Fetal sex pairing and adverse perinatal outcomes in twin gestations

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.

Sex at the interface: the origin and impact of sex differences in the developing human placenta

The fetal placenta is a source of hormones and immune factors that play a vital role in maintaining pregnancy and facilitating fetal growth. Cells in this extraembryonic compartment match the chromosomal sex of the embryo itself. Sex differences have been observed in common gestational pathologies, highlighting the importance of maternal immune tolerance to the fetal compartment. Over the past decade, several studies examining placentas from term pregnancies have revealed widespread sex differences in hormone signaling, immune signaling, and metabolic functions. Given the rapid and dynamic development of the human placenta, sex differences that exist at term (37–42 weeks gestation) are unlikely to align precisely with those present at earlier stages when the fetal–maternal interface is being formed and the foundations of a healthy or diseased pregnancy are established. While fetal sex as a variable is often left unreported in studies performing transcriptomic profiling of the first-trimester human placenta, four recent studies have specifically examined fetal sex in early human placental development. In this review, we discuss the findings from these publications and consider the evidence for the genetic, hormonal, and immune mechanisms that are theorized to account for sex differences in early human placenta. We also highlight the cellular and molecular processes that are most likely to be impacted by fetal sex and the evolutionary pressures that may have given rise to these differences. With growing recognition of the fetal origins of health and disease, it is important to shed light on sex differences in early prenatal development, as these observations may unlock insight into the foundations of sex-biased pathologies that emerge later in life.

Placental sex differences exist from early prenatal development, and may help explain sex differences in pregnancy outcomes.

Transcriptome profiling of early to mid-gestation placenta reveals that immune signaling is a hub of early prenatal sex differences.

Differentially expressed genes between male and female placenta fall into the following functional associations: chromatin modification, transcription, splicing, translation, signal transduction, metabolic regulation, cell death and autophagy regulation, ubiquitination, cell adhesion and cell–cell interaction.

Placental sex differences likely reflect the interaction of cell-intrinsic chromosome complement with extrinsic endocrine signals from the fetal compartment that accompany gonadal differentiation.

Understanding the mechanisms behind sex differences in placental development and function will provide key insight into molecular targets that can be modulated to improve sex-biased obstetrical complications.

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.

Concordance of the risk of neonatal respiratory morbidity assessed by quantitative ultrasound lung texture analysis in fetuses of twin pregnancies

To evaluate the concordance of the risk of neonatal respiratory morbidity (NRM) assessed by quantitative ultrasound lung texture analysis (QuantusFLM) between twin fetuses of the same pregnancy. Prospective study conducted in twin pregnancies. Fetal ultrasound lung images were obtained at 26.0–38.6 weeks of gestation. Categorical (high or low) and continuous results of the risk of NRM were compared between twins. Fetal ultrasound lung images from 131 pairs (262 images) of twins were included. The images were classified into three gestational age ranges: Group 1 (26.0–29.6 weeks, 78 images, 39 pairs [29.8%]); Group 2 (30.0–33.6 weeks, 98 images, 49 pairs [37.4%]) and Group 3 (34.0–38.6 weeks, 86 images, 43 pairs [32.8%]). Concordance was good in Groups 1 and 3 and moderate in Group 2. In Groups 2 and 3 at least one fetus presented high-risk results in 26.5% and 11.6% of twin pairs, respectively. Only gestational age < 32 weeks, gestational diabetes mellitus, and spontaneous conception were associated with a high risk of NRM in Group 2. There was good concordance of the risk of NRM between twins < 30.0 weeks and > 34.0 weeks. From 30.0 to 33.6 weeks 26.5% of the twin pairs had discordant results, with moderate concordance of the risk of NRM.

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.

Risk factors for hospitalisation in Welsh infants with a congenital anomaly

OBJECTIVES

To investigate risk factor associated with hospitalisation of infants with a congenital anomaly in Wales, UK.

DESIGN

A population-based cohort study.

SETTING

Data from the Welsh Congenital Anomaly Register and Information Service linked to the Patient Episode Database for Wales and livebirths and deaths from the Office for National Statistics.

PATIENTS

All livebirths between 1999 and 2015 with a diagnosis of a congenital anomaly, which was defined as a structural, metabolic, endocrine or genetic defect, as well as rare diseases of hereditary origin.

MAIN OUTCOME MEASURES

Adjusted OR (aOR) associated with 1 or 2+ hospital admissions in infancy versus no admissions were estimated for sociodemographic, maternal and infant factors using multinomial logistic regression for the subgroups of all, isolated, multiple and cardiovascular anomalies.

RESULTS

25 523 infants affected by congenital anomalies experienced a total of 50 705 admissions in infancy. Risk factors for ≥2 admissions were younger maternal age ≤24 years (aOR: 1.17; 95% CI 1.06 to 1.30), maternal smoking (aOR: 1.20; 1.10 to 1.31), preterm birth (aOR: 2.52; 2.25 to 2.83) and moderately severe congenital heart defects (aOR: 6.25; 4.47 to 8.74). Girls had an overall decreased risk of 2+ admissions (aOR: 0.84; 0.78 to 0.91). Preterm birth was a significant risk factor for admissions in all anomaly subgroups but the effect of the other characteristics varied according to anomaly subgroup.

CONCLUSIONS

Over two-thirds of infants with an anomaly are admitted to hospital during infancy. Our findings identified sociodemographic and clinical characteristics contributing to an increased risk of hospitalisation of infants with congenital anomalies.

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.

Examining Sex Differences in the Human Placental Transcriptome During the First Fetal Androgen Peak

Sex differences in human placenta exist from early pregnancy to term, however, it is unclear whether these differences are driven solely by sex chromosome complement or are subject to differential sex hormonal regulation. Here, we survey the human chorionic villus (CV) transcriptome for sex-linked signatures from 11 to 16 gestational weeks, corresponding to the first window of increasing testis-derived androgen production in male fetuses. Illumina HiSeq RNA sequencing was performed on Lexogen Quantseq 3' libraries derived from CV biopsies (n = 11 females, n = 12 males). Differential expression (DE) was performed to identify sex-linked transcriptional signatures, followed by chromosome mapping, pathway analysis, predicted protein interaction, and post-hoc linear regressions to identify transcripts that trend over time. We observe 322 transcripts DE between male and female CV from 11 to 16 weeks, with 22 transcripts logFC > 1. Contrary to our predictions, the difference between male and female expression of DE autosomal genes was more pronounced at the earlier gestational ages. In females, we found selective upregulation of extracellular matrix components, along with a number of X-linked genes. In males, DE transcripts centered on chromosome 19, with mitochondrial, immune, and pregnancy maintenance-related transcripts upregulated. Among the highest differentially expressed autosomal genes were CCRL2, LGALS13, and LGALS14, which are known to regulate immune cell interactions. Our results provide insight into sex-linked gene expression in late first and early second trimester developing human placenta and lay the groundwork to understand the mechanistic origins of sex differences in prenatal development.

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.

Temporal trends in diagnoses of congenital microcephaly, Texas Hospital Discharge Diagnoses, 2000-2015

OBJECTIVE

Assess temporal trends in congenital microcephaly.

METHODS

We used Texas inpatient discharge diagnoses between 2000 and 2015, restricting to newborns. Between 2000 and 2003, the maximum number of fields for recording diagnostic codes was eight, and between 2004 and 2015 it was 24. Microcephaly was classified into four subgroups based on co-occurring diagnoses: A (Known Causes), B (Other Birth Defects), C (Preterm Birth or Fetal Growth Restriction) and D (Isolated Cases).

RESULTS

We identified 2,301 cases of microcephaly or 4.0 cases per 10,000 live births. There was an increase in the prevalence of microcephaly in 2012-2015 compared with 2000-2003, odds ratio = 1.85 (95% CI 1.64-2.10) Significant temporal increases in microcephaly were observed within each of the four microcephaly subgroups and significant temporal increases were also observed for eight other neonatal diagnoses during the same time period. When we restricted our analysis to cases with microcephaly identified using only the eight diagnostic codes available throughout the entire study period, the temporal trend for microcephaly was diminished or absent.

CONCLUSIONS

It remains uncertain whether the observed increases in microcephaly and other neonatal diagnoses are real or an artifact of the change in the number of fields. However, since it is unlikely that there would be a simultaneous increase in microcephaly and eight other neonatal diagnoses, it is likely that some or all of the temporal increases in neonatal diagnoses are artifactual.

Sex Differences in Nutrition, Growth, and Metabolism in Preterm Infants

Biological differences between the sexes are apparent even from the early part of the pregnancy. The crown-rump length is larger in male fetuses compared to females in the first trimester. Placentae of male and female fetuses have different protein and gene expressions, especially in adverse conditions. Even within the intrauterine milieu, the same extracellular micro RNA may show upregulation in females and downregulation in male fetuses. There appears to be a natural survival advantage for females. Maternal glucocorticoids (GC) play an important role in fetal growth and organ maturation. However, excess glucocorticoids can not only affect growth but the response may be sex-specific and probably mediated through glucocorticoid receptors (GR) in the placenta. Mild pre-eclampsia and asthma are associated with normal growth pattern in males, but in female fetuses, they are associated with a slowing of growth rate without causing IUGR probably as an adaptive response for future adverse events. Thus, female fetuses survive while male fetuses exhibit IUGR, preterm delivery and even death in the face of another adverse event. It is thought that the maternal diet may not influence growth but may influence the programming for adult disease. There is growing evidence that maternal pre-pregnancy overweight or obesity status is directly associated with a higher risk of obesity in a male child, but not in a female child, at 1 year of age. It is observed that exposure to gestational diabetes is a risk factor for childhood overweight in boys but not in girls. It is fascinating that male and female fetuses respond differently to the same intrauterine environment, and this suggests a fundamental biological variation most likely at the cellular and molecular level.

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 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.

Birth weight discordance and adverse perinatal outcomes

OBJECTIVE

Our purpose was to examine the association between discordant growth and perinatal mortality and morbidity among twins with careful adjustment for maternal confounding factors.

STUDY DESIGN

Two cohorts with and without chorionicity data were compared using generalized estimating modeling.

RESULTS

Our population-based dataset consisted of 12,656 individual twins from whom 4% (452/12,656) had≥30% growth discordance. A subgroup of this population with chorionicity information had an incidence of 7.3%≥30% growth discordance. In growth-discordant twins, perinatal mortality and morbidity were higher than concordant pairs (P<0.01). Low Apgar score and perinatal mortality were more frequent in growth-discordant twins compared with growth-concordant ones (all P<0.01).

CONCLUSION

Birth weight discordance (BWD) places twins at increased risk of perinatal mortality. Growth discordance was also an independent risk factor for lower Apgar score of 5 min less than 5.

Climatic conditions and child height: Sex-specific vulnerability and the protective effects of sanitation and food markets in Nepal

Environmental conditions in early life are known to have impacts on later health outcomes, but causal mechanisms and potential remedies have been difficult to discern. This paper uses the Nepal Demographic and Health Surveys of 2006 and 2011, combined with earlier NASA satellite observations of variation in the Normalized Difference Vegetation Index (NDVI) at each child's location and time of birth to identify the trimesters of gestation and periods of infancy when climate variation is linked to attained height later in life. We find significant differences by sex: males are most affected by conditions in their second trimester of gestation, and females in the first three months after birth. Each 100-point difference in NDVI at those times is associated with a difference in height-for-age z-score (HAZ) measured at age 12-59 months of 0.088 for boys and 0.054 for girls, an effect size similar to that of moving within the distribution of household wealth by close to one quintile for boys and one decile for girls. The entire seasonal change in NDVI from peak to trough is approximately 200-300 points during the 2000-2011 study period, implying a seasonal effect on HAZ similar to one to three quintiles of household wealth. This effect is observed only in households without toilets; in households with toilets, there is no seasonal fluctuation, implying protection against climatic conditions that facilitate disease transmission. We also use data from the Nepal Living Standards Surveys on district-level agricultural production and marketing, and find a climate effect on child growth only in districts where households' food consumption derives primarily from their own production. Robustness tests find no evidence of selection effects, and placebo regression results reveal no significant artefactual correlations. The timing and sex-specificity of climatic effects are consistent with previous studies, while the protective effects of household sanitation and food markets are novel indications of mechanisms by which households can gain resilience against adverse climatic conditions.

A review of fundamental principles for animal models of DOHaD research: an Australian perspective

Epidemiology formed the basis of ‘the Barker hypothesis’, the concept of ‘developmental programming’ and today’s discipline of the Developmental Origins of Health and Disease (DOHaD). Animal experimentation provided proof of the underlying concepts, and continues to generate knowledge of underlying mechanisms. Interventions in humans, based on DOHaD principles, will be informed by experiments in animals. As knowledge in this discipline has accumulated, from studies of humans and other animals, the complexity of interactions between genome, environment and epigenetics, has been revealed. The vast nature of programming stimuli and breadth of effects is becoming known. As a result of our accumulating knowledge we now appreciate the impact of many variables that contribute to programmed outcomes. To guide further animal research in this field, the Australia and New Zealand DOHaD society (ANZ DOHaD) Animals Models of DOHaD Research Working Group convened at the 2nd Annual ANZ DOHaD Congress in Melbourne, Australia in April 2015. This review summarizes the contributions of animal research to the understanding of DOHaD, and makes recommendations for the design and conduct of animal experiments to maximize relevance, reproducibility and translation of knowledge into improving health and well-being.

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.

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.