Conventional Pathology Reference Ranges Are Not Evidence Based for Pregnancy

All too often I work with pregnant women who have been ill-informed when it comes to their iron levels – whether that be from the incorrect prescription of Maltofer/Ferro-grad C, right up to the unnecessary recommendation for an iron infusion. Let’s take a closer look. 

When it comes to your iron studies: physiological anaemia is essential for a healthy pregnancy. Here are some key considerations in pregnancy: 

  1. We should expect a gradual decline in heamoglobin [Hb] and ferritin from about week 16 due to hemodilution. This is a good thing – increased viscosity of blood increases profusion of blood thorough the placenta to baby.
  2. Interestingly, as your levels decline your gut literally becomes like a sponge for iron, absorbing more for you and baby. Ferritin needs to be reviewed in context to Hb however as low as 15 is normal and healthy [for most labs, the standard reference range is 30-120 ug/L].
  3. At week 28 hemodilution is at a maximum so equally, expect your numbers to be lowest here. For trimester three, Hb >100 is adequate [the standard reference range is 115-165 g/L].
  4. We should also expect a gradual increase in transferrin as this increases iron delivery to the placenta. A transferrin as high as 5.0 is normal and healthy and indicates incredible iron transfer to baby [the standard reference range is 2.1-3.6 g/L].

Yet, we still use reference ranges for non-pregnant women and many women are supplementing unnecessarily, or worse, advised to have an iron infusion unnecessarily.

Quite simply, if 100mg of elemental iron is too much, what do you think an iron infusion is? Although the route is different, one infusion is 1000mg! Hint: it will suppress transferrin and this will have a negative effect on foetal transfer.

I’m curious to learn more about your experience. have you been advised an iron infusion? And was this decision based off your ferritin level alone?

For help interpreting your iron studies, please book a complimentary 15 minute Zoom consultation here:


Daru J, Allotey J, Peña-Rosas JP, Khan KS. Serum ferritin thresholds for the diagnosis of iron deficiency in pregnancy: a systematic review. Transfus Med. 2017;27(3):167-174. doi:10.1111/tme.12408

Fisher AL, Nemeth E. Iron homeostasis during pregnancy. Am J Clin Nutr. 2017;106(Suppl 6):1567S-1574S. doi:10.3945/ajcn.117.155812

Klajnbard A, Szecsi PB, Colov NP, et al. Laboratory reference intervals during pregnancy, delivery and the early postpartum period. Clin Chem Lab Med. 2010;48(2):237-248. doi:10.1515/CCLM.2010.033

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