The preterm prediction study: effect of gestational age and cause of preterm birth on subsequent obstetric outcome. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network.

OBJECTIVE: We sought to evaluate the association between prior spontaneous preterm delivery and subsequent pregnancy outcome. STUDY
DESIGN: A total of 1711 multiparous women with singleton gestations were prospectively evaluated at 23 to 24 weeks' gestation. Prior pregnancies were coded for the presence or absence of a prior spontaneous preterm delivery. If a prior spontaneous preterm delivery had occurred, the gestation of the earliest prior delivery (13-22, 23-27, 28-34, and 35-36 weeks' gestation) was recorded. Current gestations were categorized as spontaneous preterm delivery at <28, <30, <32, <35, or <37 weeks' gestation. The risk of spontaneous preterm delivery in the current gestation was determined on the basis of the occurrence, gestational age, and cause of the earliest prior spontaneous preterm delivery.
RESULTS: The incidences of spontaneous preterm delivery before 28, 30, 32, 35, and 37 weeks' gestation were 0.8%, 1.1%, 1.9%, 5.1%, and 11.9%, respectively. Those with a prior spontaneous preterm delivery carried a 2.5-fold increase in the risk of spontaneous preterm delivery in the current gestation over those with no prior spontaneous preterm delivery (21. 7% vs 8.8%; P </=.001). Gravid women with an early prior spontaneous preterm delivery (23-27 weeks' gestation) had a higher risk of recurrent spontaneous preterm delivery (27.1% vs 8.8%; P </=.001). Prior spontaneous preterm delivery was more closely associated with subsequent early spontaneous preterm delivery at <28 weeks' gestation (relative risk, 10.6) than for spontaneous preterm delivery overall (relative risk, 2.5). An early prior spontaneous preterm delivery (23-27 weeks' gestation) was most highly associated with early spontaneous preterm delivery (<28 weeks' gestation) in the current gestation (relative risk, 22.1). The relationship between prior spontaneous preterm delivery and current outcome was not as strong for those with a very early spontaneous preterm delivery (13-22 weeks' gestation). Prior spontaneous preterm delivery caused by preterm premature rupture of the membranes and preterm labor was significantly associated with similar outcomes in the current gestation (P <.001).
CONCLUSION: Prior spontaneous preterm delivery is highly associated with recurrence in the current gestation. An early prior spontaneous preterm delivery is more predictive of recurrence and is most highly associated with subsequent early spontaneous preterm delivery.