Role of placenta in maternal-fetal vitamin transfer in humans.

Vitamins B12, B6, biotin, folate, thiamine, riboflavin, pantothenate, and nicotinate were determined in maternal and fetal blood and placental tissue of normovitaminemic and hypovitaminemic mothers who disclaimed supplemental vitamin intake during pregnancy. No biotin or pantothenate deficits were observed in the gravidas. Hypovitaminemic mothers transferred less B12, folate, and B6 to the fetus and placenta than normovitaminemic mothers. Vitamins given by mouth increased maternal fetal, and placental levels of folate, but B6 increased only in maternal blood and the placenta; biotin and pantothenate increased only in fetal blood. Except for riboflavin, nicotinate, and pantothenate, the intramuscular administration of vitamins increased the levels of other vitamins in maternal and fetal blood and placental tissue. Results suggest that the placenta stores vitamins and the tissue vitamin receptors must be saturated before adequate transfer of vitamins to the fetus occurs.