Riboflavin concentration in maternal and cord blood in human pregnancy.

Riboflavin concentration was measured in sera of a control population and in a series of paired maternal and cord sera. The assay technique was carefully validated and appears to be specific and reproducible. The mean riboflavin concentration in 12 apparently healthy adults was 116 +/- 46 nmol/L (SD). In 20 uneventful pregnancies the cord serum concentration was generally higher than the maternal concentration (158 +/- 47 nmol/L versus 113 +/- 35 nmol/L; p = 0.001). The cord-to-maternal ratio in paired sera averaged 1.45 +/- 0.44. There was no detectable difference in binding of riboflavin to cord and maternal serum proteins as measured by equilibrium dialysis (59.0% +/- 17% versus 60.8% +/- 16%). Comparison of protein binding by paired cord and maternal sera yielded a ratio of 0.99 +/- 0.13. The transplacental gradient of riboflavin concentration is unrelated to protein binding and is consistent with active transport by the placenta, as previously demonstrated in vitro.