Difference in migration of placenta according to the location and type of placenta previa

To correlate the incidence and rate of placental migration with the mode of delivery, pregnancy outcome, and maternal complication according to the location (anterior versus posterior) and type of placenta previa (PP).

We prospectively evaluated the placentas of 98 pregnant women with PP or low-lying placenta (LLP) at the prenatal sonographic examination performed between 20 and 27 gestational weeks. We divided the pregnant women into groups according to type and location of PP. Follow-up sonographic examination was performed between 32 and 37 weeks. We compared incidence of migration to the normal position and calculated the migration rate as the migrated distance divided by the weeks of interval between 2 sonographic examinations. We compared the incidences of cesarean section, fetal outcome, and maternal complications during the pregnancy.

The incidence of migration in the group of anterior placentas was significantly higher than that in the group of posterior placentas. The mean migration rate in the anterior group was 2.6 mm/week, whereas that in the posterior group was 1.6 mm/week. The migration rate of incomplete PP was significantly higher than that of LLP. Incidence of cesarean section for nonmigrated PP was significantly higher in the posterior group. The incidences of premature delivery and vaginal spotting were also significantly higher in the posterior group.

Anterior PP and LLP may migrate more often and faster than posterior PP. Our results may be useful for planning of prenatal management and counseling patients with PP and LLP.