Delayed interval delivery in twin pregnancies in the United States: Impact on perinatal mortality and morbidity

Objective To estimate the incidence of delayed interval delivery in twin pregnancies in the United States and evaluate the impact of delayed delivery on perinatal outcomes. Study design A population-based retrospective cohort study was performed using the U.S. “matched multiple birth” file (1995 to 1998), restricting our analysis to twin sets in which the first twin was delivered vaginally at 22 to 28 weeks (n = 4257). Outcomes examined included perinatal and infant mortality and small-for-gestational-age births. Outcomes of second twins in pregnancies that underwent delayed interval delivery of 1, 2, 3, and ≥4 weeks were compared with those in which both twins were delivered contemporaneously. Results In this cohort, 6.1% (n = 258) of twins had delayed delivery (≥1 week) of the second twin. Decreases in perinatal and infant mortality were observed only when the first twin was delivered at 22 to 23 weeks and when the delivery interval was ≤3weeks. However, for intervals ≥4 weeks or when the first twin was delivered at 24 to 28 weeks (regardless of delivery interval), there was no benefit in perinatal or infant mortality. Delayed delivery of ≥4 weeks was associated with increased risk of small-for-gestational-age birth in the second twin, regardless of gestational age at delivery of the first. Conclusion When a first twin was delivered at 22 to 23 weeks, delayed delivery of the second twin was associated with reduced perinatal and infant mortality of the second twin if the interval was less than 3 weeks. Delayed delivery of the second twin when the first was delivered at ≥24 weeks had no benefit on mortality.