Our objective was to determine the incidence and rate of persistence of placenta previa diagnosed at 15-20 weeks' gestation by using transvaginal sonography (TVS), and to describe the characteristics of TVS that predict placenta previa at delivery. Patients having placental tissue within 20 mm of the cervical os were prospectively identified by transabdominal ultrasound and underwent TVS. The distance of the placental edge from the cervical os was measured in millimeters. Characteristics of TVS predicting placenta previa at delivery were analyzed by logistic regression. The incidence of placenta previa diagnosed by TVS at 15-20 weeks was 1.1%; 14% persisted until delivery. Gestational age at the time of TVS and the distance of the placental edge to the cervical os helped predict placenta previa at delivery. Between 15 and 24 weeks' gestation, placenta overlapping the internal os by > or = 10 mm identified patients at risk of placenta previa at delivery with 100% sensitivity and 85% specificity. The use of TVS in the second trimester to diagnose placenta previa resulted in a lower incidence than was historically reported with the use of transabdominal ultrasound. The distance of the placental edge from the cervical os helps identify patients at risk of previa at delivery.

For patients with premature rupture of membranes, the gestational age at time of rupture carries the highest risk correlation with subsequent pulmonary hypoplasia.

The purpose of this study was to determine in what percentage of cases the assessment of placental localization using transabdominal sonography (TAS) was changed after transvaginal sonography (TVS) was applied. TVS was prospectively performed on all pregnant women of at least 15 weeks' gestation, when the placental edge using TAS appeared to be over or within 2 cm (low-lying) of the internal cervical os. The time required for the TVS scan and the distance of the placental edge from the internal cervical os were recorded. Of the 168 patients entered into the study, 131 were analyzed. Landmarks were poorly seen in 50% of the cases when using TAS. In 66 cases, the placenta appeared low or possibly over the internal cervical os using TAS, but a definitive diagnosis could not be made due to suboptimal visualization. In the remaining 65 cases, visualization of the internal os and placental edge was possible using both TAS and TVS. In this group, there was a change in the diagnosis in 26% of the cases after TVS was performed. Our results suggest that optimal visualization of the placental edge and internal cervical os is usually difficult with TAS when the placenta appears low-lying or over the internal cervical os. The assessment of placental localization was changed in over one-quarter of cases (26%) after transvaginal sonography was performed. The use of transvaginal ultrasound should be seriously considered when the placenta appears to be low or over the internal cervical os by transabdominal ultrasound.