The length of the human umbilical cord in twin pregnancies.

A current hypothesis on the linear growth of the umbilical cord states that cord length is a function of fetal intrauterine motor activity. If there is some type of intrauterine constraint, the tensile forces on the cord will be diminished, and cord length at term will be shorter than if no such constraint is present. One would expect that the voluntary movements of twins would develop under a constraint and that they would have less free space to move compared with single fetuses. If this hypothesis is valid, cord lengths of twins at term would be shorter than those of single pregnancy infants. We measured the cord lengths of 118 infants in 59 twin births and compared them with cord lengths in 9601 single pregnancies. We found that on the average, the umbilical cord length of the twins was 7.90 cm shorter than that of single pregnancy infants.