Prediction of spontaneous preterm birth

Obstetric history

There is particular difficulty identifying at-risk women in their first pregnancy; among singletons, a history of sPTB remains the most powerful predictor. Twin pregnancies will be at 40% risk of delivering spontaneously before 37 weeks. A meta-analysis quantifying the risk of recurrence of sPTB based on different subtypes of subsequent pregnancy is summarized in Table 30.1. Women with a previous PTB at less than 37 weeks of gestation are at a significant increased risk for recurrent PTB compared with women who have a previous term birth (odds ratio (OR) 5.43; 95% confidence interval (CI) 4.03­7.31), with an increasing risk of subsequent PTB with decreasing gestational age in the previous pregnancy (7).