Holotranscobalamin remains unchanged during pregnancy. Longitudinal changes of cobalamins and their binding proteins during pregnancy and postpartum

We confirm a decrease in cobalamins during pregnancy, and report that the active part of cobalamins (holotranscobalamin, holoTC) remains unchanged. The decrease in cobalamins is explained by a decreased holohaptocorrin (holoHC), suggesting that holoTC rather than cobalamins should be used as a marker of vitamin B12 deficiency during pregnancy.