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

Using laboratory reference ranges, B(12) deficiency is inappropriately diagnosed and treated in pregnancy. We aim to define reference ranges for ferritin, folate, haemoglobin and B(12) 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' B(12) as defined by traditional ranges. In women with anaemia and apparent B(12) deficiency, co-existing ferritin deficiency was demonstrated. All women with 'low' B(12) levels were invited to attend postnatally for re-testing. A total of 28% (18/64) attended, in whom all B(12) levels spontaneously increased. The use of gestation specific reference ranges for haematological variables may reduce inappropriate diagnosis of B(12) deficiency. In most women with apparent low B(12) levels and anaemia, ferritin deficiency was demonstrated. Therefore iron should be the initial management therapy.