Association of external cephalic version before term with late preterm birth

INTRODUCTION: While evidence suggests that beginning an external cephalic version (ECV) before term (34^0/7 to 36^6/7 weeks) compared with after term may be associated with an increase in late preterm birth (34^0/7 to 36^6/7 weeks), it remains unknown what might account for this risk. The objective of the present study is to further investigate the association between ECV before term and late preterm birth. MATERIAL AND METHODS: Secondary analysis of data collected from the international, multicenter Early ECV trials. We evaluated the relation between ECV exposure and late preterm birth (34^0/7 to 36^6/7 weeks), as well as whether additional risk factors for preterm birth (such as maternal age, height, body mass index, parity, placental location, and perinatal mortality rate) moderated this relation. Generalized linear mixed methods were used to account for center effect and adjust for covariates. RESULT: Among 1765 women with breech pregnancies and without a prior preterm birth, 749 (42.4%) received at least one ECV before term. Exposure to an ECV before term was not associated significantly independently with odds of preterm birth. However, placenta location moderated the association between early ECV exposure and late preterm birth. The odds of preterm birth in women who were exposed to an ECV before term and who also had an anterior placenta were doubled (OR 2.05; 95% CI 1.12-3.71; p = 0.02). CONCLUSION: In a large cohort of women without known risks for preterm birth, those with an anterior placenta who undergo an ECV before term constitute a subgroup at particular risk for late preterm birth.