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

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

Hayes, DJL (1), Warland, J (2), Parast, MM (3), Hasegawa, J (4), Banks, J (1), Clapham, L (1), Bendon, RW & Heazell, AEP (1).

(1) Tommy’s Stillbirth Research Centre, University of Manchester, UK; (2) St Marianna University School of Medicine, Japan; (3) University of California, San Diego USA; (4) University of South Australia.

Background
Current data on the role of umbilical cord complications are conflicting; estimates of the proportion of stillbirths due to cord accidents range from 3.4 to 10.1%. Various abnormalities including true knots, cord entanglements, and abnormal coiling of the cord may be associated with stillbirth. We have undertaken a systematic review to determine which cord abnormalities are associated with stillbirth, and identify sources of variation between studies.

Methods
Literature searches were performed in MEDLINE, EMBASE, CINAHL, and Google Scholar. Studies were included if they reported singleton pregnancies after 20 weeks’ gestation with no congenital abnormalities. Cohort or cross-sectional studies were included if they reported the frequency of umbilical cord characteristics or cord abnormalities and their relationship to stillbirth.

Results
271 full text papers were identified after screening according to our inclusion and exclusion criteria. Of these, 23 contained usable data on the relation between cord abnormalities and stillbirth. Nuchal cords were present in 21% of deliveries and there was no evidence of an association with stillbirth when data were pooled (odds ratio (OR) 1.36, 95% confidence interval (CI) 0.72, 2.58; 42,866 pregnancies from 13 studies). Comparing multiple loops of nuchal cord (present in 4% of births) to single or no loops gave an OR of 2.36 (95% CI 0.99, 5.62; 6 studies). We were not able to look at the effect of tight or loose nuchal loops. The likelihood of stillbirth with a true cord knot found after birth was significantly higher than in those without (OR 3.96, 95% CI 1.85, 8.47; 911,814 pregnancies from 7 studies). Stillbirth was also increased in hypercoiled umbilical cords compared to normal (OR 4.62, 95% CI 2.44, 8.75; 2346 pregnancies from 3 studies).

Conclusions
Stillbirth is associated with cords with true knots and hypercoiled cords at delivery, the incidence of stillbirth is higher with multiple nuchal loops.

Ethics statement
Ethics approval not required

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