Velamentous cord insertion: results from a rapid review of incidence, risk factors, adverse outcomes and screening

Abstract

Background: Velamentous cord insertion (VCI) is an umbilical cord attachment to the membranes surrounding the placenta instead of the central mass. VCI is strongly associated with vasa praevia (VP), where umbilical vessels lie in close proximity to the internal cervical os. VP leaves the vessels vulnerable to rupture, which can lead to fatal fetal exsanguination. Screening for VP using second-trimester transabdominal sonography (TAS) to detect VCI has been proposed. We conducted a rapid review investigating the quality, quantity and direction of evidence available on the epidemiology, screening test accuracy and post-screening management pathways for VCI.

Methods: MEDLINE, Embase and the Cochrane Library were searched on 5 July 2016 and again on 11 October 2019, using general search terms for VP and VCI. Only peer-reviewed articles reporting on the epidemiology of VCI, the accuracy of the screening test and/or downstream management pathways for VCI pregnancies were included. Quality and risk of bias of each included study were assessed using pre-specified tools.

Results: Forty-one relevant publications were identified; all but one were based on non-UK pregnancy cohorts, and most included relatively few VCI cases. The estimated incidence of VCI was 0.4-11% in singleton pregnancies, with higher incidence in twin pregnancies (1.6-40%). VCI incidence was also increased among pregnancies with one or more other risk factors, including in vitro fertilisation pregnancies or nulliparity. VCI incidence among women without any known risk factors was unclear. VCI was associated with adverse perinatal outcomes, most notably pre-term birth and emergency caesarean section in singleton pregnancies, and perinatal mortality in twins; however, associations varied across studies and the increased risk was typically low or moderate compared with pregnancies without VCI. In studies on limited numbers of cases, screening for VCI using TAS had good overall accuracy, driven by high specificity. No studies on post-screening management of VCI were identified.

Conclusions: Literature on VCI epidemiology and outcomes is limited and low-quality. The accuracy of second-trimester TAS and the benefits and harms of screening cannot be determined without prospective studies in large cohorts. Modelling studies may indicate the feasibility and value of studying the epidemiology of VCI and the potential impact of detecting VCI as part of a population screening programme for VP.

Keywords: Abnormal placental cord insertion; Adverse pregnancy outcomes; Obstetrics; Screening; Ultrasound; Vasa praevia; Velamentous cord insertion.

Fig. 1

PRISMA flow summary of the rapid review results. *Given the focus of this review, only the eligibility criteria relating to VCI were applied. [a] Searches for full-text articles were carried out at Cambridge University Library. Some articles were not freely available at this library. One article (Francois 2003 (ref [10] in Supplementary References)) was included on the basis of the abstract alone, but for the remainder of the articles, it was judged that they would not contain any additional pivotal data from relevant populations that would affect the conclusions of this review. [b] Eight articles (original) and two articles (update) were hand-searched, but not included in their own right. [c] Two would also have been excluded for country if they were not already excluded for date

Fig. 2

The association between VCI and various pregnancy characteristics. Numbers in italics were calculated by the review authors. Low cord insertion is umbilical cord insertion in the lower third of the uterus, or not visible [36].^†Odds ratio (unless stated otherwise) of the pregnancy characteristic in pregnancies with and without VCI. ^‡p value of the odds ratio. [a] Adjusted odds ratio. [b] Relative risk. IVF, in vitro fertilisation; NR, not reported; VCI, velamentous cord insertion

Fig. 3

Incidence and risk of adverse perinatal outcomes in pregnancies with and without VCI. Numbers in italics were calculated by the review authors. Increased/decreased risk indicates increased/decreased with VCI, respectively. ^†p value of the odds ratio unless stated otherwise. ^‡Unless stated otherwise. ^§p value for the difference in incidence unless stated otherwise. *Odds ratio calculated by the reviewer. ^#Weighted number of cases (adjusted for missing data) presented. [a] Adjusted odds ratio. [b] Mean (SD). CS, caesarean section; DC, dichorionic; IUFD, intrauterine fetal death; MC, monochorionic; MCDA, monochorionic diamniotic; MCMA, monochorionic monoamniotic; NR, not reported; NS, not significant; PC, paracentral; SD, standard deviation; SGA, small for gestational age; TTTS, twin-twin transfusion syndrome; VCI, velamentous cord insertion