The implication of a low implantation of the placenta detected by ultrasonography in early pregnancy.

Ultrasonic scanning in the first and early in the second trimester of pregnancy showed a high incidence (18 per cent) of possible placenta previa. A placenta which reached onto the internal cervical os but did not cover it in early pregnancy was found to be in the upper segment at a repeat scanning in the third trimester. The placenta which covered the internal cervical os either partially or completely was associated with a higher incidence of bleeding, abortion and placenta previa which was confirmed at repeated ultrasonic examination and at delivery.