Longitudinal Concentrations of Vitamin B12 and Vitamin B12-binding Proteins during Uncomplicated Pregnancy

AbstractBackground: Because reference values for vitamin B12 concentrations and vitamin B12-binding capacities for pregnant women have not been established, the reference values for nonpregnant women are often applied to assess vitamin B12 status. The aim of the present study was to describe ranges of biochemical indices of vitamin B12 status, including red blood cell (RBC) vitamin B12, saturated and unsaturated cobalamin-binding proteins, and binding capacities in all trimesters of uncomplicated pregnancy.Methods: A total of 39 healthy pregnant women with long-term daily intake of vitamin B12 >2.6 μg/day and uncomplicated pregnancies participated in the study throughout their pregnancies. RBCs and serum vitamin B12, holo-haptocorrin, unsaturated cobalamin-binding proteins, unsaturated and total vitamin B12-binding capacities, total homocysteine (tHcy), and RBC count were assessed in weeks 9–12, 20–22, and 36–38 of gestation.Results: Significant changes in vitamin B12 status occurred in the course of pregnancy. Serum vitamin B12 concentrations and percentage of saturation of vitamin B12-binding proteins decreased steadily throughout pregnancy. In the third trimester, 35% of the participants had serum vitamin B12 concentrations <150 pmol/L and 68.6% had <15% saturation of total vitamin B12-binding capacities, but no women had RBC vitamin B12 concentrations <148 pmol/L. However, the decrease in these indices was not associated with reduced hemoglobin concentrations or RBC count or with increased tHcy concentrations.Conclusions: Our findings suggest that the reference values for vitamin B12 status in nonpregnant women may not be applicable to pregnant women.