Prenatal diagnosis and postnatal outcome of Type‐III vasa previa: systematic review of literature

Abstract

ObjectiveVasa previa (VP) is a condition characterized by fetal blood vessels located on the amniotic membranes and outside the placenta, within 2 cm from internal os. The most common forms of VP are associated to velamentous cord insertion (type I) or to bilobed‐succenturiate placenta (type II), located across the cervix. A rare form of VP, not necessarily associated to other placental or vascular anomalies, involves aberrant vessels running from the placenta to the amniotic membranes, nearby the internal os, and then turning back to the placenta (type III). Although early diagnosis of type III VP is important, it often technically challenging and difficult. The objective of our study is to gather the current available evidence on type III VP related to prenatal diagnosis and perinatal outcome.MethodsA systematic review of the literature was carried out according to PRISMA guidelines from inception up to March 2023 using common internet‐based databases (PubMed, Scopus and EMBASE) looking for perinatal diagnosis of atypical type III vasa previa. Data extraction and tabulation was carried out by two different operators and double‐checked by a third senior author. Quality assessment of the included studies was realized using the National Institute of Health (NIH) tool for the quality assessment of Case Series Studies. Recent unpublished cases were searched in our local ultrasound database. Frequencies and proportions of prenatally vs. postnatally diagnosed type III VP were summarized, including clinical expression and perinatal outcomes.ResultsEighteen cases of type III VP were detected: 16 with prenatal diagnosis (14 from 10 publications and 2 unpublished from our center) and 2 with postnatal diagnosis from two publications. All cases with prenatal diagnosis were assessed by transvaginal ultrasound at a mean gestational age of 29 weeks (median 31 weeks; range 19‐38 weeks). Conception was achieved with IVF in 4/16 (25%), there were no prenatal symptoms in 15/18 cases (83.3%), in two cases (11.1 %) there was vaginal bleeding and in one (5.6%) preterm labour. Only 3/18 (16.6%) cases had no placental abnormality and 15/18 (83.3 %) showed at least one placental abnormality including: low‐lying insertion (9/17), succenturiate or accessory lobe (1/17), velamentous cord insertion (3/18), marginal insertion (9/18). All cases with prenatal diagnosis were liveborn with cesarean section before rupture of membranes at a mean gestational age of 35.4 weeks (range 32‐38) without neonatal complications. Emergent cesarean section was observed in 2/16 cases with prenatal diagnosis and 1/2 cases with postnatal diagnosis (rates: 12.5% vs 50%; p‐value: 0.179), Apgar score≤7 at 1 or 5 minutes in prenatally vs postnatally diagnosed cases was observed in 5/16 vs 1/2 cases (p=0.595) and 3/16 vs 1/2 cases (p=0.316), respectively.ConclusionsThe prenatal diagnosis of VP type III is challenging with few cases reported in the literature; however, it minimizes the risks of an adverse outcome with intact membranes early‐term elective cesarean delivery. Since clinical manifestations and risk factors are not specific, and type III VP cannot be excluded when there is a normal cord insertion or just one placental mass, a generalized screening by transvaginal ultrasound in the general population is recommended, particularly in presence of low‐lying or morphologically abnormal placentas and medically assisted reproduction.This article is protected by copyright. All rights reserved.

Impact of Universal Vasa Previa Screening With Color Doppler During the OB Ultrasound Anatomy Scan

“…Only a few studies have described universal transabdominal color Doppler screening using a protocol similar to ours 21,22 . Color Doppler may be especially promising for detection of Type III given that the vessels running along the surface of the placenta would be more difficult to detect with greyscale imaging alone, and more typical morphologies such as velamentous cord insertion or bilobed placenta are usually absent 7 …”

“…Three types of VP have been described in the literature, with Type I occurring in association with velamentous cord insertion and Type II occurring with a bilobed/succenturiate placenta 1,5 . More recent reports have described a third type in which aberrant fetal vessels of placental origin travel unprotected in a “boomerang” course over placental membranes near the internal os, and are thus similarly vulnerable to tearing 4,6,7 . Alternatively, some groups have sorted cases into Type I and non‐type I VP, 8 however, this may minimize meaningful differences in appearance and, consequently, detection of type II vs type III VP on prenatal ultrasound.…”

Vasa previa Type 3: Advocating for universal screening and investigation of risk factors: A case report

“… 5 Type 3 is identified by aberrant vessels extending from the placenta across the amniotic membranes adjacent to the internal cervical os, and then back to the placenta. 6 Unlike the other types, Type 3 can occur even with a normally inserted umbilical cord and without placental abnormalities. 7 …”

Evolution from placenta previa to Type‐3 vasa previa

“…A number of recent publications have described Type-3 vasa previa, a variant of vasa previa in which fetal vessels run unprotected over the cervix from one placental edge to another in a placenta that does not have a velamentous cord insertion or accessory lobes [1][2][3] . Because most cases of Type-3 vasa previa have a normal cord insertion, relying merely on the identification of a velamentous cord insertion or the presence of accessory lobes as risk factors for vasa previa will inevitably miss some cases, potentially leading to avoidable perinatal death.…”

“…In 2004, we described a variant of vasa previa in which there was a normal cord insertion and a single placental lobe, Oyelese but fetal vessels ran from one edge of the placenta to another 10 . This was subsequently termed 'Type-3 vasa previa' [1][2][3] . We hypothesized that this variant arose from placenta previa in early pregnancy, followed by atrophy of the placental tissue overlying the cervix, leaving behind unprotected fetal vessels running over the cervix 10 .…”