[Ultrasonographic assessment of changes in the location of the lower border (termed migration) of the placenta].

Ultrasonographic assessment of the so called placental migration was done in 136 patients in whom the preliminary diagnosis was made between 18th and 34th week of pregnancy. It was found that placental migration was a commonly observed phenomenon in patients with preliminary diagnosis of low-located marginal placenta previa while in the case of central placenta previa it occurred sporadically only in the second trimester of pregnancy. The lower placental border migration rate was higher in the second than in the third trimester of pregnancy.