Introduction: The presence of a lowlying in the second trimester of pregnancy can be converted to an upper uterine segment placenta by the end of the third trimester. This phenomenon is important when a complete or marginal placenta previa is encountered in the second trimester of gestation because of the need to predict possible antepartum complications and mode of delivery. Aim: To examine the migration of placenta and the placental marginal sinus to predict the eventual route of delivery in low-lying placenta. Methodology: Women with a low-lying placenta with 30 weeks of gestation were included for study. The distance between the internal os and leading edge of the placenta was measured fortnightly using transvaginal ultrasonography until 36 weeks gestation. The relationship between the rate of placental migration, the presence of a placental marginal sinus and the eventual mode of delivery was investigated. Results: In the present study cesarean section rate was 60 % (39/65) in the slow migration group (0 – 2.0 mm/week) group, six patients (6/35) in the fast (more than 2.0 mm/week) migration group underwent a cesarean section (p < 0.01) because of other problems. The cesarean section rate was 75.9 % (22/29) in patients with a placental marginal sinus, significantly greater than the rate of 11.3 % (8/71) in patients without a marginal sinus (p < 0.01). Conclusion: A decreased rate of placental migration until 36 weeksÂ’ gestation and the presence of a placental marginal sinus were associated with subsequent cesarean delivery because of antepartum vaginal hemorrhage. These parameters may be useful for predicting the route of delivery in women with a lowlying placenta.