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.

The length of the human umbilical cord in vertex and breech presentations.

The present study is based on two previously stated theories: (1) that the umbilical cord length is influenced by fetal motor activity and (2) that the breech presentation is associated with low fetal motor activity. From this one would expect the mean cord length to be shorter in breech presentations as compared with vertex. This was indeed found to be the case.