Objectives: To examine the feasibility and effectiveness of a two-stage ultrasound screening strategy for detection of vasa previa and to estimate the potential impact of screening on prevention of stillbirth.
Methods: This was a retrospective study of data from prospective screening for vasa previa in singleton pregnancies, undertaken at the Fetal Medicine Unit at Medway Maritime Hospital, UK, between 2012 and 2018. Women booked for prenatal care and delivery in our hospital had routine ultrasound examinations at 11-13 and 20-22 weeks' gestation. Those with velamentous cord insertion at the inferior part of the placenta at the first-trimester scan and those with low-lying placenta at the second-trimester scan were classified as high-risk for vasa previa and had transvaginal sonography searching specifically for vasa previa, at the time of the 20-22-week scan. The management and outcome of cases with suspected vasa previa is described. We excluded cases of miscarriage or termination at < 24 weeks' gestation.
Results: The study population of 26 830 singleton pregnancies included 21 (0.08%; 1 in 1278) with vasa previa. In all cases of vasa previa, the diagnosis was made at the 20-22-week scan and confirmed postnatally by gross and histological examination of the placenta. At the 11-13-week scan, cord insertion was classified as central in 25 071 (93.4%) cases, marginal in 1680 (6.3%), and velamentous in 79 (0.3%). In 16 (76.2%) of the 21 cases of vasa previa, cord insertion at the first-trimester scan was classified as velamentous at the inferior part of the placenta, in two cases (9.5%) as marginal and in three cases (14.3%) as central. The 21 cases of vasa previa were managed on an outpatient basis with serial scans for measurement of cervical length and elective Cesarean section at 34 weeks' gestation; all babies were liveborn but there was one neonatal death. In the study population, there were 83 stillbirths, none of which had evidence of vasa previa on postnatal examination. On the assumption that, if we had not diagnosed prenatally all 21 cases of vasa previa in our population, half of these cases would have resulted in stillbirth, then the potential impact of screening is prevention of 10.6% (10/94) of stillbirths.
Conclusion: A two-stage strategy of screening for vasa previa can be incorporated into routine clinical practice, and such a strategy could potentially reduce the rate of stillbirth. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.
Keywords: adverse pregnancy outcome; bilobed placenta; first-trimester ultrasound; stillbirth; vasa previa; velamentous cord insertion.
Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.