Effect of vitamin A status at the end of term pregnancy on the saturation of retinol binding protein with retinol

BACKGROUND: Vitamin A (retinol), which is required for normal fetal development and successful gestation, circulates in the blood bound to a specific protein, the retinol binding protein (RBP). Little is known about the transport and metabolism of this complex protein or about retinol status during normal human pregnancy. OBJECTIVE: The aim of this study was to assess retinol status and transport modalities of retinol in well-nourished women with normal pregnancies, a population poorly investigated compared with pathologic and malnourished pregnant women. DESIGN: The maternal blood and cord blood concentrations of retinol, vitamin E, beta-carotene, RBP, and transthyretin of pregnant French women at term (n = 27) were measured and compared with values from a nonpregnant control group (n = 27). In addition, holo-RBP (retinol bound), apo-RBP (retinol free), and total protein were assessed in both groups to enable the hemodilution occurring during pregnancy to be taken into consideration and to evaluate the extent of saturation of RBP with retinol. RESULTS: Healthy pregnant women at term had normal serum circulatory amounts of retinol, vitamin E, binding proteins, and beta-carotene. However, they had less binding of retinol to RBP (holo-RBP: 49.9% in pregnant women, 54.0% in cord blood, and 77.5% in the control group). CONCLUSION: The results of this study suggest that retinol homeostasis and transport are modified during normal human pregnancy.