Effect of umbilical ring constriction on Wharton's jelly

Objective The turgor of Wharton's jelly depends on osmotic and hydrostatic pressures. We tested the hypothesis that umbilical ring constriction has an impact on umbilical venous hemodynamics and thus on the volume of Wharton's jelly. Methods In a cross‐sectional study of 237 low‐risk singleton pregnancies, the cross‐sectional area of the fetal end of the umbilical cord was determined using sonography at 20–41 weeks of gestation. The inner area of the two arteries and the vein was also measured and subtracted from the cord area to calculate the area of Wharton's jelly. Based on the Bernoulli equation, the degree of vein constriction at the umbilical ring was assessed using the blood velocity increment at the abdominal inlet. Regression analysis and SD‐score statistics were used to construct mean values and to assess the effects. The dataset was also analyzed for gender‐specific effects. Results The umbilical cord cross‐sectional area increased with gestational age during the period 20–31 weeks, remaining essentially stable thereafter. The Wharton's jelly increased with gestational age from 20 until 31–32 weeks of gestation and remained at the same level for the rest of the pregnancy. At mid‐gestation, on average 70% of the cord cross‐sectional area was occupied by Wharton's jelly; at 31 weeks and later this value was 60%. Umbilical vein constriction was associated with reduced umbilical cord cross‐sectional area and Wharton's jelly in female fetuses ( P = 0.0007 and P = 0.003, respectively), but not in male fetuses. Conclusions Under physiological conditions, umbilical ring constriction affects umbilical vein hemodynamics, with corresponding effects on the umbilical cord cross‐sectional area and the amount of Wharton's jelly. Interestingly, the effects are gender‐specific. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.