The Important Role of B12 IN PREGNANCY Leave a comment

Vitamin B12 is concentrated in the placenta and transferred to the foetus down a concentration gradient, with newborn vitamin B12 concentrations approximately double those of the mother. There is some evidence of increased B12 absorption during pregnancy, with newly absorbed vitamin B12 being more important to placental transport than maternal liver stores. However, cobalamin absorption remains unchanged during normal pregnancy, as judged by the CobaSorb test.  Post-partum, vitamin B12 concentrations spontaneously recover to preconceptional values.

Serum vitamin B12 concentration declines during pregnancy particularly in multiple pregnancies. A progressive decline in B12 status initially decreases the level of holotranscobalamin in the circulation. Subsequently, tissue stores of B12 are used and begin to diminish, leading to impaired performance of B12-dependent pathways and elevations in serum concentrations of the metabolites tHcy and methylmalonic acid MMA. Proposed explanations for the reduction in serum vitamin B12 are haemo-dilution, transportation to the foetus and redistribution of cobalamin. Serum vitamin B12 concentrations during pregnancy decline more than can be accounted for by hemo-dilution. A concomitant increase in erythrocyte cobalamin has been observed and decrease in saturation of cobalamin binding serum proteins suggests a redistribution of cobalamin during pregnancy.

The total requirement of the foetus during pregnancy is estimated to be 50 μg, while maternal stores in women with mixed diet are estimated at >1000 μg. Therefore, in well-nourished women, body stores of vitamin B12 are adequate to meet foetal needs during gestation and cobalamin deficiency in pregnancy is far less common than folate deficiency.

The recommended daily allowance for B12 increases during pregnancy from 2.4 to 6.0 μg/d.

Vitamin B12 concentrations are lower in the breast milk of mothers with deficient or marginal serum vitamin B12 status than in mothers with adequate status, though results from several studies suggest that maternal intake is a stronger predictor of breast milk vitamin B12 concentration than maternal status.


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