Placental volume in twin and triplet pregnancies measured by three-dimensional ultrasound at 11 + 0 to 13 + 6 weeks of gestation.

OBJECTIVE To compare the placental volume at 11 + 0 to 13 + 6 weeks' gestation between singleton and multiple pregnancies and to examine the possible effect of chorionicity on placental volume. METHODS The placental volume was measured by three-dimensional (3D) ultrasound using the Virtual Organ Computer-aided AnaLysis (VOCAL) technique in 290 consecutive twin and 37 triplet pregnancies at 11 + 0 to 13 + 6 weeks of gestation. For the comparison of twin, triplet and singleton placental volumes each measurement was expressed as a multiple of the median (MoM) for singletons, previously established from the study of 417 normal fetuses at 11 + 0 to 13 + 6 weeks of gestation. RESULTS Median twin and triplet placental volumes were 1.66 and 2.28 MoM for singletons, respectively. In twins the placental volumes increased significantly with gestation from a median of 83.6 mL (5th and 95th centiles: 56.0 mL and 124.9 mL) at 11 + 0 weeks to 149.3 mL (5th and 95th centiles: 100.0 mL and 223.1 mL) at 13 + 6 weeks. The median MoM in monochorionic twins was not significantly different from that in dichorionic twins with fused placentas or dichorionic twins with separate placentas. In triplets the placental volumes increased significantly with gestation from a median of 114.9 mL (5th and 95th centiles: 77.6 mL and 170.1 mL) at 11 weeks to 217.9 mL (5th and 95th centiles: 147.2 mL and 322.5 mL) at 13 + 6 weeks. There were no significant differences in total placental volume between monochorionic and dichorionic triplets, monochorionic and trichorionic triplets, or dichorionic and trichorionic triplets. CONCLUSIONS Placental volume in multiple pregnancies does not depend on chorionicity, and the rate of placental growth between 11 and 13 + 6 weeks is not significantly different between singletons, twins and triplets. Moreover, for a given gestational age the placental volume corresponding to each fetus in twins and triplets is 83% and 76%, respectively, of the placental volume in singletons.