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

Abstract

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.

Keywords:

• Ferritin
• folate
• haemoglobin
• reference range
• vitamin B₁₂

Acknowledgements

Thank you to all Midwives within the antenatal clinics in Ayrshire and Arran who recruited the women, completed the paperwork and performed venesection. Thank you also to the medical secretaries for sending out the study information leaflets and finding women's medical notes.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.