Umbilical cord characteristics and their association with adverse pregnancy outcomes: A systematic review and meta-analysis.

Dexter J L Hayes,Alexander E P Heazell,Junichi Hasegawa,Julia Banks,Jane Warland,Mana M Parast,Laura Clapham,Robert W Bendon,Kelli K Ryckman

doi:10.1371/journal.pone.0239630

Abstract

Current data on the role of the umbilical cord in pregnancy complications are conflicting; estimates of the proportion of stillbirths due to cord problems range from 3.4 to 26.7%. A systematic review and meta-analysis were undertaken to determine which umbilical cord abnormalities are associated with stillbirth and related adverse pregnancy outcomes. MEDLINE, EMBASE, CINAHL and Google Scholar were searched from 1960 to present day. Reference lists of included studies and grey literature were also searched. Cohort, cross-sectional, or case-control studies of singleton pregnancies after 20 weeks' gestation that reported the frequency of umbilical cord characteristics or cord abnormalities and their relationship to stillbirth or other adverse outcomes were included. Quality of included studies was assessed using NIH quality assessment tools. Analyses were performed in STATA. This review included 145 studies. Nuchal cords were present in 22% of births (95% CI 19, 25); multiple loops of cord were present in 4% (95% CI 3, 5) and true knots of the cord in 1% (95% CI 0, 1) of births. There was no evidence for an association between stillbirth and any nuchal cord (OR 1.11, 95% CI 0.62, 1.98). Comparing multiple loops of nuchal cord to single loops or no loop gave an OR of 2.36 (95% CI 0.99, 5.62). We were not able to look at the effect of tight or loose nuchal loops. The likelihood of stillbirth was significantly higher with a true cord knot (OR 4.65, 95% CI 2.09, 10.37). True umbilical cord knots are associated with increased risk of stillbirth; the incidence of stillbirth is higher with multiple nuchal loops compared to single nuchal cords. No studies reported the combined effects of multiple umbilical cord abnormalities. Our analyses suggest specific avenues for future research.

Highlights

Umbilical cord abnormalities (UCA) usually describe situations where fetal blood flow is reduced or interrupted due to altered structure or function of the umbilical cord
Nuchal cords were present in 22% of births; multiple loops of cord were present in 4% and true knots of the cord in 1% of births
There was no evidence for an association between stillbirth and any nuchal cord

Summary

Introduction

Umbilical cord abnormalities (UCA) usually describe situations where fetal blood flow is reduced or interrupted due to altered structure or function of the umbilical cord. UCA are associated with adverse pregnancy outcomes including stillbirth, birth asphyxia and emergency Caesarean birth. Some of the variation may be due to the use of different classification systems for stillbirth, not all of which include UCA as a cause of death. Other UCA, including true knots and cord prolapse are rarer, but are linked to adverse outcomes; cohort studies have demonstrated associations between true knots and perinatal death and between cord prolapse and low Apgar scores [9, 10]. UCAs can present in combination, for example true knots may occur more in longer cords which are more prone to entanglement [12, 13], complicating the appreciation of the significance of individual abnormalities

Methods

Results

Conclusion