Frequency of spontaneous resolution of vasa previa with advancing gestational age

Vasa previa is a serious obstetric complication that can result in fetal hemorrhage and death on spontaneous labor. Suggested management for vasa previa is elective hospitalization and cesarean delivery before spontaneous labor. There is little reported evidence of the rate of vasa previa resolution over the course of gestation. Identification of the resolution rate and of factors predictive of resolution potentially could improve clinical management and patient counseling.

The purpose of this study was to identify the resolution rate of vasa previa across gestation and to determine clinical and sonographic factors that are associated with vasa previa resolution.

We conducted a retrospective cohort study of all women who were diagnosed with vasa previa in a single ultrasound unit between 2005 and 2018. Vasa previa was defined as a fetal vessel within 2 cm of the internal cervical os on transvaginal sonography. The primary outcome was vasa previa resolution, defined as migration of the vasa previa to >2 cm away from the internal os.

One hundred women with vasa previa that had been diagnosed at a mean gestational age of 22.8±4.9 weeks were included. Thirty-nine women (39.0%; 95% confidence interval, 30-49%) had resolution of vasa previa at a mean gestational age of 28.6-4.7 weeks. Factors that were associated with vasa previa resolution were an earlier gestational age at diagnosis (adjusted odds ratio, 6.10; 95% confidence interval,1.92-19.40), vasa previa did not cover the internal os at diagnosis (adjusted odds ratio, 8.29; 95% confidence interval, 2.79-24.62), and vasa previa was not the result of a resolved placenta previa (adjusted odds ratio, 2.85; 95% confidence interval, 1.01--8.03). One woman with a dichorionic twin pregnancy and vasa previa resolution (at 31 weeks gestation; fetal vessels located 2.8 cm from the internal os) presented at 33 weeks with massive bleeding and fetal death of twin A. It was unclear whether the death was related to vasa previa or placental abruption.

Thirty-nine percent of vasa previas in our population resolved over the course of pregnancy. Earlier gestational age at diagnosis, vasa previa not covering the internal os, and not having a resolved placenta previa all are associated independently with an increased likelihood of vasa previa resolution. Women with vasa previa should be observed serially to assess for vasa previa resolution, because many will resolve in the third trimester.