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Background Maternal vitamin B12 (B-12) adequacy is important for maternal health and optimal fetal growth. However, pregnancy-specific cut-offs for B-12 biomarkers are lacking. Methods Reference intervals for serum total B-12, holotranscobalamin (holoTC) and methylmalonic acid (MMA) concentrations were calculated following CLSI EP28-A3c guidelines in 723 pregnant women of European (50%) and South Asian (50%) ethnicity, residing in British Columbia, Canada, at median (range) 11.4 (8.3-13.9) and 16.1 (14.9-20.9) weeks of gestation. Change point analyses described relationships between log serum MMA concentration with serum total B-12 and holoTC concentrations, assuming linear-linear relationships. Results The central 95% reference interval limits indicated that serum total B-12 &lt;89.9 and &lt;84.0 pmol/L, holoTC &lt;29.5 and &lt;26.0 pmol/L and MMA &gt;371 and &gt;374 nmol/L, in the first and second trimesters, respectively, may indicate B-12 deficiency in pregnant women. The lower limits of total B-12 and holoTC and the upper limits of MMA significantly differed by ethnicity in both trimesters. According to the change point analysis, total B-12 &lt;186 and &lt;180 pmol/L and holoTC &lt;62.2 and &lt;67.5 pmol/L in the first and second trimesters, respectively, suggested an increased probability of impaired intracellular B-12 status, with no difference between ethnicities. Conclusions We present novel reference limits and change points for B-12 biomarkers, which may be employed to identify possible B-12 deficiency in women during early and mid-pregnancy. Future research is needed to validate these cut-offs and determine the predictors and functional outcomes associated with impaired B-12 status in ethnically diverse populations.

clinical chemistry and laboratory medicine (cclm)

Reference intervals for serum total vitamin B12 and holotranscobalamin concentrations and their change points with methylmalonic acid concentration to assess vitamin B12 status during early and mid-pregnancy