Introduction
Vasa previa is defined as placental vessels supported only by membranes, overlie the cervix, lie between the cervix and the presenting fetal part[1]. The prevalence of vasa previa is approximately 1 in 2500, but much higher among patients with low lying placenta, in vitro fertilization(IVF), or abnormal placental morphology, such as bipartite or succenturiate lobe placentas in the lower uterine segment[2]. These previa vessels are vulnerable not only to compression, which may lead to fetal anoxia, but also to laceration, which can lead to acute fetal blood loss or exsanguination[3]. That results in poor pregnancy outcomes if not diagnosed prenatally[4].
In a series of 12069 pregnancies screened, Baulies et al. were able to diagnose up to 78% of occurrences of vasa previa in asymptomatic pregnant women antenatally[5], which is the ideal time to reduce the risk of fetal bleeding and death[6]. Another search showed the rate of vasa previa visualization in ultrasonography at 15-20 weeks was 67%[7]. Thereby, vasa previa can be diagnosed antenatally, but missed diagnosis is still possible even when ultrasound is performed under the best circumstances in tertiary centers.
According to the guidelines, cesarean section should be probably accomplished for vasa previa at 34-36 weeks[8,9]. Suspected but inconclusive ultrasonography diagnosis is embarrassing, as unnecessary iatrogenic preterm labor brings more neonatal complications correlating with immaturity, while later cesarean section elevates the risk for suddenly laceration of potential vasa previa and exsanguination life-threatening to the newborn.
As severe complications and poor outcomes of potential vasa previa, when inconclusive ultrasonography results come, should find some way to reach more conclusive diagnoses. To explore the MRI assistance in diagnosing of vasa previa when inconclusive ultrasonography results come, the current study was conducted.