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.

Bibliography

Luhby AL. Observations on transfer of vitamin B12 from mother to fetus and newborn. Am J Dis Child. 1958; 96: 532- 533.

Greibe E, Andreasen BH, Lildballe DL, Morkbak AL, Hvas AM, Nexo E. Uptake of cobalamin and markers of cobalamin status: a longitudinal study of healthy pregnant women. Clin Chem Lab Med. 2011; 49(11): 1877- 1882.

Milman N, Byg KE, Bergholt T, Eriksen L, Hvas AM. Cobalamin status during normal pregnancy and postpartum: a longitudinal study comprising 406 Danish women. Eur J Haematol. 2006; 76(6): 521- 525.

Morkbak AL, Hvas AM, Milman N, Nexo E. Holotranscobalamin remains unchanged during pregnancy. Longitudinal changes of cobalamins and their binding proteins during pregnancy and postpartum. Haematologica. 2007; 92(12): 1711- 1712.

Bondevik GT, Schneede J, Refsum H, Lie RT, Ulstein M, Kvåle G. Homocysteine and methylmalonic acid levels in pregnant Nepali women. Should cobalamin supplementation be considered? Eur J Clin Nutr. 2001; 55(10): 856- 864.

Metz J, McGrath K, Bennett M, Hyland K, Bottiglieri T. Biochemical indices of vitamin B12 nutrition in pregnant patients with subnormal serum vitamin B12 levels. Am J Hematol. 1995; 48(4): 251- 255.

Morkbak AL, Poulsen SS, Nexo E. Haptocorrin in humans. Clin Chem Lab Med. 2007; 45(12): 1751- 1759.

Recommendations NN. Nordic nutrition recommendations. Integrating nutrition and physical activity. København: Nordic Council of Ministers; 2004.

Duggan C, Srinivasan K, Thomas T, et al. Vitamin B-12 supplementation during pregnancy and early lactation increases maternal, breast milk, and infant measures of vitamin B-12 status. J Nutr. 2014; 144(5): 758- 764.

Hay G, Johnston C, Whitelaw A, Trygg K, Refsum H. Folate and cobalamin status in relation to breastfeeding and weaning in healthy infants. Am J Clin Nutr. 2008; 88(1): 105- 114.