Risk of preterm delivery and growth restriction in twins discordant for structural anomalies

We sought to determine whether twin gestations with an anomalous fetus are at increased risk of preterm delivery or intrauterine growth restriction (IUGR) compared to twins with 2 normal fetuses. This was a retrospective cohort of twins undergoing ultrasound 15-22 weeks' gestation. Groups were defined by the presence of 1 twin with a major anomaly (discordant) or by twins with no major anomalies (normal). The primary outcomes were preterm delivery (<37 weeks) and IUGR (<10th percentile). Of 1977 twin pregnancies, 66 had a twin with a major anomaly. Preterm delivery occurred in 42 (63.6%) discordant twins, compared to 1271 (66.5%) normal twins (risk ratio, 1.0; 95% confidence interval, 0.81.2). IUGR was diagnosed in 15 (22.7%) normal co-twins, compared to 406 (21.3%) presenting twins in normal twins (risk ratio, 1.1; 95% confidence interval, 0.71.7). Twins discordant for major anomalies are not at increased risk of preterm delivery or IUGR compared to twins with no major anomalies.