Placental placement on the lower uterine segment without praevia: A postpartum hemorrhage risk?

Postpartum hemorrhage (PPH) is a leading cause of maternal death worldwide. We aimed to determine whether placement of a non-previa placenta on the lower uterine segment is associated with an increased risk of PPH.

This is a single-center observational study of pregnant women attending a third trimester screening ultrasound. As the distance from the internal cervical os to the lower edge of the placenta is not routinely measurable, we approximated it by systematic measurement between the postero-inferior point of the bladder and the lower edge of the placenta (PLA-B). Placentas lying on the lower uterine segment were defined as PLA-B <100 mm. The primary outcome was occurrence of moderate PPH (≥500 mL).

A total of 560 pregnant women were included in the study; 216 (38.6%) had placental placement on the lower segment (<100 mm), mostly distant from the internal cervical os: 129 between 80 and 99 mm (23.0%), 61 between 60 and 79 mm (10.9%), 18 between 40 and 59 mm (3.2%) and eight between 20 and 39 mm (1.4%). Eighty-five women had moderate PPH (15.2%) and 22 had severe PPH (≥1000 mL) or were transfused (3.9%). Lower segment placental placement (≥100 mm) was not associated with a significant increase in PPH risk, whether moderate (13.4% vs. 16.3%, OR = 0.80 [CI 95% 0.47-1.34]) or severe (2.3% vs. 4.9%, OR = 0.46 [CI 95% 0.14-1.35]). Within those with lower segment placement, there was no trend toward increased bleeding risk according to threshold (<40, <60, or <80 mm).

Placenta placement between 20 and 100 mm does not appear to increase PPH risk relative to placenta placement >100 mm.