The Likelihood of Change in Fetal Presentation During the Third Trimester in Twin Pregnancies

To estimate the likelihood and identify predictors of spontaneous fetal version during the third trimester in twins using data from a multicenter randomized controlled trial on mode of delivery in twin pregnancies.

Women with twin pregnancies after 32 weeks of gestation in which twin A was vertex were randomized to planned cesarean or planned vaginal delivery. In the current study we analyzed the likelihood of a spontaneous version of any of the twins between ultrasound assessment at the time of randomization and delivery.

A total of 2,603 women were analyzed. Twin A tended to persist in the vertex presentation after 32 weeks of gestation with a spontaneous version rate to nonvertex presentation of 3.0% (95% confidence interval [CI] 2.3-3.7%). Twin B was less stable and underwent spontaneous version in 24.8% (95% CI 23.1-26.5%) of cases; the rate remained higher than 20% even after 34 weeks of gestation. On multivariable analysis, twin A was more likely to undergo version when twin B was smaller (adjusted odds ratio [OR] 2.0, 95% CI 1.04-3.3), when twin B was breech (adjusted OR 3.7, 95% CI 2.2-6.4) or transverse (adjusted OR 2.9, 95% CI 1.6-5.5), and when the interval to delivery exceeded 4 weeks (adjusted OR 2.5, 95% CI 1.3-5.0). Twin B was more likely to undergo version when it was in the breech presentation (adjusted OR 1.7, 95% CI 1.4-2.1) or transverse lie (adjusted OR 3.1, 95% CI 2.5-3.9) compared with vertex presentation, when it was smaller (adjusted OR 1.7, 95% CI 1.1-2.0), when the interval to delivery exceeded 4 weeks (adjusted OR 1.7, 95% CI 1.3-2.4), and in multiparous women (adjusted OR 1.3, 95% CI 1.04-1.5).

The likelihood of spontaneous version of twin A after 32 weeks of gestation is low when twin A is in the vertex presentation but is much higher for twin B, even late during the third trimester.

ClinicalTrials.gov, www.clinicaltrials.gov, NCT00187369.

II.