Length of the human umbilical cord in multiple pregnancy

The factors controlling the length of the human umbilical cord are uncertain. In the generally accepted 'tension theory', the length of the umbilical cord is proposed to increase the tensile force on it in the uterus. The greatest tensile force is supposed to be fetal movement. If this is so, the length of the umbilical cord should be shorter in multiple pregnancy than in single pregnancy. To examine this possibility we measured the umbilical cord lengths in 3314 singleton births, 82 twins births (164 infants), and 11 triplet or quadruplet births (35 infants). The cord lengths in multiple pregnancies (twins 51.3 cm, triplets and quadruplets 50.1 cm) tended to be shorter than that in singleton pregnancies (57.2 cm). However, no significant difference was found in the ratio of the umbilical cord length to the infant body weight in these groups. Therefore, we conclude that an important factor in determining the cord length is the size of the infant.