Association between the Degree of Twin Birthweight Discordance and Perinatal Outcomes

BACKGROUND:  Twin birthweight discordance is associated with adverse outcomes. OBJECTIVE:  To determine what degree of twin birthweight discordance is associated with adverse outcomes. STUDY DESIGN:  This is a retrospective cohort study of twins with vertex twin A delivered vaginally at 36 to 40 weeks (U.S. Vital Statistics Natality birth certificate registry data 2012-2014). The primary outcome was a composite of neonatal morbidity: 5-minute Apgar < 7, neonatal intensive care unit admission, neonatal mechanical ventilation > 6 hours, neonatal seizure, and/or neonatal transport to a higher level of care. Effect estimates were expressed as incidence rate and adjusted odds ratio (aOR) controlling for confounding using multivariate clustered analysis for between-pair effects, and multilevel random effect generalized estimating equation regressions to account for within-pair effects. We adjusted for sex discordance, breech delivery of the second twin, maternal race/ethnicity, nulliparity, age, marital status, obesity, and socioeconomic status. RESULTS:  In comparison to birthweight discordance of ≤20%, aORs with 95% confidence intervals (CIs) by weight discordance of the primary outcome among 27,276 twin deliveries were as follows: 20.01 to 25% (aOR: 1.46 [95% CI: 1.29-1.65]); 25.01 to 30% (aOR: 1.96 [95% CI: 1.68-2.29]); and 30.01 to 60% (aOR: 2.97 [95% CI: 2.52-3.50]). CONCLUSION:  Twin birthweight discordance >20% was associated with increased odds of adverse neonatal outcome.