Definitions
The evidence of the umbilical cord troubles in the present study was obtained from medical records in the individual facilities. And definitions were used regarding the Glossary of Obstetrics and Gynecology published by the Japan Society of Obstetrics and Gynecology.10
Velamentous and marginal cord insertion: Velamentous or marginal cord insertion is characterized by membranous umbilical vessels at the placental insertion site. In velamentous insertion, the umbilical vessels diverge, surrounded by fetal membranes with no Wharton’s jelly at the placental end of the cord. Marginal insertion is the umbilical cord located just at the edge of the placenta.
Multiple umbilical cord entanglements: Umbilical cord entanglement is defined when one or more loops of the umbilical cord are encircled around any part of the fetus. In the present study, we included cases with two or more entanglements.
Umbilical cord constriction/thin cord: Diagnosis of umbilical cord constriction is made when the umbilical cord has one or more narrow parts by macroscopic evaluation, including umbilical ring constriction, constriction in the free loop, and thin umbilical cord without Wharton’s jelly.
True knot: A true knot of the umbilical cord is formed when the fetus passes through a loop of the umbilical cord while being active in the uterus.
Abnormal umbilical coiling: The umbilical coiling index is calculated by dividing the total number of coils by the cord’s length in centimeters. Hyper- and hypo-coiled cord after delivery are defined with umbilical coiling indices of ≥0.3 coils/cm (>90% percentile) and <0.1 coils/cm (<10% percentile).11
Single umbilical artery: Diagnosis of a single umbilical artery is made macro- or microscopically when one umbilical artery is absent or obstructed.
Umbilical cord prolapse: The umbilical cord prolapse is diagnosed clinically when the umbilical cord’s free loop protrudes into or outside the vagina.