Objectives This study aims to assess if three dimensional power Doppler (3DPD) ultrasound of the placenta, evaluating placental volume, vascularisation, and blood flow in post-term pregnancies differs from normal. It also examines whether computer analysis identifies the increased calcification normally present in the placenta after 40 weeks.

Methods This was a prospective cohort study involving 50 women with post-term pregnancies. Gestational age (GA) ranged from 40–41+6 weeks gestation. 3DPD ultrasound was used to evaluate placental volume, vascularisation index (VI), flow index (FI) and vascularisation-flow index (VFI). Following each scan the percentage of calcification was also calculated, by computer analysis. Results were compared with previously determined normal values (36–40 weeks gestation) and correlated with Doppler values and placental histology.

Results Results showed that placental volume, VI, FI and VFI are not influenced by GA when the pregnancy has advanced beyond 40 weeks and that values are similar between post-term pregnancies and normal pregnancies between 36 and 40 weeks. Placental volume was seen to decrease in post-term pregnancies as the mean UtA PI increased (P = 0.047). FI was reduced in cases where chorangiosis was found at histology (P = 0.033), identifying the increased vessel number associated with these cases. Computer analysis of placental calcification identified the increased calcification expected after 40 weeks, and also showed that calcification continues to increase between 40 and 42 weeks (P = 0.029).

Conclusion This study suggests that 3DPD placental assessment may provide additional information, assisting clinicians in decision making in post-term pregnancies.