Pattern of vitamin B12 and folic acid during pregnancy.

The aim of this study was to evaluate folate and vitamin B12 serum concentrations and their reciprocal relationships during pregnancy in relation to gestational age and levels of hemoglobin. Serum levels of vitamin B12 (B12) and folic acid (FA) were assessed by RIA in 213 women between the 6th and 43rd week of pregnancy. For 195 of these subjects, hemoglobin and hematocrit values were available. The logarithm (log) of B12 levels was found to be inversely correlated with weeks of pregnancy (R = -0.261; p < 0.001). A decrease in B12 levels occurred before the 27th week and was significant only in the subgroup of patients having hemoglobin levels above 11 g/dl. The log FA concentrations did not show any significant correlation with weeks of pregnancy irrespective of Hb levels. There was also a highly significant correlation between log B12 and log FA after 27 weeks and in the subgroups divided according to Hb levels (< or = and > 11 g/dl). It is therefore concluded that: (1) the demand for vitamin B12 is high in the first 27 weeks of pregnancy due to increasing maternal and embryo-fetal erythropoiesis and in order to sustain normal maternal Hb levels in the last weeks of pregnancy; (2) vitamin B12 might favor the absorption and utilization of FA after 27 weeks of pregnancy.