Vasa Previa

Abstract

Vasa previa refers to unprotected fetal vessels running through the membranes over the cervix. Until recently, this condition was associated with an exceedingly high perinatal mortality rate attributable to fetal exsanguination when the membranes ruptured. However, ultrasonography has made it possible to diagnose the condition prenatally, allowing cesarean delivery before labor or rupture of the membranes. Several recent studies have indicated excellent outcomes with prenatally diagnosed vasa previa. However, outcomes continue to be dismal when vasa previa is undiagnosed before labor. Risk factors for vasa previa include second-trimester placenta previa and low-lying placentas, velamentous cord insertion, placentas with accessory lobes, in vitro fertilization, and multifetal gestations. Recognition of individuals who are at risk and screening them will greatly decrease the mortality rate from this condition. Because of the relative rarity of vasa previa, there are no randomized controlled trials to guide management. Therefore, recommendations on the diagnosis and management of vasa previa are based largely on cohort studies and expert opinion. This Clinical Expert Series review addresses the epidemiology, pathophysiology, natural history, diagnosis and management of vasa previa, as well as innovative treatments for the condition.

Evolution from placenta previa to Type‐3 vasa previa

“…Delivery by Cesarean section prior to rupture of the membranes largely prevents perinatal death [4][5][6] . Several studies have documented the feasibility of screening routinely for vasa previa and the impact of screening in preventing death 4,7,8 . Consensus guidelines recommend sonographic examination of the placental cord insertion when feasible 4 .…”

“…Several studies have documented the feasibility of screening routinely for vasa previa and the impact of screening in preventing death 4,7,8 . Consensus guidelines recommend sonographic examination of the placental cord insertion when feasible 4 . While most early reports indicated that vasa previa results from velamentous cord insertion, Catanzarite and colleagues first described in 2001 Type-2 vasa previa, in which the cord insertion was normal but unprotected fetal vessels ran through the membranes between the main placental mass and an accessory lobe 9 .…”

“…It has been hypothesized previously that some cases of vasa previa arise when placental tissue overlying the cervix in a pregnancy with placenta previa or a low-lying placenta undergoes atrophy with advancing gestation 4 . Indeed, studies indicate that approximately 60% of patients with vasa previa at delivery had a low-lying placenta or placenta previa in the second trimester 4,6,11 . This report illustrates that merely identifying the placental cord insertion is insufficient to screen for vasa previa.…”

A 2‐cm Distance Should Not Be Used to Define Vasa Previa

“…

V asa previa refers to exposed unprotected fetal vessels that run through the membranes over the cervix. 1,2 This condition is associated with a high risk for perinatal death when not detected prenatally. [3][4][5] However, vasa previa is a condition that demonstrates the remarkable impact of ultrasound in dramatically improving perinatal outcomes.

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“…However, no such safety has ever been demonstrated for vaginal delivery with vasa previa. 2 Yet, some publications continue to define vasa previa as fetal vessels that lie within 2 cm of the internal os. In the absence of any data to support this distance as being safe, one wonders why so many adopt this distance definition.…”