852: What is the likelihood of spontaneous change of fetal presentation following 3rd trimester ultrasound in twin pregnancies?

To determine the likelihood of spontaneous change of fetal presentation following 3rd trimester ultrasound in twin pregnancies, and to identify factors that affect the likelihood of spontaneous fetal version. This was a secondary analysis of the data of the “Twin Birth Study” in which women presenting with twin pregnancies after 32 weeks of gestation with the first twin in vertex presentation were randomized to planned cesarean section or planned vaginal delivery. In the current study we analyzed the likelihood of a spontaneous change in twins presentation between initial enrollment and delivery. A total of 2612 women with twin pregnancies were included in the analysis. The overall likelihood of change of presentation for twin A was 3.1% and was related to the enrollment-to-delivery interval (Figure). The overall likelihood of change of presentation for twin B was 24.8% and was also related to the enrollment-to-delivery interval (p<0.001) as well as to gestational age at enrollment (Figure). A vertex presentation of twin B and a higher estimated weight of twin B at the time of enrollment were associated with the lowest likelihood of change in presentation for twin A (1.7% and 1.9%, respectively) and twin B (18.0% and 20.5%, respectively). Nulliparity was associated with a lower risk of change in presentation for twin B (21.5% vs. 27.0%, p=0.002) but not for twin A (3.0% vs. 3.2%, p=0.7). The likelihood of change in presentation after 32 weeks is relatively low when twin A is in vertex presentation,although this small risk persists even after 36 weeks. The risk is substantially higher for twin B. This information can be used to determine the need for repeat sonographic assessment during the 3rd trimester, especially in settings in which the presentation of twin B affects the decision regarding mode of delivery due to limited experience in maneuvers such as fetal breech extraction.