Iron is an essential mineral that your body uses to make haemoglobin — the protein in red blood cells that carries oxygen to every tissue, including your ovaries and uterus. Growing evidence suggests that low iron stores, even without full anaemia, may affect ovulation, implantation, and early pregnancy.
If you're trying to conceive, you've probably heard plenty about folic acid and vitamin D. Iron gets far less attention — yet it's one of the nutrients women of reproductive age are most likely to run short of, largely because of monthly blood loss. Here's what the research actually shows, and what you can do about it.
- Iron supports oxygen delivery to the ovaries and uterine lining, and plays a role in ovulation, egg development, and implantation.
- In a study of 18,555 women, those who used iron supplements had a 40% lower risk of ovulatory infertility than non-users.
- Ferritin (your iron stores) can be low even when haemoglobin is normal — UK guidance treats ferritin below 30 µg/L as iron deficiency.
- A 2025 study found that treating iron deficiency in women with infertility roughly doubled the live birth rate, from 26% to 51%.
- The evidence isn't unanimous: a 2024 genetic study found no causal link between iron status and infertility, so iron is best seen as one piece of the picture.
- Test before you supplement — the NHS advises that more than 17 mg per day of supplemental iron may be harmful unless a GP recommends it.
Why Does Iron Matter for Fertility?
Iron enables your blood to carry oxygen, supports energy production in cells, and acts as a cofactor for enzymes involved in hormone synthesis and DNA production. Reproductive tissues are metabolically demanding — developing follicles, the uterine lining, and an early embryo all need a reliable oxygen and nutrient supply, which depends on adequate iron.2,7
Here's why that matters for you: cells with high metabolic rates are the first to struggle when iron runs low.7 The processes behind conception — maturing an egg each cycle, rebuilding the endometrium, and supporting an implanting embryo — are among the most energy-intensive jobs your body does, so they feel the shortfall first.
And if you've never thought of yourself as "at risk," you're far from alone — the scale of this is bigger than most people realise. The World Health Organization estimates that around 30% of women aged 15–49 worldwide — roughly 539 million women — are anaemic, with iron deficiency the leading cause.10 Reviews in the fertility literature describe iron deficiency in women of reproductive age as both underdiagnosed and undertreated.6
Can Low Iron Cause Infertility? What Does the Evidence Show?
Low iron has been linked to a higher risk of ovulatory infertility in large observational studies, and treating iron deficiency has been associated with better conception and live birth rates. However, a 2024 genetic analysis found no causal relationship, so the evidence is suggestive rather than settled.1,2,4
The most influential data come from the Nurses' Health Study II, which followed 18,555 women trying to conceive over eight years. Women who used iron supplements had a 40% lower risk of ovulatory infertility than non-users (relative risk 0.60; 95% CI 0.39–0.92).1 Here's the intriguing part: the protective association came from non-heme iron — the form found in plants, fortified foods, and supplements — while heme iron from meat showed no association.1 Researchers still aren't certain why, though it may simply reflect that supplement users were correcting an underlying deficiency.
More recent clinical data point the same way. A 2025 Finnish study followed 292 women with infertility and iron deficiency (ferritin ≤30 µg/L) who received an intravenous iron infusion. After treatment, the proportion who conceived rose from 65% to 77%, live births increased from 26% to 51%, and miscarriages fell from 28% to 13%.2 Treatment was associated with three-fold higher odds of a live birth (OR 3.19; 95% CI 2.21–4.66).2 Now, a caveat you deserve to hear: because the study was retrospective and uncontrolled, it can't prove cause and effect — but it's a striking signal, and one worth knowing if your own levels are low.
If you've been told your infertility is "unexplained," this next piece may be relevant to you. There's evidence that women in that situation are more likely to have depleted iron stores: in a Viennese case-control study, 33.3% of women with unexplained infertility had ferritin below 30 µg/L, compared with 11.1% of fertile controls.3
We owe you some honesty here, though. A 2024 Mendelian randomisation study — a genetic method designed to test causality — found no evidence that serum iron, ferritin, transferrin saturation, or total iron-binding capacity causally influence infertility in either women or men.4 So here's the most balanced way to hold all of this: iron deficiency appears to be one modifiable factor among many, most relevant for women who are actually deficient, rather than a universal fertility lever.
How Does Iron Deficiency Affect Ovulation and Implantation?
Iron deficiency can disrupt fertility through several mechanisms: impaired oxygen delivery to the ovaries and endometrium, reduced activity of iron-dependent enzymes involved in hormone production, and less metabolic support for egg maturation and implantation.2,6,7
Take ovulation first. Iron-dependent enzymes participate in steroid hormone synthesis — the chain that produces your oestrogen and progesterone. When iron runs short, some women experience irregular ovulation or anovulation (cycles where no egg is released). That fits with the Nurses' Health Study II finding that iron supplementation was specifically associated with a lower risk of ovulatory infertility.1
Now implantation. Each cycle, your uterine lining rebuilds itself — a process that demands oxygen, energy, and rapid cell division. Haemoglobin delivers that oxygen, and iron supports the DNA synthesis that rapid tissue growth requires.7 A well-supplied endometrium is better placed to support an implanting embryo, while persistent anaemia into pregnancy is associated with higher risks of miscarriage, preterm birth, and low birth weight.6,7
Pregnancy itself then raises the stakes: iron requirements increase dramatically as maternal blood volume expands and the baby develops, meaning women who start pregnancy with empty stores can slip into deficiency quickly.7 Building reserves before conception gives you a head start.
Ferritin vs Haemoglobin: Which Test Matters When Trying to Conceive?
Ferritin measures your stored iron and falls first when iron is running low; haemoglobin measures your blood's current oxygen-carrying capacity and only drops once deficiency is advanced. You can have normal haemoglobin with depleted ferritin — which is why ferritin is the more sensitive early marker when you're trying to conceive.9
Think of ferritin as your iron savings account and haemoglobin as your current account. You can keep spending normally for a while even as savings drain — but the gap eventually catches up with you.
| Marker | What it measures | Iron deficiency threshold (UK) | What it tells you |
|---|---|---|---|
| Ferritin | Stored iron | Below 30 µg/L | Earliest, most sensitive marker of depleted stores |
| Haemoglobin | Oxygen-carrying protein in red blood cells | Below ~120 g/L (non-pregnant women) | Whether deficiency has progressed to anaemia |
| Transferrin saturation | Iron available in circulation | Below ~20% | Helpful when ferritin is hard to interpret |
One caveat worth knowing: ferritin rises during inflammation or infection, so a "normal" result can occasionally mask a real deficiency. In the Viennese case-control study, median ferritin didn't differ significantly between infertile women and controls — but markedly more infertile women fell below the 30 µg/L threshold, and their transferrin saturation was lower (17.3% vs 23.9%).3 That's why GPs interpret iron results alongside symptoms and, where needed, additional markers.
Who Is Most at Risk of Low Iron?
Women with heavy periods are at the highest risk of iron deficiency, followed by those eating little or no meat, women with gut conditions that impair absorption, endurance athletes, frequent blood donors, and anyone who has recently been pregnant.6,8
Heavy menstrual bleeding deserves particular attention. It's one of the leading causes of iron deficiency in women of reproductive age, and underlying conditions such as fibroids or adenomyosis can make losses heavier still.6 If you regularly soak through protection hourly, pass large clots, or bleed for more than seven days, that's worth raising with your GP in its own right — not just for your iron.
Other higher-risk groups include:
- Vegetarians and vegans: plant (non-heme) iron is absorbed less efficiently than heme iron from meat and fish, so intakes need to be more deliberate.8
- Women with absorption issues: coeliac disease and inflammatory bowel disease both reduce iron uptake.6
- Frequent blood donors and endurance athletes: regular losses add up faster than diet replaces them.
- Women with a short gap between pregnancies: stores often haven't rebuilt after the demands of pregnancy and birth.7
- Women with unexplained infertility or recurrent miscarriage: given the case-control data showing higher rates of depleted ferritin in this group, screening is a sensible, low-cost step.3
How Can You Test Your Iron Levels in the UK?
In the UK, your GP can check your iron status with a simple blood test — typically a full blood count plus serum ferritin. The test is free on the NHS when clinically indicated, and results usually come back within about a week.9
It's a reasonable thing to ask for if you're trying to conceive and have risk factors (heavy periods, a meat-free diet, fatigue, previous deficiency) or symptoms. Common signs of low iron include tiredness, breathlessness on exertion, paler skin, hair shedding, brittle nails, headaches, and restless legs — though many women with depleted stores feel nothing at all until levels are quite low.9
Private testing is also widely available if you want numbers without a GP visit, but there's a real advantage to the NHS route: if your ferritin is low, your GP can investigate why. Iron deficiency always has a cause — heavy periods, diet, absorption, or occasionally something that needs proper investigation — and treating the number without understanding the cause can miss the point.
How Can You Improve Your Iron Levels Before Pregnancy?
Food comes first: the NHS advises that most people can meet the UK recommended intake of 14.8 mg per day (women aged 19–50) through a varied diet.8 Where a deficiency is confirmed, GP-guided supplementation restores stores more quickly — typically over 8–12 weeks, with retesting to confirm progress.9
A practical place to start is building iron-rich foods into the way you already eat — ideally as part of a broader fertility diet rich in whole foods, which is itself associated with better fertility outcomes.11
| Food (typical serving) | Iron type | Approximate iron content |
|---|---|---|
| Lean beef (100 g, cooked) | Heme | ~2.5–3 mg |
| Lentils (150 g, cooked) | Non-heme | ~4–5 mg |
| Fortified breakfast cereal (40 g) | Non-heme | ~4–8 mg (varies by brand) |
| Spinach (80 g, cooked) | Non-heme | ~1.5–2 mg |
| Tofu (100 g) | Non-heme | ~2.5–3 mg |
| Dark chocolate, 70%+ (30 g) | Non-heme | ~3–4 mg |
| Baked beans (200 g) | Non-heme | ~2.5–3 mg |
How you combine foods matters almost as much as what you eat:
- Pair plant iron with vitamin C: peppers, citrus, tomatoes, or berries in the same meal meaningfully improve non-heme iron absorption.8
- Time your tea and coffee: tannins and polyphenols inhibit iron absorption, so keep them an hour or so away from iron-rich meals.8
- Watch calcium timing: calcium competes with iron for absorption, so avoid taking calcium supplements alongside iron-focused meals.
If your GP confirms a deficiency and recommends supplements, the dosing schedule is worth getting right. Research in iron-depleted women found that a single dose taken every other day is absorbed better than daily dosing — each dose of iron raises hepcidin, a hormone that blocks further iron absorption for around 24 hours.5 Alternate-day dosing works with that physiology rather than against it, and often causes fewer stomach side effects too. Severe or unresponsive deficiency is sometimes treated with an iron infusion, as in the Finnish fertility study — but that's a clinician's call.2
One last thing worth keeping in mind: iron doesn't work in isolation. Folate and vitamin B12 partner with iron in red blood cell production, which is one reason broad-spectrum preconception support — covered in our guide to vitamins to help get pregnant — tends to make more sense for you than chasing single nutrients. Regular multivitamin use itself was associated with a lower risk of ovulatory infertility in the same cohort that produced the iron findings.12
Can You Take Too Much Iron?
Yes. Unlike many nutrients, your body has no efficient way to excrete excess iron, so unneeded supplementation can accumulate and cause harm. The NHS advises that doses above 17 mg per day of supplemental iron may cause side effects and should only be taken on a GP's advice.8
This is why "test before you supplement" is the golden rule with iron. High-dose iron commonly causes constipation, nausea, and stomach pain — unwelcome at any time, and an unnecessary burden when you're already navigating the stresses of trying to conceive. More seriously, around 1 in 10 people of Northern European ancestry carries a gene variant linked to haemochromatosis — a hereditary condition that causes iron to build up in the body — and a smaller group carries two copies, placing them at genuine risk of iron overload.13 For them, blind high-dose supplementation isn't just unhelpful; it's harmful.
It's also worth restating what the evidence does not show: there's no indication that taking iron improves fertility in women whose levels are already adequate.1,4 The benefit appears where a deficiency is being corrected. If your ferritin is comfortably above 30 µg/L, your energy is better spent on the broader foundations — egg quality, overall diet, sleep, and supporting ovulation naturally.
Frequently Asked Questions
Can low iron stop you from getting pregnant?
Low iron is unlikely to be the sole reason someone can't conceive, but it's a recognised contributing factor. Women with iron deficiency have higher rates of ovulatory problems, and in one large cohort, iron supplement users had a 40% lower risk of ovulatory infertility.1 Women with unexplained infertility are also around three times more likely to have ferritin below 30 µg/L than fertile controls.3
What ferritin level should I aim for when trying to conceive?
UK guidance defines iron deficiency as ferritin below 30 µg/L, so above 30 µg/L is the baseline goal.9 Some fertility clinics prefer to see higher levels before treatment, and the 2025 Finnish study treated women at or below 30 µg/L with notable improvements in live birth rates.2 Your GP can interpret your result in context, since inflammation can artificially raise ferritin.
Can low iron affect ovulation?
Yes — your reproductive hormones depend on iron-dependent enzymes, and iron deficiency has been associated with irregular ovulation and anovulation. The strongest supporting evidence comes from the Nurses' Health Study II, which linked iron supplementation to a lower risk of infertility caused by ovulatory disorders.1
How long does it take to restore iron levels?
With oral supplementation, ferritin typically begins improving within a few weeks, and GPs usually retest after 8–12 weeks to confirm progress.9 Fully rebuilding depleted stores can take several months. Intravenous iron works faster — in the Finnish fertility study, a single infusion raised average ferritin from 16 µg/L to around 82 µg/L.2
Should I take iron supplements if my levels are normal?
No — the evidence doesn't support iron supplementation for fertility in women with adequate levels, and excess iron can be harmful.4,8 The NHS advises staying at or below 17 mg per day from supplements unless a GP recommends more. A test costs nothing on the NHS and tells you whether iron is even relevant to your situation.
Is the iron in fertility supplements enough?
Combined preconception supplements typically contain moderate iron doses suitable for maintenance — enough to support normal levels alongside diet, but not designed to correct a significant deficiency. If your ferritin is below 30 µg/L, you'll likely need GP-guided treatment doses first, with a combined supplement as the longer-term foundation afterwards.9
Supporting Your Fertility with FertilitySmart
If you take one thing from this guide, let it be this: iron works best as part of a complete nutritional foundation for conception — alongside folate, vitamin B12, vitamin D, and the antioxidants that support egg and sperm health. For most women trying to conceive, your goal is steady, food-first iron intake with testing to catch any deficiency early. It's a small, manageable step in a journey that can feel anything but small — and it's one you can act on this week.
At FertilitySmart, we offer both fertility supplements for women and fertility supplements for men that contain key nutrients such as folate, vitamin B12, vitamin D, zinc, and CoQ10. Explore our range of evidence-based fertility supplements formulated with the nutrients discussed in this guide.
Related Reading
If iron is on your radar, these guides will help you build the fuller nutritional picture for conception.
-
A Complete Guide to Fertility Supplements (For Women & Men)
The pillar guide to how iron fits alongside the other nutrients that matter for conception. -
Should I Take Vitamins to Help Get Pregnant? 10 Supplements to Consider
Where iron ranks among the supplements with the strongest fertility evidence. -
Fertility Diet: How Nutrition Can Support Conception
The food-first foundation that determines most of your iron intake. -
Magnesium and Fertility: A Guide for Those Trying to Conceive
Another commonly depleted mineral and its role in reproductive health. -
How Does Folic Acid Help with Fertility Issues?
Iron's closest partner in red blood cell production and preconception care. -
7 Foods to Avoid While Trying to Conceive
The other half of the dietary picture: what to limit while building nutrient stores. -
Trying to Conceive at 35+: What Changes & What You Can Control
Why nutritional foundations like iron matter more as fertility naturally declines. -
How Long Do Fertility Supplements Take to Work?
Realistic timelines for nutritional changes, including iron repletion.
References
- Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Iron intake and risk of ovulatory infertility. Obstetrics & Gynecology. 2006;108(5):1145-1152. pubmed.ncbi.nlm.nih.gov/17077236
- Tulenheimo-Silfvast A, Ruokolainen-Pursiainen L, Simberg N. Association between iron deficiency and fertility. Acta Obstetricia et Gynecologica Scandinavica. 2025. doi.org/10.1111/aogs.15046
- Holzer I, Ott J, Beitl K, Mayrhofer D, Heinzl F, Ebenbauer J, Parry JP. Iron status in women with infertility and controls: a case-control study. Frontiers in Endocrinology. 2023;14:1173100. doi.org/10.3389/fendo.2023.1173100
- Guo L, Yin S, Wei H, Peng J. No evidence of genetic causation between iron and infertility: a Mendelian randomization study. Frontiers in Nutrition. 2024;11:1390618. doi.org/10.3389/fnut.2024.1390618
- Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. The Lancet Haematology. 2017;4(11):e524-e533. doi.org/10.1016/S2352-3026(17)30182-5
- Petraglia F, Dolmans MM. Iron deficiency anemia: impact on women's reproductive health. Fertility and Sterility. 2022;118(4):605-606. doi.org/10.1016/j.fertnstert.2022.08.850
- Georgieff MK. Iron deficiency in pregnancy. American Journal of Obstetrics and Gynecology. 2020;223(4):516-524. pubmed.ncbi.nlm.nih.gov/32184147
- National Health Service (NHS). Iron — Vitamins and minerals. nhs.uk/conditions/vitamins-and-minerals/iron
- National Institute for Health and Care Excellence (NICE). Anaemia — iron deficiency: Clinical Knowledge Summary. cks.nice.org.uk/topics/anaemia-iron-deficiency
- World Health Organization. Anaemia: Fact sheet. who.int/news-room/fact-sheets/detail/anaemia
- Gaskins AJ, Chavarro JE. Diet and fertility: a review. American Journal of Obstetrics and Gynecology. 2018;218(4):379-389. pubmed.ncbi.nlm.nih.gov/28844822
- Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Use of multivitamins, intake of B vitamins, and risk of ovulatory infertility. Fertility and Sterility. 2008;89(3):668-676. pubmed.ncbi.nlm.nih.gov/17624345
- National Health Service (NHS). Haemochromatosis. nhs.uk/conditions/haemochromatosis
Marina Carter
Health & Fertility Writer at FertilitySmart
Marina Carter is FertilitySmart's lead writer on fertility, preconception health, and reproductive nutrition. She translates the clinical and nutritional evidence base into honest, practical guidance for individuals and couples trying to conceive, working closely with the product team to ensure every article reflects current peer-reviewed research and the lived emotional reality of the fertility journey. Read Full Bio →