Periviable birth at 20 to 26 weeks of gestation: proximate causes, previous obstetric history and recurrence risk.

OBJECTIVE: Early preterm birth at 20 to 26 weeks of gestation (periviable birth) carries extreme risks of infant death and morbidities. Prevention of periviable birth could improve infant outcomes significantly. We sought to characterize the causes of periviable birth and to determine whether periviable birth can be predicted by previous pregnancy outcome.

STUDY DESIGN: We evaluated 104,921 pregnancies (1974-2004) and assessed the frequency and causes of periviable birth. Women who were delivered of both their first and second pregnancies at >20 weeks of gestation at our institution were identified. Predictive values of the first pregnancy outcomes for second pregnancy outcomes were determined.

RESULTS: Periviable birth complicated 1981 deliveries (1.9%). Seventy-nine percent of the women with periviable births had no history of periviable births; 44% of the women had no previous deliveries, and 35% of the women had previous term deliveries only. Causes of periviable birth were labor (36%), premature rupture of membranes (34%), bleeding (10%), and preeclampsia (4%). Four percent of the gestations were multiple gestations. Among 7970 pregnancies at >20 weeks of gestation, periviable birth in the first pregnancy was associated with preterm birth and periviable birth in the second pregnancy (35.6%, 6.9%; relative risk, 3.3 and 8.6; P < .0001). Periviable birth and preterm birth in the first pregnancy were insensitive for periviable birth in the second pregnancy (8.8%, 36.8%, respectively).

CONCLUSION: Although periviable birth is associated with subsequent periviable birth and preterm birth, preterm birth and periviable birth are insensitive markers for recurrences in the next pregnancy. Early pregnancy or preconceptional markers for prediction of periviable birth are needed.