Ultrasonographic study of umbilical cord twist direction during second trimester.

Objective: To explore/study/evaluate the relationships among umbilical twist direction, the degree of umbilical twist and differences of umbilical arterial diameters (UAD).

Methods: All obstetric patients presenting for prenatal care of singleton fetuses between 18 and 25 weeks gestation to a single provider (MN) from 2015 to 2018 had detailed umbilical cord Doppler measurements. Data including the cord twist direction, degree of twist and number of twists per cord segment length, and the diameters of each UA (UAD) and the umbilical vein (UVD) were extracted from the records. UAs were described as right or left depending on their position at the fetal cord insertion. Three groups were identified: Group A: right UAD > left UAD and Group B: left UAD > right UAD Group C: equal UAD. The coiling index was calculated as the inverse of the length of cord required for one complete 360 degrees wrap of the UA around the cord. According to the difference of UADs, the variables of right and left UADs, the coiling index, and frequencies of umbilical twist direction were analyzed using non-parametric methods.

Results: 485 singleton fetuses and umbilical cords were examined. The value of the antenatal coiling index in cases with left UAD greater than right was 0.43 ± 0.16, which was significantly higher than 0.38 ± 0.16 with right UAD greater than left ( = .001). There were significant differences between the two groups in the values of right and left UAD, value of right minus left UAD, absolute value between right and left UAD, antenatal coiling index, antenatal coiling index due to umbilical twist direction and frequencies of cord twist direction.

Conclusion: The direction of umbilical twist may be in part dependent on differences in diameters of the umbilical arteries, in addition to other fetal characteristics such as fetal movement, or handedness of fetus or mother, fetal hemodynamic forces and structure of muscles of umbilical vessels.