Transabdominal ultrasonography as a screening test for second-trimester placenta previa.
OBJECTIVE
To determine the test characteristics of transabdominal ultrasonography as a screening test for second-trimester placenta previa.


METHODS
This secondary analysis of a prospective cohort study evaluated the distance from the placental edge to the internal os (placenta-cervix distance) through both transabdominal and transvaginal ultrasonography during the anatomic survey. Patients were recruited in the Maternal-Fetal Medicine Ultrasound Unit at the Hospital of the University of Pennsylvania, an urban tertiary care center. Transabdominal placenta-cervix distance cutoffs with high sensitivity for detection of previa and low-lying placenta were identified, and test characteristics were calculated. Follow-up ultrasound data, pregnancy, and delivery outcomes for those with second-trimester previa or low-lying placenta were obtained.


RESULTS
One thousand two hundred fourteen women were included in the analysis. A transabdominal placenta-cervix distance cutoff of 4.2 cm was 93.3% sensitive and 76.7% specific for detection of previa with a 99.8% negative predictive value at a screen-positive rate of 25.0%. A cutoff of 2.8 cm was 86.7% sensitive and 90.5% specific with a 99.6% negative predictive value at a screen-positive rate of 11.4%. Only 9.8% (four of 41) of previas and low-lying placentas persisted through delivery.


CONCLUSIONS
Transabdominal ultrasonography is an effective screening test for second-trimester placenta previa. At centers not performing universal transvaginal ultrasonography at the time of the anatomic survey, evidence-based transabdominal placenta-cervix distance cutoffs can optimize the identification of patients who require further surveillance for previa.
Maternal and Child Health Research Program, Department of Obstetrics and Gynecology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania; and the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, College of Physicians and Surgeons, Columbia University, New York, New York.
Hayley S
HS
Quant
Alexander M
AM
Friedman
Eileen
E
Wang
Samuel
S
Parry
Nadav
N
Schwartz
D000005:Abdomen; D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D015999:Multivariate Analysis; D010923:Placenta Previa / Q000000981:diagnostic imaging*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011446:Prospective Studies; D012372:ROC Curve; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods*; D014621:Vagina; D055815:Young Adult