The umbilical cord, as a connecting bridge between two lives, plays an important role in fetal development. Though studies on the umbilical cord date back many years, extensive studies on certain umbilical cord characteristics, such as umbilical cord coiling, are rare. Cord coiling, measured by the umbilical coiling index, is a physiological phenomenon that offers resistance to external pressures. Umbilical cord coiling is a result of several factors, both environmental and genetic. However, umbilical cords sometimes coil abnormally, resulting in hypocoiling, hypercoiling, or non-coiling which have significant associations with adverse perinatal outcomes. An all-language literature search was conducted on Medline from 1970 to 2023. The following search terms were used; umbilical cord; umbilical coiling; coiling index; abnormal coiling; perinatal outcomes, and cross-referencing yielded further information. We comprehensively reviewed the literature on umbilical cord coiling, factors contributing to coiling, abnormal coiling of the umbilical cord, and the association with several factors including maternal age, gravida, gestational diabetes mellitus, pre-eclampsia, abruption, birth weight, intrauterine growth retardation, maternal iron status, small for gestational age, fetal heart rate variations, ponderal index, and sought possible explanations.
