Maternal and fetal plasma levels of pyridoxal phosphate at term: adequacy of vitamin B6 supplementation during pregnancy.

The effect of different amounts of vitamin B6 supplementation during pregnancy on maternal and fetal plasma levels of pyridoxal phosphate (PLP) at term has been studied. Ten of 13 subjects given 2 to 2.5 mg. of vitamin B6 daily exhibited plasma PLP levels lower than 4.7 ng. per milliliter (the lower limit of normal for nonpregnant subjects). In contrast, only 4 of 11 subjects given a supplement of 10 mg. of vitamin B6 daily had plasma PLP less than this value. The mean plasma PLP level (64.4 ng. per milliliter) of 10 cord blood samples from newborn infants whose mothers exhibited plasma PLP levels greater than 4.7 ng. per milliliter was significantly higher (P less than or equal 0.005) than that (34.2 ng. per milliliter) from 14 newborn infants whose mothers had abnormally lowered plasma PLP concentrations. In cord plasma, an average venous-arterial gradient of 10.6 ng. per milliliter was observed, indicating that the fetus retains and/or degrades PLP. These results suggest that more than 2 to 2.5 mg. of vitamin B6 supplement daily is required for most pregnancies to restore normal vitamin B6 nutrition in the mother and, perhaps, also in the fetus.