Fetal sex pairing and adverse perinatal outcomes in twin gestations

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

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).

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).

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.