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.