Ultrasound placental localisation in early pregnancy.

A retrospective study of 400 consecutive case records was made to establish the clinical significance of the low lying placenta found on ultrasound. Diagnostic accuracy is discussed. 30% of the patients had a low lying placenta on early scan. Of these, 73% had a follow up scan. There was a progressive drop in the incidence of low lying placentae through pregnancy until at term, in this study, there was no placenta previa. It is considered that a repeat scan is necessary to exclude placenta previa, but not until 34 weeks gestation. Amongst the patients with early low lying placentae the incidence of antepartum haemorrhage of indeterminate type was significantly high (P less than 0.001). A careful surveillance of these patients is therefore required. Dynamic placental migration may be the cause of this bleeding. Further study is necessary to determine the effect of early placental position on subsequent fetal development.