Twin entanglement revisited.

A fear of interlocking twins is one factor that has led to a high Cesarean section (C/S) rate in breech (A)/vertex (B) (Br(a)/Vtx(b)) twins. We sought to estimate the frequency of occurrence of twin entanglement, and of interlocking Br(a)/Vtx(b) twins in vaginal deliveries. 541 twins and 48,195 deliveries were retrospectively studied for the period 1987-1995. The incidence of Br(a)/Vtx(b) deliveries was noted, and the number of deliveries marked by interlocking and collision of fetuses. The mode of delivery, reason for C/S, and sources of perinatal mortality were noted. Only 43 deliveries were Br(a)/Vtx(b) (7.9% of all twins) and of these only 14 (32.6%) were delivered vaginally. One case of interlocking (2.3% of all Br(a)/Vtx(b) pairs) and five cases of collision of twins (ie competition for entry into the pelvic inlet with obstruction) were noted. All cases mentioned were delivered by C/S. No perinatal mortality resulted from these cases. In recent years the trend has been for greater use of C/S and ultrasound in managing twin deliveries. In this study 67.4% of Br(a)/Vtx(b) twins were delivered by C/S. Although there are fewer vaginal deliveries of these twins and the rate for interlocking (2.3%; 95% CI: 0.06-12.3%) for the whole group has remained about the same, we found the rate in those twins allowed vaginal delivery was 6.7% (95% CI: 0.2-31.9%). The presentation at greatest risk for entanglement was found to be Br(a)/Vtx(b).