregnancies; another 18% of trials recruited only multiple pregnancies. For trials that studied preeclampsia, fetal growth restriction, and gestational diabetes mellitus, 17%, 8%, and 2%, respectively, recruited both singleton and multiple gestations. None of the trials on these 3 topics were limited to women with a multiple pregnancy. Women with a multiple pregnancy are at risk for complications similar to those of women with singleton pregnancies, but their risk is usually higher. Also, the pathophysiologic condition for some complications differs in multiple gestations from those that occur in singleton gestations. Conditions that are unique to multiple pregnancies include excess placenta, placental crowding or inability of the uteroplacental unit to support the normal growth of multiple fetuses, or suboptimal placental implantation sites with an increased risk of abnormal placental location. Other adverse outcomes in multiple gestations are also influenced by twin-specific risk factors, most notably chorionicity. Although twins have been well represented in many studies of preterm birth, these studies have failed to identify adequate predictive tests (short cervical length established over 2 decades ago remains the single best predictor), to establish effective interventions, and to differentiate the underlying pathophysiologic condition of twin preterm birth. Questions about fetal growth also remain. Twin growth deviates from that of singleton gestations starting at approximately 32 weeks of gestation; however, research with long-term follow-up is needed to better distinguish pathologic and physiologic growth deviations, which include growth discordance among pairs (or more). There are virtually no clinical trials that are specific to twins for gestational diabetes mellitus or preeclampsia, and subgroups for multiple pregnancies in existing trials are not large enough to allow definite conclusions. Another important area is the determination of appropriate maternal nutrition or micronutrient supplementation to optimize pregnancy and child health. There are also unique aspects to consider for research design in multiple gestations, such as designation and tracking of the correct fetus prenatally and through delivery. The correct statistical methods must be used to account for correlated data because multiple fetuses share the same mother and intrauterine environment. In summary, multiple gestations often are excluded from research studies, despite a disproportionate contribution to national rates of perinatal morbidity, mortality, and health-care costs. It is important to consider the enrollment of multifetal pregnancies in studies that target mainly women with singleton gestations, even when sample size is inadequate, so that insights that are specific to multiple gestations can be obtained when results of smaller studies are pooled together. The care of pregnant women with multiple gestations presents unique challenges; unfortunately, evidence-based clinical management that includes the diagnosis and treatment of common obstetrics problems are not well-defined for this population.

Sex-specific influence of the vacuolar adenosine triphosphatase a2 isoform on outcome in twin pregnancies

PROBLEM

The influence of fetal sex on immune responses in multifetal pregnancies remains incompletely elucidated. The a2 isoform of vacuolar adenosine triphosphatase (a2V) is expressed on the cell membrane of maternal lymphoid cells and contributes to down-regulation of pro-inflammatory immune responses during gestation. The association between fetal sex and a2V expression on peripheral blood mononuclear cells (PBMCs) from mothers with twin gestations was assessed.

METHOD OF STUDY

Patients in this prospective study were 93 women with twin pregnancies in their mid-second or early third trimester-27 with two male, 30 with two female and 36 with one male and one female fetus. PBMCs were isolated and a2V was measured by ELISA in cell lysates. Demographic and clinical data were subsequently obtained and correlations between a2V and fetal sex, birthweight and pregnancy outcome were assessed by the Mann-Whitney and Spearman rank correlation tests.

RESULTS

The mean a2V level was highest when both fetuses were male (2.0 ng/mL) and lowest when both were female (1.5 ng/mL; P = 0.0184). Only when both fetuses were female did the a2V concentration negatively correlate with birthweight of the 1st (P = 0.0011) and 2nd (P = 0.0044) born fetus and with gestational age at delivery (P = 0.0018). There were no associations between a2V and these outcomes in male only or mixed twin pregnancies.

CONCLUSION

We conclude that the a2V-mediated regulation of maternal immunity during twin pregnancies is influenced by fetal sex.

Gender disparities in preterm neonatal outcomes

AIM

From birth to old age, males generally have poorer disease outcomes compared to females. Preterm infants display a marked gender disparity in disease outcomes, and the underlying mechanisms are not well delineated. Our aim was to review the literature on clinical outcomes between preterm infants of different genders and discuss the potential mechanisms underlying the differences observed.

METHODS

A literature review was undertaken for experimental and clinical research related to gender differences in preterm outcomes.

RESULTS

Preterm male infants appear to have consistently worse outcomes compared to females, and the aetiology of these differences, while mostly undetermined, is likely multifactorial.

CONCLUSION

The male disadvantage in preterm outcomes is likely multifactorial with hormonal, genetic and immunological differences likely playing key roles. Gender is an important variable in preterm outcome and should be considered when designing clinical and experimental research.

Birth size and gestational age in opposite-sex twins as compared to same-sex twins: An individual-based pooled analysis of 21 cohorts

It is well established that boys are born heavier and longer than girls, but it remains unclear whether birth size in twins is affected by the sex of their co-twin. We conducted an individual-based pooled analysis of 21 twin cohorts in 15 countries derived from the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), including 67,850 dizygotic twin individuals. Linear regression analyses showed that boys having a co-twin sister were, on average, 31 g (95% CI 18 to 45) heavier and 0.16 cm (95% CI 0.045 to 0.274) longer than those with a co-twin brother. In girls, birth size was not associated (5 g birth weight; 95% CI −8 to −18 and −0.089 cm birth length; 95% CI −0.202 to 0.025) with the sex of the co-twin. Gestational age was slightly shorter in boy-boy pairs than in boy-girl and girl-girl pairs. When birth size was standardized by gestational age, the magnitude of the associations was attenuated in boys, particularly for birth weight. In conclusion, boys with a co-twin sister are heavier and longer at birth than those with a co-twin brother. However, these differences are modest and partly explained by a longer gestation in the presence of a co-twin sister.

Maternal anemia during pregnancy and slightly higher risk of asthma in male offspring

AIM

We aimed to determine whether maternal hemoglobin levels or anemia during pregnancy are associated with the development of asthma among offspring.

METHODS

Data were retrieved from the birth register database of Kuopio University Hospital between 1989 and 2007 (n = 38 381). Hemoglobin levels were measured during three trimesters of pregnancy and anemia was defined according to the World Health Organization criteria. The prevalence of asthma was determined from the register of reimbursement for medication for asthma at the Finnish Social Security Institution. Cox proportional hazard regression analysis was performed to evaluate the possible associations between prenatal factors and development of asthma ever.

RESULTS

A total of 8198 (21.4%) women had anemia at some stage of pregnancy. Mild maternal anemia during the first trimester was associated with an increased risk of asthma among male offspring (adjusted hazard ratio, 1.46; 95% confidence interval, 1.11-1.94) compared with those with normal maternal hemoglobin levels. This finding remained significant also after applying the Bonferroni correction.

CONCLUSION

Male offspring with maternal anemia during the first trimester of pregnancy had significantly more asthma ever than the offspring of women with normal hemoglobin levels during pregnancy. These findings were not strong but suggest possible sex-specific effects of maternal health on prenatal programming and future risk of asthma.

Gender Differences in Infant Mortality and Neonatal Morbidity in Mixed-Gender Twins

In the present study, we aimed to explore gender differences in infant mortality and neonatal morbidity in mixed-gender twin pairs. Data were obtained from the US National Center for Health Statistics Linked Birth-Infant Death Cohort. A total of 108,038 pairs of mixed-gender twins were included in this analysis. Among the mixed-gender twins, no significant difference in the odds of fetal mortality between male twins (1.05%) and female co-twins (1.04%). However, male twins were at increased odds of neonatal mortality (adjusted OR 1.59; 95% CI 1.37, 1.85) and overall infant mortality (adjusted OR 1.43; 95% CI 1.27, 1.61) relative to their female co-twins. Congenital abnormalities (adjusted OR 1.38; 95% CI 1.27, 1.50) were identified significantly more frequently in male than female twins. Moreover, increased odds of having low 5-minute Apgar score (<7) (adjusted OR 1.15; 95% CI 1.05, 1.26), assistant ventilation >30 minutes (adjusted OR 1.31; 95% CI 1.17, 1.47), and respiratory distress syndrome (adjusted OR 1.45; 95% CI 1.26, 1.66) were identified in male twins relative to their female counterparts. The results of our study indicated that in mixed-gender twin pairs, the odds of infant mortality and neonatal morbidity were higher in male twins than their female co-twins.

Does the sex of one's co-twin affect height and BMI in adulthood? A study of dizygotic adult twins from 31 cohorts

Background

The comparison of traits in twins from opposite-sex (OS) and same-sex (SS) dizygotic twin pairs is considered a proxy measure of prenatal hormone exposure. To examine possible prenatal hormonal influences on anthropometric traits, we compared mean height, body mass index (BMI), and the prevalence of being overweight or obese between men and women from OS and SS dizygotic twin pairs.

Methods

The data were derived from the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) database, and included 68,494 SS and 53,808 OS dizygotic twin individuals above the age of 20 years from 31 twin cohorts representing 19 countries. Zygosity was determined by questionnaires or DNA genotyping depending on the study. Multiple regression and logistic regression models adjusted for cohort, age, and birth year with the twin type as a predictor were carried out to compare height and BMI in twins from OS pairs with those from SS pairs and to calculate the adjusted odds ratios and 95% confidence intervals for being overweight or obese.

Results

OS females were, on average, 0.31 cm (95% confidence interval (CI) 0.20, 0.41) taller than SS females. OS males were also, on average, taller than SS males, but this difference was only 0.14 cm (95% CI 0.02, 0.27). Mean BMI and the prevalence of overweight or obesity did not differ between males and females from SS and OS twin pairs. The statistically significant differences between OS and SS twins for height were small and appeared to reflect our large sample size rather than meaningful differences of public health relevance.

Conclusions

We found no evidence to support the hypothesis that prenatal hormonal exposure or postnatal socialization (i.e., having grown up with a twin of the opposite sex) has a major impact on height and BMI in adulthood.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-017-0134-x) contains supplementary material, which is available to authorized users.

Twins less frequent than expected among male births in risk averse populations

Male twin gestations exhibit higher incidence of fetal morbidity and mortality than singleton gestations. From an evolutionary perspective, the relatively high rates of infant and child mortality among male twins born into threatening environments reduce the fitness of these gestations, making them more vulnerable to fetal loss. Women do not perceive choosing to spontaneously abort gestations although the outcome may result from estimates, made without awareness, of the risks of continuing a pregnancy. Here, we examine whether the non-conscious decisional biology of gestation can be linked to conscious risk aversion. We test this speculation by measuring the association between household surveys in Sweden that gauge financial risk aversion in the population and the frequency of twins among live male births. We used time-series regression methods to estimate our suspected associations and Box-Jenkins modeling to ensure that autocorrelation did not confound the estimation or reduce its efficiency. We found, consistent with theory, that financial risk aversion in the population correlates inversely with the odds of a twin among Swedish males born two months later. The odds of a twin among males fell by approximately 3.5% two months after unexpectedly great risk aversion in the population. This work implies that shocks that affect population risk aversion carry implications for fetal loss in vulnerable twin pregnancies.

Assessment of Frequency of Twin Pregnancy and Neonatal Outcome in Deliveries of Mo'tazedi Hospital, Kermanshah in 2004-2007

INTRODUCTION

Twin pregnancy is a high-risk pregnancy with different prevalences in different regions of the world which is on the rise due to growing use of assisted reproductive technology. The objective of this study is to determine the frequency of twin pregnancy and the neonatal outcome of these pregnancies.

MATERIALS AND METHODS

This is a descriptive-analytic study conducted in 2004-2007 in Mo'tazedi Hospital, Kermanshah on 142 twin deliveries as well as the singleton deliveries before and after twin pregnancy as the control group. The required information, including maternal age, gestational age, newborn's gender, presentation of twins, birth weight, Apgar score, fetal anomalies, and neonatal mortality were extracted from medical files and analyzed statistically.

FINDINGS

After assessment of 29,438 deliveries performed from 2004 to 2007, the frequency of twin pregnancy was found out to be 1 in 208 cases (48 %). The mean age of mothers was higher in twin pregnancies. The mean gestational age of twin pregnancy was 34.3 weeks. Apgar score and neonatal weight were significantly lower in twin pregnancy compared to singleton pregnancy (p < 0.001). Furthermore, visible anomalies and mortality were significantly higher in neonates born to twin pregnancies compared to singleton pregnancies (p < 0.0001 and p = 0.009, respectively). The ratio of male to female neonates was 1.

CONCLUSION

This study indicated that twin pregnancy is a high-risk condition and entails greater neonatal complications compared to singleton pregnancy. Therefore, it is recommendable to have greater perinatal care and perform deliveries in well-equipped centers under supervision of an obstetrician.

Relationship of mode of conception and sex concordance with mortality/morbidity in preterm twins

OBJECTIVE

To assess the association of mode of conception and sex concordance with neonatal outcomes in very preterm twins.

STUDY DESIGN

Twin pairs born at gestational age ≤ 32 weeks and admitted to a Level 3 neonatal intensive care unit (NICU) in 2010-2011 were retrospectively identified from the Canadian Neonatal Network™ database. A composite outcome representing neonatal mortality or any severe morbidity (intraventricular hemorrhage grades ≥ 3 or periventricular leukomalacia, retinopathy of prematurity stages ≥ 3, bronchopulmonary dysplasia, or necrotizing enterocolitis stages ≥ 2) was compared between twins conceived using assisted reproduction technologies (ARTs) or spontaneously (SP), and tested for association with sex concordance in individual-level and pair-wise multivariable logistic regression analyses.

RESULTS

Study subjects included 1,508 twins from 216 ART (53 [25%] male-male, 104 [48%] male-female, and 59 [27%] female-female) and 538 SP (192 [36%] male-male, 123 [23%] male-female, and 223 [41%] female-female) pairs. No statistically significant association was detected between mode of conception and the composite outcome of mortality/morbidities. The composite outcome was significantly higher in same-sex than in opposite-sex twins (OR = 1.68; 95% CI = [1.09, 2.59]). This relationship was most pronounced in ART pairs (OR = 2.25; 95% CI = [1.02, 4.98]), with increased rates in one or both twins from male-male versus opposite-sex ART pairs (OR = 3.0; 95% CI = [1.07, 8.36]).

CONCLUSION

Same-sex pairing was associated with higher mortality/morbidities in very preterm twins admitted to the NICU, and can be used in clinical practice to identify twins at higher risk of adverse neonatal outcomes.

Risk factors for acute respiratory morbidity in moderately preterm infants

BACKGROUND

Infants born preterm account for a substantial part of neonatal morbidity, with acute respiratory disorders being a dominating clinical problem. Whereas focus in recent studies has been on extremely and very preterm infants, less is known about contemporary rates and risk factors for acute respiratory morbidity in moderately and late preterm infants. The objective of this population-based Swedish study was to establish rates for different acute respiratory diseases in moderately preterm infants, and to identify maternal, obstetric and neonatal risk factors for the two most common diagnoses, transient tachypnoea of the newborn (TTN) and respiratory distress syndrome (RDS).

METHODS

The study included 4679 moderately preterm [gestational age (GA): 30 to 34 weeks], 15 036 late preterm infants (GA 35 to 36 weeks) and 451 479 term infants (GA: 37 to 41 weeks). All infants were born in 2004-2008.

RESULTS

In moderately preterm infants, risk factors for TTN in multivariable analyses were multiparity, caesarean section before and after onset of labour, male sex, Apgar score 4-6 at 5 min and lower GA. Risk factors for RDS were multiparity, caesarean section before and after onset of labour, male sex, Apgar score <7 at 5 min and lower GA. Preterm rupture of membranes, antenatal corticosteroid treatment and being small for gestational age reduced the risk of RDS.

CONCLUSION

We conclude that acute respiratory morbidity in moderately preterm infants is common and predicted by multiparity, caesarean section, low Apgar score and male sex.

Fetal gender and pregnancy outcomes in Libya: a retrospective study

Objective

The relationship between pregnancy outcomes and fetal gender is well reported from different areas in the world, but not from Africa. In this study, we try to understand whether the recorded phenomenon of association of adverse pregnancy outcomes with a male fetus applies to our population.

Materials and methods

A total of 29,140 patient records from 2009 and 2010 were retrieved from Aljalaa Maternity Hospital, Tripoli, Libya. Analysis was carried out to find the correlation between fetal gender and different pregnancy outcomes.

Results

A male fetus was associated with an increased incidence of gestational diabetes mellitus (odds risk 1.4), preterm delivery (6.7% for males, 5.5% for females, odds risk 1.24), cesarean section (23.9% for males, 20% for females, odds risk 1.25), and instrumental vaginal delivery (4.4% for males, 3.1% for females, odds risk 1.48), p<0.005. Preeclampsia was more frequent among preterm females and postterm males, p<0.005. It was also more frequent in male-bearing primigravids, p<0.01.

Conclusion

We confirm the existence of an adverse effect of a male fetus on pregnancy and labor in our population. We recommend further research to understand the mechanisms and clinical implications of this phenomenon.

Fetal sex and preterm birth

Rates of preterm birth vary between different populations and ethnic groups. Epidemiologic studies have suggested that the incidence of preterm birth is also higher in pregnancies carrying a male fetus; the male:female difference is greater in earlier preterm pregnancy. Placental or chorion trophoblast cells from pregnancies with a male fetus produced more pro-inflammatory TNFα in response to LPS stimulation and less anti-inflammatory IL-10 and granulocyte colony stimulating factor (G-CSF) than cells from pregnancies with a female fetus, more prostaglandin synthase (PTGS-2) and less prostaglandin dehydrogenase (PGDH). These results suggest that in the presence of a male fetus the trophoblast has the potential to generate a more pro-inflammatory environment. Maturation of the fetal hypothalamic-pituitary-adrenal axis and expression of placental genes, particularly 11β hydroxysteroid dehydrogenase-2 are also expressed in a sex dependent manner, consistent with the sex-biasing influences on gene networks. Sex differences in these activities may affect clinical outcomes of pre- and post-dates pregnancies and fetal/newborn wellbeing. These factors need consideration in studies of placental function and in the development of personalized strategies for the diagnosis of preterm labor and postnatal health.

Fetal sex pairing and adverse perinatal outcomes in twin gestations

PURPOSE

To assess the association between fetal sex pairing in twin pregnancies and adverse perinatal and infant outcomes.

METHODS

A retrospective cohort study of 9770 infants from 4885 twin pregnancies delivered in 2007 was conducted with a statewide hospital discharge database for Texas. Log-binomial regression models based on generalized estimating equations were used to calculate relative risks (RR) and 95% confidence intervals (95% CI) for the following dichotomous outcomes: breech presentation, hospital mortality, intrauterine growth restriction (IUGR), low birth weight, prolonged length of stay (>4 days), receipt of mechanical ventilation, and respiratory distress syndrome (RDS).

RESULTS

The sample was composed of 4918 females and 4852 males. An approximately equal number of infants were from a female-female pregnancy (n = 3270), mixed-sex pregnancy (n = 3296), and a male-male pregnancy (n = 3204). Twins of either sex from mixed-sex pairs were 45% less likely to die in the hospital compared with females from a female-female pregnancy (RR, 0.55, 95% CI, 0.31-0.98). Males from a male-male pair were 33% less likely than females from female-female pairs to experience IUGR (RR, 0.67; 95% CI, 0.53-0.83). The incidence of RDS was significantly increased in males from male-male twin pairs versus females from female-female pairs (RR, 1.21; 95% CI, 1.05-1.41).

CONCLUSIONS

Male infants from male-male twin pairs were more likely to develop RDS and be placed on a ventilator but less likely to experience IUGR than female infants from female-female pairs.

Contribution of twin-to-twin transfusion syndrome to preterm birth among monochorionic biamniotic and bichorionic biamniotic twin pregnancies

AIMS

To determine the contribution of twin-to-twin transfusion syndrome (TTTS) to preterm birth (PTB) at <37 weeks of gestation among Japanese twin pregnancies.

METHODS

An observational study using 3241 MC-BA (monochorionic biamniotic) and 6581 BC (bichorionic biamniotic) twin pregnancies. We focused on TTTS, preterm premature rupture of membranes (PPROM), pregnancy-induced hypertension (PIH), and fetal sex as possible causes of PTB.

RESULTS

PTB was more common in MC-BA than in BC twin pregnancies (66.9% vs. 57.6%, P<0.0001) whereas PTB after PPROM (8.0% vs. 10.0%) and PIH (5.7% vs. 5.9%) was not. PTB after TTTS occurred in 7.3% of women with MC-BA twins. PTB was significantly more common for male-male pairs than for female-female pairs among both MC-BA (69.2% vs. 64.7%) and BC (59.6% vs. 56.3%) twins.

CONCLUSION

The elevated risk of PTB among MC-BA twins could be explained by the occurrence of TTTS.

IUGR differentially alters MeCP2 expression and H3K9Me3 of the PPARγ gene in male and female rat lungs during alveolarization

Intrauterine growth restriction (IUGR) increases the risk of postnatal lung disease, with males more affected. In rat lungs, IUGR impairs alveolarization in conjunction with altered expression of peroxisome proliferator-activated receptor gamma (PPARγ). In non-lung cells, PPARγ transcription is regulated in part by the epigenetic modifying enzyme, and the methyl CpG binding protein 2 (MeCP2). However, it is unknown if IUGR affects MeCP2 expression or its interaction with PPARγ in the rat lung during alveolarization. In this study, we hypothesized that the rat lung would be characterized by the presence of MeCP2 short and long mRNA transcripts, MeCP2 protein isoforms, and the MeCP2 regulatory micro RNA, miR132. We further hypothesized that IUGR would, in a gender-specific manner, alter the levels of MeCP2 components in association with changes in PPARγ mRNA, MeCP2 occupancy at the PPARγ promoters, and PPARγ histone 3 lysine 9 trimethylation (H3K9Me3). To test these hypotheses, we used a well-characterized rat model of uteroplacental insufficiency-induced IUGR. We demonstrated the presence of MeCP2 mRNA, protein, and miR132 in the rat lung throughout alveolarization. We also demonstrated that IUGR alters MeCP2 expression and its interaction with PPARγ in a gender-divergent manner. We conclude that IUGR induces gender-specific alterations in the epigenetic milieu in the rat lung. We speculate that in the IUGR rat lung, this altered epigenetic milieu may predispose to gender-specific alterations in alveolarization.

IUGR decreases PPARγ and SETD8 Expression in neonatal rat lung and these effects are ameliorated by maternal DHA supplementation

Intrauterine growth restriction (IUGR) is associated with altered lung development in human and rat. The transcription factor PPARγ, is thought to contribute to lung development. PPARγ is activated by docosahexanoic acid (DHA). One contribution of PPARγ to lung development may be its direct regulation of chromatin modifying enzymes, such as Setd8. In this study, we hypothesized that IUGR would result in a gender-specific reduction in PPARγ, Setd8 and associated H4K20Me levels in the neonatal rat lung. Because DHA activates PPARγ, we also hypothesized that maternal DHA supplementation would normalize PPARγ, Setd8, and H4K20Me levels in the IUGR rat lung. We found that IUGR decreased PPARγ levels, with an associated decrease in Setd8 levels in both male and female rat lungs. Levels of the Setd8-dependent histone modification, H4K20Me, were reduced on the PPARγ gene in both males and females while whole lung H4K20Me was only reduced in male lung. Maternal DHA supplementation ameliorated these effects in offspring. We conclude that IUGR decreases lung PPARγ, Setd8 and PPARγ H4K20Me independent of gender, while decreasing whole lung H4K20Me in males only. These outcomes are offset by maternal DHA. We speculate that maintenance of the epigenetic milieu may be one role of PPARγ in the lung and suggests a novel benefit of maternal DHA supplementation in IUGR.

Heritability of apnea of prematurity: a retrospective twin study

BACKGROUND

Apnea of prematurity (AOP) is a disturbance in respiratory rhythm defined by idiopathic pauses in breathing that reduce blood oxygen levels and/or heart rate. It is a major clinical problem among preterm infants.

OBJECTIVES

The primary goal of this study was to estimate the genetic susceptibility to AOP in a cohort of preterm twins. A secondary aim was to identify risk factors associated with AOP in this cohort.

METHODS

A single-center, retrospective study (2000-2008) was performed by using data from 317 premature twin pairs (<36 weeks' gestational age). Heritability estimates were determined by comparing intrapair AOP concordance between 56 monozygotic and 161 dizygotic twin pairs by using structural equation modeling. Risk factors of AOP among a cohort of 543 premature twins were assessed by using mixed-effects logistic regression.

RESULTS

The heritability of AOP was 87% (95% confidence interval [CI]: 0.64-0.97) among same-gender twins. A gender-dependent model revealed that genetic factors accounted for 99% of the variance in male twins (95% CI: 0.89-1.00) and 78% of the variance in female twins (95% CI: 0.49-0.94). Significant risk factors for AOP were low gestational age (P<.001), cesarean delivery (P=.017), and conception through assisted reproductive technologies (P=.008).

CONCLUSIONS

These findings suggest that AOP has an important genetic basis underlying this developmental-related disorder of respiratory control. Future genomic studies may provide information on pathophysiological mechanisms that underlie AOP.

Impact of environmental chemicals on lung development

BACKGROUND

Disruption of fundamental biologic processes and associated signaling events may result in clinically significant alterations in lung development.

OBJECTIVES

We reviewed evidence on the impact of environmental chemicals on lung development and key signaling events in lung morphogenesis, and the relevance of potential outcomes to public health and regulatory science .

DATA SOURCES

We evaluated the peer-reviewed literature on developmental lung biology and toxicology, mechanistic studies, and supporting epidemiology.

DATA SYNTHESIS

Lung function in infancy predicts pulmonary function throughout life. In utero and early postnatal exposures influence both childhood and adult lung structure and function and may predispose individuals to chronic obstructive lung disease and other disorders. The nutritional and endogenous chemical environment affects development of the lung and can result in altered function in the adult. Studies now suggest that similar adverse impacts may occur in animals and humans after exposure to environmentally relevant doses of certain xenobiotics during critical windows in early life. Potential mechanisms include interference with highly conserved factors in developmental processes such as gene regulation, molecular signaling, and growth factors involved in branching morphogenesis and alveolarization.

CONCLUSIONS

Assessment of environmental chemical impacts on the lung requires studies that evaluate specific alterations in structure or function-end points not regularly assessed in standard toxicity tests. Identifying effects on important signaling events may inform protocols of developmental toxicology studies. Such knowledge may enable policies promoting true primary prevention of lung diseases. Evidence of relevant signaling disruption in the absence of adequate developmental toxicology data should influence the size of the uncertainty factors used in risk assessments.