Gender mix: does it modify birthweight--outcome association?

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.

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.

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.

Is there a relationship between fetal sex and placental pathological characteristics in twin gestations?

Background

Placenta plays a central role in mediating growth and development of fetuses. Sex-specific placentas may complicate this role.

Methods

The study aimed at investigating the association between fetal sex and placental pathological findings in twin gestations using generalized estimating equation modeling. We used a large population-based clinical data born in British Columbia (BC) and linked the fetal-maternal data to hand-searched pathology reports of 1493 twin placentas from twins born in BC Women hospital. We analyzed the data using generalized estimating equations taking the cluster nature of twins into consideration.

Results

About 26.5% of twins were monochorionic and 73.5% were dizygotic. Most twins were male (51.3%). About 2/3 of twins were sex concordant (66.6%). Of the sex concordant twins, similar percentages were male-male (34.7%) and female-female (31.2%). Of the sex discordant twins, the male-female (33.3%) group constituted about 1/3 of the whole population.

Adjusted for chorionicity, birth weight discordance ≥30% and gestational age, the odds of chorionitis (1.38, 95% CI = 1.04–1.84), anastomosis (1.63, 95% CI = 1.22–2.19), unequal sharing of placenta (1.72, 95% CI = 1.11–2.64), placental inflammation (1.30, 95% CI = 1.05–1.62) and lesions (1.83, 95% CI = 1.02–3.31) were higher in male twins compared with females. Twins of either sex from sex-discordant pairs were less likely to have placental anastomosis compared to the reference category. Males from male-male pairs had higher odds of unequal placental sharing (74% higher) and composite inflammation (52% higher) compared with the reference twins.

Conclusion

Our findings suggest a relationship between sex and placental pathological results.

[Life course genetic epidemiologic study based on longitudinal twin-family data: a new perspective]

Family-based life course epidemiology is the approach to clarify long-term effects of accumulations and chains of biological and social risk exposures in one's life trajectory, namely, before and during conception, infancy, childhood, young adulthood and later adult life. Both genetic and environmental factors are considered. One of the theoretical rationales is the 'developmental origin of health and disease (DOHaD)' hypothesis. According to this theory, the causes of adult diseases are attributed to predictive adaptive responses and biological programming or epigenetic changes during a critical period of early life. If the environment later in life after birth is different from what is predicted, a mismatch has happened, leading to the development of a disease. This theory is supported by many epidemiologic studies, animal experiments, and evolution theory of biology. Longitudinal twin-family data are very powerful and useful information in the family-based life course genetic epidemiologic study.

A study of the birth weight-obesity relation using a longitudinal cohort and sibling and twin pairs

Sibling and twin study designs provide control for confounding factors that are typically unmeasured in traditional cohort studies. Using nationally representative data from the National Longitudinal Study of Adolescent Health collected at 3 visits during 1994-2002, the authors evaluated the longitudinal association between birth weight and later obesity in a traditional cohort study (n = 13,763; ages 11-21 years at baseline), controlling for sex, age, race/ethnicity, and parental education. Among persons with a nonobese mother, high birth weight (>4 kg) participants were more likely than normal birth weight (>/=2.5-</=4 kg) participants to become obese later in life (incidence rate ratio = 1.46, 95% confidence interval: 1.28, 1.67). In a matched sibling pair sample (full siblings: n = 513; monozygotic twins: n = 207; dizygotic twins: n = 189), the authors examined longitudinal within-pair differences. Birth weight difference was positively associated with body mass index difference later in life for female monozygotic pairs only (beta = 2.67, 95% confidence interval: 0.99, 4.35). Given the null associations observed in the sibling sample, the commonly observed positive association between birth weight and later obesity from cohort analyses may be attributed to confounding by maternal characteristics. Further research is needed to identify specific factors that contribute to the birth weight-obesity relation.

Does fetal sex affect pregnancy outcome?

BACKGROUND

In maternal fetal medicine, gender differences in outcome are often observed.

OBJECTIVE

This article reviews the fetal sex-dependent differences found in many aspects of pregnancy, from conception through birth.

METHODS

The MEDLINE, EMBASE, and Current Contents databases were searched, for the years 1985 to 2006, using the following Medical Subject Headings and text words: fetal gender, finale, female, sex ratio at birth, pregnancy outcome, preterm birth, and stillbirth. The search was not limited by language. In addition, the bibliographies of known relevant articles were examined to capture any reports not already identified in the electronic search. All reports that provided information on gender differences in pregnancy outcome were included for review.

RESULTS

An extremely high male-to-female ratio was found in fetuses born after very short-duration pregnancy; this level declined around the 20th week and stabilized at term. In the absence of manipulation, both the sex ratio at birth and the population sex ratio have been found to remain consistent. A higher incidence of preterm birth and premature preterm rupture of membranes has been observed in different populations among mothers of male newborns compared with mothers of females. It has been speculated that this higher incidence may be linked to the relatively greater weight at lower gestational age of male newborns versus females. Women carrying male fetuses had higher rates of gestational diabetes mellitus, fetal macrosomia, failure to progress during the first and second stages of labor, cord prolapse, nuchal cord, and true umbilical cord knots. Cesarean sections were also more frequently found among male neonates compared with females.

CONCLUSIONS

Male sex is an independent risk factor for adverse pregnancy outcome. Evidence suggests that females have an advantage over males, with a better outcome in the perinatal period, particularly after preterm birth.

Can we generalise from findings in twins?

A number of recent studies have used data from twins to shed light on the causal pathways underlying the observed association between birthweight and cardiovascular risk factors or coronary heart disease. The issue of whether findings from twin studies are generally informative, or whether factors associated with twinning preclude generalisation, is considered here. It is concluded that the association between birthweight and later health may differ quantitatively between twins and singletons, but evidence regarding blood pressure suggests it may not differ qualitatively. However, more information is needed on a number of gestational and maternal factors, and on measures of health other than blood pressure. Placentation and issues relating to infertility and its treatment need to be recorded and, together with gestation length, may need to be taken into account in analyses.