Objective: Most studies determining risk of preterm birth in a twin pregnancy subsequent to a previous preterm birth are based on linkage studies or small sample size. We wished to identify recurrent risk factors in a cohort of mothers with a twin pregnancy, eliminating all known confounders. Methods: We conducted a retrospective cohort study of twin births at a tertiary care centre in Montreal, Quebec, between 1994 and 2008, extracting information, including chorionicity, from patient charts.To avoid the effect of confounding factors, we included only women with a preceding singleton pregnancy and excluded twin-to-twin transfusion syndrome, fetal chromosomal/structural anomalies, fetal demise, and preterm iatrogenic delivery for reasons not encountered in both pregnancies. We used multiple regression and sensitivity analyses to determine recurrent risk factors. Results: Of 1474 twin pregnancies, 576 met the inclusion criteria. Of these, 309 (53.6%) delivered before 37 weeks. Preterm birth in twins was strongly associated with preterm birth of the preceding singleton (adjusted OR 3.23; 95% CI 1.75 to 5.98). The only other risk factors were monochorionic twins (adjusted OR 1.82; 95% CI 1.21 to 2.73) and oldest or youngest maternal ages. Chronic or gestational hypertension, preeclampsia, and insulin-dependent diabetes during the singleton pregnancy did not significantly affect risk. Conclusion: Preterm birth in a previous singleton pregnancy was confirmed as an independent risk factor for preterm birth in a subsequent twin pregnancy. This three-fold increase in risk remained stable regardless of year of birth, inclusion/exclusion of pregnancies following assisted reproduction, or defining preterm birth as < 34 or < 37 weeks' gestational age. Until the advent of optimal preventive strategies, close obstetric surveillance of twin pregnancies is warranted.
Michaluk, A., Dionne, M. D., Gazdovich, S., Buch, D., Ducruet, T., & Leduc, L. (2013). Predicting Preterm Birth in Twin Pregnancy: Was the Previous Birth Preterm? A Canadian Experience. Journal of Obstetrics and Gynaecology Canada, 35(9), 793–801. https://doi.org/10.1016/S1701-2163(15)30835-5