EXTERNAL CEPHALIC VERSION BEFORE TERM AND THE RISK OF PRETERM BIRTH

Abstract

Background: External cephalic version (ECV) is an obstetric maneuver used to turn a fetus from breech (buttocks first) to cephalic (head first) presentation. A Cochrane Review suggests that beginning ECV earlier in pregnancy (before 37 weeks) compared to later in pregnancy (37 weeks onwards) is associated with a decreased likelihood of breech presentation and cesarean section; however, it appears to be associated with an increase in late preterm birth (PTB; <37 weeks).

Objective: To explore the association between early ECV and the risk of PTB.

Method: Secondary data analyses of the Early ECV Trials. 1765 women with low-risk breech pregnancies were enrolled with 749 receiving at least one ECV before term. Accounting for centre in our analyses, risk factors for PTB, including exposure to early ECV, were analyzed for their contribution to odds of PTB. Interactions between risk factors and early ECV were explored. Characteristics among women who received an ECV before term and delivered PTB (N=48) were described.

Results: Early ECV exposure was not an independent predictor of PTB; however, the interaction between early ECV and anterior placental location was a significant predictor, and associated with a two-fold increase in the odds of PTB (OR: 2.05; 95% CI: 1.12 – 3.71; p=.02). Compared to other women in the study, women with an ECV before term who delivered PTB (N=48) were more likely to have an anterior placenta (67% vs. 35%), and this proportion was even higher among women who delivered preterm and within 48 hours of early ECV exposure (75%).

Conclusion: Exposure to early ECV was associated with risk of PTB for women with an anterior placenta. The manipulation that occurs during an ECV may induce fetal distress in a preterm fetus and/or increase risk of uteroplacental hemorrhage for those with an anterior placenta. These biological pathways may be triggered and initiate PTB.