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.