[Prophylactic cerclage in placenta praevia?]

In 12 patients a placenta previa was diagnosed sonographically between 17th and 24th gestational week. A prophylactic cerclage was done in all of them between 18th and 24th week. In no case a placenta previa could be proved by ultrasonic controls. Because of the so called migration of the placenta prophylactic measurements are indicated only after the 30th gestational week. A persistent pathological insertion has to be taken into account only at this moment.