Soernes T, Bakke T
Am J Obstet Gynecol. 1986 May;154(5):1086-7. doi: 10.1016/0002-9378(86)90756-8.
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. An already known difference between the sexes regarding cord length was also confirmed, and a difference in male:female ratio in the two presentations is shown. The results of the study thus seem to support the two stated theories.
（1）脐带长度受胎儿运动活动影响；（2）臀位与胎儿运动活动少有关。据此可以预期，与头位相比，臀位的平均脐带长度会更短。实际情况确实如此。研究还证实了已知的性别在脐带长度上的差异，并显示了两种胎位中男女性别比的差异。因此，该研究结果似乎支持上述两个理论。
