Written by Aisha Saleem, Pharmacist & Health Writer at PharmaHealths.com
Last Updated: August 2026
What u should know
• Ferritin normally declines during pregnancy due to hemodilution and rising fetal placental iron demand, so “normal” looks different by trimester.
• A 2024 study proposes trimester-specific deficiency thresholds of below 25.8 µg/L in the first trimester, below 18.3 µg/L in the second, and below 19.0 µg/L in the third, notably higher than the WHO’s current guidance.
• Untreated iron deficiency in pregnancy is linked to preterm birth, low birth weight, infant iron deficiency, postpartum depression, and breastfeeding difficulties.
• High ferritin in the third trimester carries its own risk, particularly for smaller than expected babies, so more isn’t automatically better.
What Counts as Low Ferritin in Pregnancy?
This is genuinely more complicated than a single number, and most guidance doesn’t fully explain why. The World Health Organization currently defines deficiency as ferritin below 15 µg/L, but only for the first trimester, offering no specific guidance for the second or third. A 2024 study published in Blood Advances addressed this gap directly, using physiological modeling to identify trimester specific thresholds of below 25.8 µg/L in the first trimester, below 18.3 µg/L in the second, and below 19.0 µg/L in the third. The researchers argue that the WHO’s stricter, single trimester figure likely underestimates how common iron deficiency actually is throughout pregnancy, since it was based on expert opinion rather than trimester-specific physiological data.
It’s also worth knowing that ferritin naturally drops as pregnancy progresses, even in women with adequate iron stores. This happens partly because blood volume expands faster than red blood cell mass in early pregnancy, a process called hemodilution, and partly because the growing fetus and placenta place increasing demands on maternal iron. Some research suggests a pre-pregnancy ferritin above 50 µg/L is generally needed to avoid developing deficiency during pregnancy without supplementation, which is a useful data point to discuss with your doctor if you’re planning a pregnancy.
What Are the Symptoms of Low Ferritin in Pregnancy?
Extreme tiredness, weakness, and dizziness are the most commonly reported symptoms, and they’re easy to dismiss as ordinary pregnancy fatigue. Some women also experience pica, a craving for non-food items like ice, chalk, or dirt, which is a genuinely distinctive sign worth mentioning to your doctor even though it’s less commonly discussed.
How Is Low Ferritin Checked and Diagnosed During Pregnancy?
Most maternity care includes a full blood count and ferritin check at your first appointment, generally around 10 weeks, with a repeat check around 28 weeks. A hemoglobin level below 11.0 g/dL is generally used to define anemia in pregnancy, but ferritin can be low well before hemoglobin drops that far, which is exactly why testing ferritin directly matters rather than relying on hemoglobin alone.
Can Low Ferritin Affect My Baby?
Yes, and the risk list is broader than most people realize. Iron deficiency during pregnancy has been linked to preterm birth, before 37 weeks, low birth weight, and impaired neurological development, since the rapidly growing fetal brain has a real iron requirement of its own. Babies born to iron-deficient mothers are also more likely to have low iron stores themselves and a higher rate of infant anemia. Beyond the baby, untreated iron deficiency in the mother is linked to a higher risk of postpartum depression and breastfeeding difficulties, risks that are just as real but get mentioned far less often than the baby-focused ones.
Is High Ferritin Also a Risk in Pregnancy?
This is a genuinely underdiscussed angle, and it surprises a lot of people. A study of 362 mother infant pairs found that higher maternal ferritin measured in the third trimester was associated with a higher rate of babies born small for gestational age, and a much larger study of over 17,000 women found the same pattern, with ferritin at or above roughly 18 ng/mL in the third trimester linked to significantly higher odds of a smaller than expected baby. Researchers suggest this challenges the assumption that routine iron supplementation is automatically safe for women whose iron levels are already adequate. Separately, some clinical guidelines note that a ferritin level above 270 µg/L should prompt a repeat test and a check for inflammation, rather than being read as reassuring, since ferritin naturally rises during inflammation regardless of actual iron stores. If your hemoglobin comes back low but your ferritin is normal or high, it’s also worth asking whether other causes, like folate or vitamin B12 deficiency, have been considered, since iron may not be the right treatment in that situation.
When Is IV Iron Needed Instead of Iron Tablets?
IV iron is generally considered when oral iron hasn’t worked or isn’t tolerated. If you’re more than 36 weeks pregnant, there may not be enough time left for tablets to raise your levels before delivery, which is when IV iron becomes the more practical option. Your midwife or doctor will usually discuss this directly rather than leaving you to request it.
Conclusion
Ferritin in pregnancy isn’t a simple “higher is better” story. It naturally shifts by trimester, both low and high levels carry their own risks, and testing at the right times matters more than fixating on one number. If you have concerns about fatigue, cravings, or your latest blood test results, it’s worth raising them directly with your midwife or doctor.
Disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider regarding any medical condition.
References
• Mei Z, et al. – Physiologically based trimester-specific serum ferritin thresholds for iron deficiency in US pregnant women (Blood Advances, 2024): https://pubmed.ncbi.nlm.nih.gov/38781318/
• World Health Organization – Ferritin concentrations (ELENA): https://www.who.int/tools/elena/interventions/ferritin-concentrations
• Mayo Clinic – Iron deficiency anemia during pregnancy: Prevention tips: https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/expert-answers/pregnancy-and-iron/faq-20058349
• Leeds Teaching Hospitals NHS Trust – Iron intake in pregnancy and beyond: https://www.leedsth.nhs.uk/patients/resources/iron-intake-in-pregnancy-and-beyond/
• Rotherham NHS Foundation Trust – Iron deficiency anemia in pregnancy: https://www.therotherhamft.nhs.uk/patients-and-visitors/patient-information/iron-deficiency-anaemia-pregnancy
• NHS Greater Glasgow and Clyde (Right Decisions) – Prevention and Management of Iron Deficiency Anemia in Pregnancy and the Puerperium: https://www.rightdecisions.scot.nhs.uk/ggc-clinical-guidelines/maternity/antenatal-general/prevention-and-management-of-iron-deficiency-anaemia-in-pregnancy-and-the-puerperium-1195/
• Thaichana P, et al. – Maternal Serum Ferritin Levels in Third Trimester and Risk of Small for Gestational Age in Northern Thailand (Nutrients, 2025): https://pmc.ncbi.nlm.nih.gov/articles/PMC12735463/
• Frontiers in Nutrition – Maternal serum ferritin across gestation and risk of small-for-gestational-age: a longitudinal cohort study: https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2026.1766451/full
