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Why Conventional Reference Ranges Don't Stack up in Pregnancy

Updated: Jan 4, 2023


Reference ranges on a pathology report from a laboratory are determined by men or non-pregnant women. If you've followed or worked with me for long enough you'll also know that standard reference ranges are not reflective of optimal health or function, they typically represent the general population minus the bottom and top five percent. Therefore, it logically makes no sense to compare a pregnant female striving for optimal health against a standard lab reference range. It's not just logic or my opinion however, there is research to conclude that most analytes change during pregnancy thus it's important to use specific reference ranges during pregnancy.


The Physiology

It doesn't take a degree in health sciences to appreciate that many physiological changes are taking place during pregnancy. Most of these changes take place very soon after conception and continue well into late gestation. It's the adaptations taking place to accomodate the needs of mother and baby that also result in many signifiant changes in pathology values. This article won't outline all implicated pathology but I do want to highlight some key values to be aware of including liver function panel, CRP, iron studies, full blood examination, electrolytes, thyroid and lipids.


Iron Deficiency Anaemia (IDA)

In my clinical experience, the tests causing the most concern, worry and confusion are iron studies and full blood examination. This is not to downplay how critical it is to prevent and/or treat IDA in pregnancy (a discussion for another time), but the expected reductions in ferritin, haematocrit and haemoglobin are well documented. This is referred to as physiologic or dilutional anaemia of pregnancy and it's critical that both iron studies and full blood examinations are interpreted with a trimester specific understanding of this.


You Are Your Biggest Advocate!

If you're pregnant or thinking about becoming pregnant it's important that you advocate for yourself. If you're planning on becoming pregnant please remember that your pathology results would ideally be reflective of what's optimal for the best chances of conception, a healthy pregnancy and a healthy baby.


If you are pregnant and working with a Dr, Midwife, OBGYN, Nutritionist and/or Dietitian be sure to ask specifically about how your results stack up relative to pregnancy and trimester specific reference ranges. You shouldn't even have to ask, but because very few laboratories provide clinicians with pregnancy and trimester specific reference ranges it's up to the individual clinician to interpret the results and hopefully the interpretation is based on evidence based, trimester specific ranges.


I truly believe that conceiving, growing, birthing and raising a healthy baby takes a team, a village. If you'd like my support and want me on your team I’m taking new clients in the clinic and virtually so please reach out. Book a Complimentary 15-minute Discovery Call to get started.


References

Larsson, A., Palm, M., Hansson, L.-O. and Axelsson, O. (2008), Reference values for clinical chemistry tests during normal pregnancy. BJOG: An International Journal of Obstetrics & Gynaecology, 115: 874-881. https://doi.org/10.1111/j.1471-0528.2008.01709.x


Accessed 13/10/22: https://www.uptodate.com/contents/normal-reference-ranges-for-laboratory-values-in-pregnancy#H2

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