Vasa previa: Prenatal diagnosis, natural evolution, and clinical outcome

Objective: To describe the prenatal ultrasonographic diagnosis, natural evo lution, and clinical outcomes of vasa previa in a large population at a sin gle institution. Methods: We attempted to view the internal cervical os of 93,874 women with second- and third-trimester pregnancies during an 8-year period. Echogenic parallel or circular lines near the cervix, seen by gray-scale ultrasonogr aphy, raised the possibility of vasa previa. Diagnosis was confirmed by Dop pler and endovaginal studies if aberrant vessels over the internal cervical os were suspected. Abnormal placental morphology and velamentous cord inse rtion were documented if they were identified during prenatal scans. Ultras onographic findings were correlated with clinical courses, perinatal outcom es, and placental pathology examinations. Results: Eighteen cases of vasa previa were suspected at a mean (+/- standa rd deviation) gestational age of 26.0 +/- 6.3 weeks; the earliest diagnosis was at 15.6 weeks' gestation. Eight of those cases initially showed placen tal edge over the internal os and later developed vasa previa after the pla centa "receded" from the cervix. Six women had mild vaginal bleeding at a m ean gestational age of 31.3 weeks. Three women had normal late third-trimes ter scans and were allowed to have uncomplicated vaginal deliveries. The re maining subjects delivered by cesarean. There were two deaths (one fetal an d one neonatal), and minor preterm complications slightly prolonged infant hospitalizations. One set of preterm twins needed neonatal transfusions. Pa thology findings included ten cases of velamentous insertion and three case s each of bilobed placentas, succenturiate lobes, and marginal cord inserti on. Conclusion: Vasa previa was detected in asymptomatic women as early as the second trimester. Perinatal outcome was generally favorable, although sever al infants had slightly extended newborn nursery admissions due to mild com plications of prematurity. (C) 2000 by The American College of Obstetrician s and Gynecologists.