Significance of growth discordance in appropriately grown twins.

Objective: We sought to determine the perinatal risks associated with growth discordance in appropriately grown twin gestations.

Methods: We conducted a retrospective cohort study of all twin gestations excluding those complicated by monoamnionicity, twin-twin transfusion syndrome, structural anomalies, selective reduction, or a birthweight <10th percentile. Growth discordance was defined as ≥20%. Outcomes considered were stillbirth, preterm delivery <34 weeks and <28 weeks, and admission to the neonatal intensive care unit. Analyses were stratified by chorionicity.

Results: Of 895 included dichorionic pregnancies, 63 (7.0%) were discordant. Discordant dichorionic twins were not at increased risk of preterm delivery <34 weeks (34.9% vs 25.6%; relative risk [RR], 1.4; 95% confidence interval [CI], 1.0-1.9), preterm delivery <28 weeks (3.2% vs 2.8%; RR, 1.1; 95% CI, 0.3-4.8), or admission to intensive care (26.9% vs 23.5%; RR, 1.5; 95% CI, 1.0-2.3). We had >90% power to detect a 2.5-fold increase in preterm delivery and admission to the neonatal intensive care unit in dichorionic twins. Of 250 monochorionic pregnancies, 23 (9.2%) were discordant. Monochorionic twin pregnancies were at increased risk of preterm delivery <34 weeks (65.2% vs 26.4%; RR, 2.5; 95% CI, 1.7-3.6), preterm delivery <28 weeks (34.8% vs 4.0%; RR, 8.8; 95% CI, 3.7-20.5), and admission to intensive care (68.2% vs 23.3%; RR, 2.9; 95% CI, 2.0-4.3).

Conclusions: In appropriately grown twins, growth discordance is a risk factor for adverse perinatal outcomes in monochorionic, but not dichorionic, twins. Discordant monochorionic twins may benefit from increased antenatal surveillance.