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

¹ Institute of Nutritional Science, University of Giessen, D-35392 Giessen, Germany.

² German Institute of Human Nutrition, D-14558 Bergholz-Rehbrücke, Germany.

³ Department of Epidemiology, Maastricht University, 6200 MD Maastricht, The Netherlands.

⁴ Department of Haematology, Imperial College School of Medicine, St. Mary’s Campus, London W2 1PG, United Kingdom.

⁵ Department of Medical Informatics, Biometry and Epidemiology, University of Erlangen-Nuremberg, D-91054 Erlangen, Germany.

⁶ Federal Research Centre for Nutrition, D-76131 Karlsruhe, Germany.

⁷ Department of Clinical Chemistry, University Hospital Rotterdam, 3015 GD Rotterdam, The Netherlands.

^aAddress correspondence to this author at: German Institute of Human Nutrition, Arthur-Scheunert-Allee 114-116, D-14558 Bergholz-Rehbrücke, Germany. Fax 49-33200-88662; e-mail koebnick{at}mail.dife.de.

Background: 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.

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