Sonographic evaluation of umbilical cord thickness in monochorionic diamniotic twin pregnancies

To develop a nomogram of the thickness of the umbilical cord (UC) and its components in monochorionic diamniotic (MCDA) twin pregnancies.

This prospective longitudinal study involved 47 MCDA twin pregnancies (94 fetuses) between 18 and 33 weeks of gestation. Ultrasound assessments of UC cross-sections and measurements of the umbilical cord area (UCA), the umbilical vein area (UVA), the umbilical artery area (UAA), and the Wharton jelly area (WJA) were made. The UC measurements were correlated with gestational ages. Reference values for the gestational ages of MCDA pregnancies were determined and compared with those of dichorionic twins and singletons. The cases which developed selective intrauterine growth restriction were contrasted with normal cases.

A positive correlation was found between all UC components and gestational age and fetal weight. The UCA of MCDA fetuses was significantly larger than that of DC fetuses (p < 0.001) at the expense of a larger WJA (p < 0.001) and similar to that of singleton pregnancies. The MCDA fetuses with an estimated fetal weight below the 10th percentile had a smaller UCA than fetuses with a normal estimated weight (p < 0.001).

The MCDA twins exhibited a thicker UC than that of dichorionic twins.