Variations of placental migration in patients with early third trimester malposition

This study aimed to investigate the impact of placental migration on the definitive prepartum diagnosis of patients with placenta previa (PP) and low-lying placenta (LLP) after late preterm.

This was a retrospective cohort study of singleton pregnancies with PP and LLP diagnosed at 30-33 weeks of gestation. We assessed the rate of changes in transvaginal ultrasonographic measurements of placental position during the period from 34 to 38 weeks of gestation.

A total of 127 cases (82 of PP, 45 of LLP) were included. The PP group comprised 34 cases with complete PP and 48 with partial and marginal PP. The diagnosis of complete PP was changed to partial or marginal PP in two (5.9%) cases. Concerning cases with partial and marginal PP, 14 (29.2%) were eventually revised to LLP and four (8.3%) ultimately normalized. Among the patients with LLP, placental position was normalized in 23 (51.1%). Overall, a revision in diagnosis after late preterm was required in 48 cases (37.8%). Among the 93 patients who did not have complete PP, 46 (49.5%) needed revisions of their placental diagnosis.

Repeated evaluations of placental position by ultrasonography after late preterm could be of significant value in selecting the most appropriate mode of delivery.