Association of Resolved Low-Lying Placentation With Risk of Postpartum Hemorrhage

To evaluate whether individuals who have a placenta previa or low-lying placenta that resolves before delivery are at increased risk of postpartum hemorrhage and postpartum hemorrhage-related morbidity.

This was a prospective, multicenter, 1:3 matched cohort study of pregnant individuals with singleton gestations diagnosed with low placentation by transvaginal scan at 19 to 23 weeks of gestation between January 2021 and December 2023 at nine academic maternity centers (exposed participants). Unexposed participants were those with a normally located placenta, matched in a 1:3 ratio according to parity. Resolution of low placentation was diagnosed when placenta was at 20 mm or more from the internal os. Individuals with fetal anomalies, hematologic disorders, therapeutic anticoagulation, placenta accreta spectrum disorder, vasa previa, persistent low placentation at birth, and delivery at a nonenrolling center were excluded. Primary outcome was postpartum hemorrhage of 1,000 mL or more. Secondary outcomes included postpartum hemorrhage of 1,500 mL or more, use of second-line uterotonic drugs, blood transfusions, additional procedures to control bleeding, intensive care unit admission, and hospital stay for more than 7 days. Multivariable logistic regression adjusted for confounders was used to estimate independent associations with outcomes.

The study population included 182 exposed and 589 unexposed participants. Individuals with resolved low placentation had higher rates of smoking (P=.024), prior dilation and curettage (P=.012), posterior placenta (P<.001), and induction of labor (P=.038). Multivariate logistic regression analysis adjusted for confounders showed that exposed people had higher odds of postpartum hemorrhage of 1,000 mL or more (13.2% vs 4.1%, adjusted odds ratio [aOR] 3.1) compared with unexposed people and of use of second-line uterotonic drugs (28.0% vs 12.4%, aOR 2.69) and tranexamic acid (16.5% vs 7.5%, aOR 2.19), as well as hospital stay longer than 7 days (11.5% vs 3.4%, aOR 2.63).

Individuals with resolved low placentation are at increased risk of postpartum hemorrhage and related complications compared with those who always had a normally located placenta.