The molecular weight of sodium hyaluronate in amniotic fluid.

The molecular weight of sodium hyaluronate in human amniotic fluid was determined by gel chromatography. Pooled samples from 16 weeks of gestation exhibited a broad molecular weight distribution (Mw = 3 X 10(5); Mn = 6 X 10(4)). Samples taken at 40 weeks showed a low molecular weight fraction (M less than 10(5) presumably of fetal origin, and a high molecular weight fraction (M greater than 10(6) which varied considerably, indicating a nonfetal origin. No hyaluronate degrading activity was detected in the fluid. In a case of renal dysplasia, only minute amounts of hyaluronate were found. These findings are in accordance with a renal excretion of a low molecular weight hyaluronate from the fetus. In 12 cases with proven neural tube defects, there was no significant difference in hyaluronate level and molecular weight compared to normal controls.