[The clinical history of midtrimester low placentation].

The finding of low implantation of placenta during midtrimester is not uncommon. It does not constitute an immediate obstetric emergency, but rather demanding serial and thorough follow-up. Previous uterine trauma and scarring caused by Caesarean section is a significant predisposing factor, while the roles of maternal age, gravidity, parity, sex of newborn are controversial. Placenta previa patients have a tendency to develop antepartum hemorrhage and preterm labor. Neither IUGR nor congenital malformations are associated abnormalities in our study. The rate of cesarean section in patients with placenta previa has increased, but the risk of perinatal morbidity has not increased. "Migration" means the dynamic relationship between the placenta and internal O.S., which occurred in 79.6% cases overall, especially in the subgroup of low-lying and marginal placenta previa. The "migration" does not protect patients from operation, nonetheless, the defined "placenta previas" are not all destined to cesarean section. Ultrasonography is a helpful diagnostic tool, via abdominal or vaginal route, and is a practical guide of expectant management.