Pregnancy-specific reference ranges for haematological variables in a Scottish population.

Using laboratory reference ranges, B₁₂ deficiency is inappropriately diagnosed and treated in pregnancy. We aim to define reference ranges for ferritin, folate, haemoglobin and B₁₂ in a pregnant population with advancing gestation. A total of 190 women participated in a cross-sectional study, 113 in the 1st and 77 in the 3rd trimester. All variables studied except red cell folate, decreased significantly from the 1st to the 3rd trimester. A total of 34% (64/190) of women were found to have 'low' B₁₂ as defined by traditional ranges. In women with anaemia and apparent B₁₂ deficiency, co-existing ferritin deficiency was demonstrated. All women with 'low' B₁₂ levels were invited to attend postnatally for re-testing. A total of 28% (18/64) attended, in whom all B₁₂ levels spontaneously increased. The use of gestation specific reference ranges for haematological variables may reduce inappropriate diagnosis of B₁₂ deficiency. In most women with apparent low B₁₂ levels and anaemia, ferritin deficiency was demonstrated. Therefore iron should be the initial management therapy.