Does the presence of a cesarean section scar influence the site of placental implantation and subsequent migration in future pregnancies: a prospective case-control study.

Abstract

To describe placental location in the first trimester of pregnancy and subsequent placental migration in women with and without a history of previous cesarean delivery. In this prospective case-control study, placental location was defined according to five anatomical sites in relation to the endometrial cavity. Placental localization was carried out by transabdominal ultrasound between 11 and 14 weeks' gestation. We recruited 738 women who had undergone one or more previous cesarean sections (CS) and 1856 patients without previous cesarean delivery. Comparative analysis was performed of placental location between the two groups, and to assess placental migration of those classified as being low lying at 20 and 32 weeks' gestation. There were significant differences in placental location between the two groups. In the CS group there were significantly more posterior and fewer fundal placentae than in the control group (47.2 vs 31.5% and 4.7 vs 15.5%, respectively). The number of previous cesarean deliveries did not have a significant effect on placental location. There was no significant difference in the incidence of anterior low-lying placenta between groups (1.5 vs 0.9%). Placental migration of the low-lying subtypes was similar in both groups (62 vs 64%). The presence of CS scars in the uterus are associated with an increase in the number of posterior placentae and a reduced number that implant in the fundus of the cavity. Migration of a low-lying placenta is independent of the presence of a CS scar in the uterus.