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

ABSTRACT

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.