Risk of preterm birth in a twin pregnancy after an early-term birth in the preceding singleton pregnancy: a retrospective cohort study

Objective To evaluate whether a history of spontaneous early-term birth (37(+0)-38(+6) weeks of gestation) in the previous singleton pregnancy is a risk factor for preterm birth (PTB) in a subsequent twin pregnancy. Design Retrospective cohort study. Settings Two French university hospitals (2006-2016). Population All women who delivered twins from 24(+0) weeks after a preceding singleton pregnancy birth at 37(+0) to 41(+6) weeks. Methods Multivariate logistic regression analysis of association between twin PTB and a previous spontaneous singleton early-term birth. Main outcome measures Twin PTB rate before 37, 34, and 32 weeks of gestation. Results Among 618 twin pregnancies, 270 were born preterm, 92 of them with a preceding spontaneous singleton early-term birth. The univariate analysis showed a significantly higher risk of twin PTB before 37, 34, and 32 weeks among those 92 women compared with those with a full- or late-term birth in their previous singleton pregnancy. This association remained significant after logistic regression (odds ratio [OR] between 2.42 and 3.88). The secondary analysis, restricted to the twin pregnancies with spontaneous PTB found similar results, with a risk of PTB before 37, 34, and 32 weeks significantly higher among women with a previous spontaneous singleton early-term birth, including after logistic regression analysis (OR between 3.51 and 3.56). Conclusion A preceding spontaneous singleton early-term birth is a strong and easily identified risk factor for PTB in twin pregnancies. Tweetable abstract Spontaneous 'early-term' birth of a singleton is a significant risk factor for future preterm births in twin pregnancies.