Objective To evaluate not only the risk of total preterm birth (PTB) but also spontaneous preterm birth (sPTB) and indicated preterm birth (iPTB) in vanishing twin (VT). Study design This is a secondary analysis of a multicenter prospective cohort study. In 12 different healthcare institutions, women with singleton pregnancies were enrolled in early pregnancy and followed up till delivery. Results A total of 4,746 women were included in the final analysis, and.The frequency of VT was 1.1% (54/4746). VT group had a higher risk for total PTB (PTB<34 weeks, 2.1% vs. 14.8%, p<0.001; PTB<32 weeks, 1.6% vs. 13.0%, p<0.001; PTB<28 weeks, 0.9% vs. 13.0%, p<0.001) than singleton group. The VT group had increased risk for both sPTB and iPTB (<34 weeks, <32 weeks, and <28 weeks), and this increased risk for sPTB and iPTB in VT group remained significant even after controlling for confounders such as maternal age, parity, pre-pregnancy BMI, and mode of conception. Conclusion Vanishing twin can be an independent risk factor for both sPTB and iPTB when compared with singleton pregnancy.
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