Diagnosis of placenta previa by transvaginal sonographic screening at 12-16 weeks in a nonselected population

Objective: To evaluate the clinical significance of placenta previa at 12-16 weeks' gestation found by transvaginal sonographic screening. Methods: An unselected population of 6428 pregnant women was scanned by transvaginal sonography during 1993-1994 to assess the gestational age and to diagnose major fetal anomalies. The location of the placenta was also recorded systematically. If the edge of the placenta extended over the internal cervical os, this distance was measured with electronic calipers. Results: In 156 of 6428 patients (2.4%), the placental edge extended 15 mm or more over the internal cervical os at 12-16 weeks' gestation. Eight of these patients had placenta previa at delivery. Using this criterion at screening, two cases of placenta previa at delivery were missed. The frequency of placenta previa at delivery in this nonselected population was ten of 6428 (0.16%). Conclusions: The likelihood of placenta previa at delivery is 5.1% (95% confidence interval 2.2, 9.9) if the placenta extends at least 15 mm over the internal cervical os at 12-16 weeks' gestation. Copyright (C) 1997 by The American College of Obstetricians and Gynecologists.