May 2021
Dr John-Hein Knoblauch – Chemical Pathologist
Ampath | ampath.co.za
What is Anaemia in Pregnancy?
Defined by haemoglobin (Hb) levels (WHO and ACOG):
- First trimester: Hb < 11 g/dL
- Second trimester: Hb < 10.5 g/dL
- Third trimester: Hb < 10.5–11 g/dL
- Postpartum: Hb < 10 g/dL
Prevalence:
- ~30% of women of reproductive age have anaemia
40% of pregnant women are affected globally (WHO)
- Most common cause: Iron deficiency due to low or absent iron stores
Iron Deficiency vs. Iron Deficiency Anaemia (IDA)
- Many pregnant women have iron deficiency (ID) without anaemia
- IDA is the second-most common cause of anaemia after physiological anaemia
- Estimates suggest 30–60% of pregnant women have ID without anaemia
Causes of Iron Deficiency During Pregnancy
- Inadequate dietary iron intake
- Blood loss from menstruation, prior pregnancies, or short pregnancy intervals
- Increased demand for iron due to:
- Expanding maternal blood volume
- Foetal RBC production
- Placental growth
- Conditions that reduce iron absorption or intake, such as:
- Nausea and vomiting
- Inflammatory bowel disease
Health Risks of IDA in Pregnancy
Maternal:
- Increased risk of death due to haemorrhage and sepsis
Foetal:
- Low birth weight
- Double the risk of preterm birth
- Long-term cognitive and growth impairment
Who Should Be Screened for Iron Deficiency?
All anaemic pregnant women and high-risk non-anaemic women should be screened.
High-risk factors include:
- Previous ID diagnosis
- Diabetes mellitus (DM)
- Smoking
- HIV infection
- Inflammatory bowel disease
- Multiparity
- Abnormal uterine bleeding
- Obesity or underweight
- Vegetarian diet
Screening and Diagnosis
Primary test:
- Serum ferritin level
- <30 ng/mL indicates iron deficiency
- Sensitivity: 90%
- Specificity: 85%
When to do additional testing:
- If inflammation is present (ferritin = acute phase reactant)
- If ferritin is borderline or normal in high-risk or symptomatic patients
In these cases, request a full iron study including:
- Ferritin
- Serum iron
- Transferrin
- Transferrin saturation
Diagnostic Guidelines
- Ferritin <30 ng/mL confirms iron deficiency
- Ferritin >30 ng/mL usually excludes ID (except in inflammatory conditions)
- Ferritin 30–40 ng/mL = borderline
- Ferritin up to 100 ng/mL may still indicate ID in:
- Chronic illness (e.g. DM)
- Chronic kidney disease
- Autoimmune diseases like SLE or RA
- Pregnancy with acute phase response
In these cases, transferrin saturation <20% supports iron deficiency diagnosis
(<16% without inflammation, <20% with inflammation)
Important Note About Supplementation
- Oral iron can transiently increase serum iron, falsely elevating transferrin saturation
- To avoid this:
- Perform iron studies after an overnight fast
- Avoid iron supplements or iron-rich meals before testing
Requesting Tests from Ampath
Use the following mnemonics when ordering:
- FERP – Ferritin (Pregnancy)
- FEPP – Iron studies (Pregnancy profile)
Key Takeaways
- Anaemia and iron deficiency are common and clinically significant in pregnancy
- Iron deficiency can exist without anaemia and must be treated
- Serum ferritin is the preferred screening tool
- Ferritin <30 ng/mL is a widely accepted threshold
- Borderline or high ferritin may require full iron studies due to ferritin’s acute-phase nature
References
- Auerbach M. UpToDate, 2021
- Daru J. Transfusion Medicine, 2017
- Frayne J. Australian Journal of General Practice, 2019
- Marcewicz L. Maternal Child Health Journal, 2017
- Van den Broek NR. British Journal of Haematology, 1998
- UpToDate, 2021 – Reference ranges in pregnancy
📌 For clinical support, contact your local Ampath pathologist.
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