Changes of placental site diagnosed by repeated ultrasonic examination

Over a period of two years, 7 137 localisations of placenta were performed. In 67 patients on the first examination it was found that the lower margin of placenta reached the internal os of the uterus. All these patients were followed up by examinations every two or four weeks. In 63 of the 67 patients, placental migration was found involving a change in the level of the lower placental edge from the cervix towards the fundus. The change in this position varied from 3 to 9 cm. All four cases where the placenta extended from anterior to posterior wall ended as placenta praevia. Ultrasonic proof of placental migration shows the necessity for ultrasonic examination shortly before the birth, as only then is the final diagnosis of placenta praevia possible.