Prior Term Birth Decreases the Risk of Preterm Birth in a Subsequent Twin Gestation

The aim of the study is to examine the association between the risk of preterm delivery among women with twin pregnancies and their obstetric history.

We designed a retrospective cohort study of live twin births in 2008 in the United States that delivered after 24^0/7 weeks. Women were categorized into nulliparas, multiparas with prior term delivery, and multiparas with prior preterm delivery. The incidence of preterm birth was compared using Chi-square test and multivariable logistic regression models.

A total of 32,895 nulliparous and 64,701 multiparous women with twin pregnancies were included in the study. Of the multiparous women, 2,505 (4%) had a history of a prior preterm delivery. Multiparous women with prior term birth were more likely to deliver at term (: 43%): in the index twin pregnancy than nulliparous women (40%) and multiparous women with a prior preterm birth (21%; p < 0.001). Compared with nulliparous women, prior term birth was protective against preterm delivery (adjusted odds ratio [aOR] = 0.67 [95% confidence interval: 0.60-0.74] for delivery <28 weeks and aOR = 0.79 [0.71-0.77] for delivery <34 weeks).

Among multiparous women with twins, a prior term delivery appeared to be protective against preterm delivery compared with nulliparous women with twins.

· Prior term birth is protective against preterm birth in subsequent twin pregnancy.. · A prior term birth confers an OR of 0.66 for delivery prior to 28 weeks in twin pregnancies.. · A prior preterm birth renders a twin pregnancy nearly twice as likely to deliver before 28 weeks..