Coiling is an important property of the umbilical cord and its vessels. The helical arrangement of the umbilical vessels makes the cord both strong and flexible, permitting it to resist external forces that otherwise might compromise blood flow. This study attempted to identify any adverse pregnancy outcomes associated with under- or overcoiling of the umbilical vessels. Coiling was examined in 565 consecutive cases with an indication for histological examination of the placenta. They represented about 10% of all deliveries during the study interval from December 1998 to May 2002. The umbilical coiling index (UCI) was determined as the number of complete coils divided by the length of the umbilical cord in centimeters, as estimated by an observer without knowledge of pregnancy outcomes. Undercoiling was a UCI less than the 10th percentile, and overcoiling, an index above the 90th percentile.
Undercoiling of the umbilical cord was found in 18% of cases, and overcoiling in 13.5%. The mean UCI was 0.18, with a standard deviation of 0.12. The UCI was not associated with gestational age at delivery, infant gender maternal age or parity, smoking status, or the presence or absence of preeclampsia, gestational diabetes, or preexisting diabetes. Fetal death, chorioamnionitis, and fetal structural or chromosomal abnormalities were associated with undercoiling. The odds ratio (OR) for fetal death was 4.09, with a 95% confidence interval (CI) of 2.2-7.6. Numerous conditions were associated with overcoiling, including fetal death (OR, 3.7; 95% CI, 1.9-7.4), iatrogenic preterm delivery, an umbilical arterial pH below 7.05, fetal structural or chromosomal abnormalities, thrombosed fetal placental vessels, chronic fetal hypoxia/ischemia, and lower weight for gestational age.
Both overcoiling and undercoiling of the umbilical cord vessels are associated with adverse pregnancy outcomes. The investigators propose that the UCI be a routine part of assessing the placenta after delivery. The logical next step is a prospective study to determine the significance of under- and overcoiling of the cord vessels in an unselected population.