Sonographic assessment of placental migration in second trimester low lying placenta.

To assess the migration of low lying placenta diagnosed in the second trimester ultrasonogram (USG). All the women attending antenatal OPD clinic had undergone routine obstetric USG in the second trimester (14 weeks onwards). Those cases who had low lying placenta lower edge of placenta within 3.0 cms from the cervical internal os were included in the study. These cases were subjected to be followed up at 4 weekly interval to repeated serial ultrasonogram by Transabdominal and/or Transvaginal USG well through 3rd trimester of pregnancy or delivery which ever was earlier. Of the total 1229 second trimester USG, 312 (25.3%) women had low lying placenta in the second trimester. Follow up of this 312 cases indicated that in 288 (92.4%) cases it had migrated to upper segment by 3rd trimester. The migration of placenta was 92.4% and 68.0 % where the distance between the leading edge of placenta and cervical internal os was more than 2.0 cm or less than 2 cm respectively. Migration was not observed in women where the distance was less than 1.5 cm. Placental migration was 94.5% in anteriorly situated placenta and 90.2% in posteriorly situated placenta. The rate of placental migration was 95.1%, 77.7%, 55.5% in women who had previous normal delivery, previous caesarean delivery and prior history of dilatation and curettage (D & C) or manual removal of placenta (MRP), respectively. The prevalence of low lying placenta in 2nd trimester is 25.3%, which reduces to 7.3% at term. The rate of placental migration was over 90.0%. Factor like initial distance between the lower edge of the placental and cervical internal os. placental position and previous birth by caesarean section influence the placental migration.