Placental volume measurement by ultrasonography: evaluation of the method.

A method for placental volume measurement by parallel ultrasonographic section scans is presented. An interval of 2 cm between the scans proves most effective. During measurement the patient should lie in the lateral position to prevent caval vein compression. The precision of the method as estimated by the SE is between 10 and 50 ml. The volume measured reflects both placental cellular mass and placental circulating blood volume. Drainage of the latter after delivery causes a fairly large difference between antepartum placental volume and postpartum placental weight (volume/weight ratio 1:6).