Sonographic umbilical cord morphometry and coiling patterns in twin-twin transfusion syndrome

Monochorionic twins with twin-twin transfusion syndrome (TTTS) provide an ideal model in which to evaluate the influence of differing hemodynamic stress on umbilical cord (UC) morphology. The purpose of this study was to investigate the UC morphometry and UC coiling pattern at ultrasound in monochorionic twin pregnancies with TTTS.

A targeted sonographic evaluation of the UC was performed in 21 consecutive twin pregnancies with untreated TTTS. The cross-sectional area of the UC and of its vessels was measured. The Wharton's jelly area was computed by subtracting the vessels area from the area of the UC. The umbilical coiling index (UCI) was calculated as the reciprocal of the sonographic length of one complete vascular coil. The UCs were classified as uncoiled, normally coiled, hypocoiled, hypercoiled and atypically coiled (UCI not valuable).

The UCs of recipient twins were invariably larger than those of donors, and this difference was mainly attributable to both a larger amount of Wharton's jelly and a larger umbilical vein diameter. The proportion of lean UCs was higher in the donor than in the recipient fetuses (18/21 vs 1/21, p < 0.0001), while large UCs were significantly more frequent in the recipient than in the donor twins (13/21 vs 1/21, p = 0.0002). In all twin pairs, a discordant umbilical coiling pattern was observed between the donor and the recipient twin. The prevalence of uncoiled and hypocoiled cords was higher in the donor group, while hypercoiling and atypical coiling were more frequently detected in the recipient group.

A discordant UC morphometry represents an additional phenotypic feature of twins with TTTS. The discordant intertwin coiling pattern in TTTS argues against an exclusively genetic origin of UC twists, and further supports a key role of hemodynamic forces in coiling development.