Placental microvascular changes in twin pregnancies with abnormal umbilical artery waveforms

Objective: To determine whether there is a relationship between umbilical artery Doppler waveforms and placental histology in twin pregnancies. Methods: The placental vasculature was examined histologically in 41 cases of twin pregnancy in women who had undergone antenatal Doppler umbilical artery waveform analysis. Results: Those fetuses with abnormal systolic-diastolic ratios (S/Ds) showed a reduction in the placental tertiary stem villi arterial vessels compared with fetuses with normal S/Ds. The mean count of small arterial vessels (diameter less than 90 μ.) in the placentas from cases with normal S/Ds (below the 95th percentile) was 5.6, whereas the mean arterial count for those with high S/Ds (above the 99th percentile) was 3.9 (P =.039). Conclusions: In twin pregnancies complicated by placental insufficiency, there is microvascular disease restricted to the placenta of the affected fetus. This suggests that the placental vascular lesion originates in the fetal circulation rather than in the uteroplacental vasculature.