The Roach muscle bundle and umbilical cord coiling.

OBJECTIVE: To determine if presence of the Roach muscle, a small muscle bundle lying just beside the umbilical artery, contributes to umbilical cord coiling.

METHODS: 251 umbilical cords were examined. The umbilical coiling index (UCI) was calculated as the number of coils divided by the cord length in cm. Cords were classified as hypocoiled (UCIp90). On microscopic examination of a cross section of the cord, absence or presence of a Roach muscle was determined. The t-test for independent samples and logistic regression were used for statistical analysis.

RESULTS: A Roach muscle was observed in 101 cords. The mean UCI was higher in cords with the muscle bundle (0.23 coils/cm) than in cords without a muscle (0.18 coils/cm). Difference in mean: 0.05 coils/cm (95% C.I. 0.01-0.09). OR for hypercoiling in presence of the muscle was 2.98 (95% C.I. 1.57-5.64). OR for hypocoiling in the presence of the muscle was 1.49 (95% C.I. 0.79-2.81).

CONCLUSIONS: Our results suggest that presence of a Roach muscle bundle contributes to umbilical cord coiling. Given the divergence in umbilical cord coiling within subgroups with or without this muscle, other factors must play a more dominant role.