Could Iron Deficiency Be Affecting Your Fertility?
Iron & Fertility · Evidence-Based
Could Iron Deficiency Be Affecting Your Fertility?
A normal CBC doesn’t rule this out. Here’s what the research actually shows about iron, ferritin, and fertility outcomes.
Key Takeaways
- Iron deficiency is linked to unexplained infertility, even in women who aren’t clinically anemic — a case-control study found women with unexplained infertility were significantly more likely to have ferritin under 30 µg/L than fertile controls.
- Treating iron deficiency has been shown to meaningfully improve outcomes: a 2025 cohort study of 292 women found live birth rates roughly tripled and miscarriage rates dropped by 68% after iron infusion treatment.
- A standard CBC can look completely normal even when you’re iron deficient — ferritin and iron levels need to be tested separately, since the body prioritizes hemoglobin production over reproductive function when iron is low.
- Ferritin reference ranges have historically been set far too low in many places; some labs are now raising their “sufficient” threshold from around 10-11 µg/L to 50 µg/L, which will catch far more women who were previously told their levels were “normal.”
- Iron deficiency symptoms are wide-ranging (fatigue, brain fog, hair loss, shortness of breath, heavy periods, short luteal phases, restless legs, and more) — five or more of these symptoms is a reasonable signal to get tested.
Why We’re Talking About Iron on a Fertility Platform
Low iron doesn’t always come up in typical TTC conversations, but the research connecting it to fertility outcomes is more substantial than most people realize. Read about the research behind iron deficiency and fertility below.
The Research: Two Studies Worth Knowing About
The first is a case-control study comparing 36 women with unexplained infertility to 36 fertile controls. While median ferritin levels weren’t statistically different between the groups, women with unexplained infertility were significantly more likely to have ferritin under 30 µg/L (33.3% vs. 11.1% of controls). In a multivariate model, both unexplained infertility and abnormal thyroid antibodies were independently associated with having ferritin below that threshold, suggesting a real connection between iron status, thyroid autoimmunity, and unexplained fertility struggles.
The second is a larger, more recent 2025 cohort study out of a Helsinki fertility clinic, following 292 women under 43 with infertility and confirmed iron deficiency (ferritin ≤30 µg/L) who received IV iron infusions. After treatment, conception rates increased from 65% to 77%, live birth rates roughly tripled (a 3.2x increase), and miscarriage rates dropped by 68%. This is observational, not a randomized controlled trial, so it shows a strong association rather than definitive proof of causation — but paired with the first study, it builds a genuinely compelling case that iron status deserves more attention in fertility workups than it typically gets.
Why Iron Matters for Fertility, Mechanistically
A few key reasons iron deficiency can affect fertility:
- Thyroid and ovarian signaling. Iron is needed for proper thyroid function, and thyroid health plays a direct role in ovulation regularity.
- Oxygen delivery to eggs and the uterine lining. Hemoglobin carries oxygen to tissue, including the ovaries and endometrium. When iron is low, the body prioritizes oxygen delivery to vital organs (heart, lungs, brain) over reproductive tissue — meaning fertility-related functions are essentially deprioritized by the body’s own triage system.
- Mitochondrial energy production. The ovaries are one of the most mitochondria-dense organs in the body. Less iron availability can mean slower egg maturation due to reduced cellular energy production.
- Placental development and miscarriage risk. Early pregnancy requires a significant increase in blood volume to support placental development. Without adequate iron stores, that process can be compromised, increasing risk of early loss.
The Testing Gap: Why a “Normal” CBC Doesn’t Rule This Out
One of the most important points here is that a standard complete blood count (CBC) can look entirely normal, even in someone who is meaningfully iron deficient. That’s because the body protects hemoglobin production above almost everything else, pulling from ferritin (stored iron) reserves to do so. This means ferritin and iron levels need to be tested specifically and separately, not inferred from a normal-looking CBC alone.
Reference Ranges Are Changing (For the Better)
For a long time, ferritin reference ranges in many regions were set remarkably low. Some labs previously considered anything above 10-11 µg/L “normal” — meaning many genuinely iron-deficient women were told their labs looked fine. Newer thresholds in some labs have moved that number up to 50 µg/L as the point where deficiency should be seriously considered, with 50-100 µg/L as a healthier target range. This shift means more women are likely to actually get flagged and treated through standard care going forward.
Common Symptoms Worth Paying Attention To
Iron affects nearly every system in the body, so symptoms can be wide-ranging: fatigue, brain fog or forgetfulness, anxiety or depression, dizziness, shortness of breath (especially with exertion), workout intolerance, hair thinning, brittle or peeling nails, pale skin, dark under-eye circles, cold hands and feet, restless leg syndrome, muscle weakness or cramping, heavy or long periods, short luteal phases, irregular ovulation, getting sick frequently, unusual cravings (including for ice or non-food items), and heart palpitations. Experiencing five or more of these is a reasonable signal to get properly tested.
Know Your Numbers
Want to Know Exactly Which Labs to Run for Iron — and What Your Numbers Should Actually Look Like?
Ferritin, iron, and transferrin saturation each tell a different part of the story, and reference ranges are often far too low to catch real deficiency. Fertility Labs 101 walks you through the full lab workup used with fertility clients so you understand what’s being tested, why, and what the optimal ranges actually are.
Get Fertility Labs 101 →Sources & Further Reading
- Iron status in women with infertility and controls: a case-control study. Frontiers in Endocrinology, 2023.
- Tulenheimo-Silfvast, A., Ruokolainen-Pursiainen, L., Simberg, N. Association between iron deficiency and fertility. Acta Obstetricia et Gynecologica Scandinavica, 2025.
- Georgsen, M., et al. Low ferritin and recurrent pregnancy loss, as cited in Fertility and Sterility, 2020.
There’s a 50% Chance Male Fertility Is Keeping You From Getting Pregnant
Half of all infertility cases involve a male factor. Yet sperm testing is still the last thing most couples are told to do — and the numbers being called “normal” are far from it.
- Male factor is involved in 50–70% of infertility cases — yet sperm testing is still routinely the last step, not the first.
- The WHO’s lower limit for “normal” sperm concentration is 15 million/mL — the 5th percentile. At that level, estimated per-cycle pregnancy odds are around 5%.
- Optimal sperm concentration sits at the 50th percentile of men who successfully conceived: approximately 60–73 million/mL.
- Below 30 million/mL, pregnancy probability drops off sharply. Above 50 million/mL it plateaus near the natural per-cycle ceiling of 20–25%.
- Sperm concentration is not fixed. A targeted, data-driven approach can produce significant improvement — often within 3–6 months.
When a couple struggles to conceive, the instinct — in clinical settings and at home — is to start with her. Her cycle, her hormones, her ovulation. This is understandable. It is also costing couples months, and sometimes years, they do not need to lose.
The data is unambiguous: male factor is involved in somewhere between 50 and 70% of infertility cases. Not as a rare secondary concern — as a primary driver, half the time. Yet semen analysis is still treated as the test you run after everything else has been checked, if it gets run at all.
What the statistics actually show
Infertility is clinically defined as 12 consecutive months of trying to conceive without a pregnancy. When researchers break down the causes, the picture looks like this:
This does not change based on prior pregnancies. Sperm quality and concentration shift over time, affected by age, health, stress, illness, and lifestyle. A previous successful conception — in this relationship or a past one — is not a current result. Testing still matters.
Why “normal” doesn’t mean what it sounds like
The reference range most clinics use comes from WHO guidelines. Under those guidelines, a sperm concentration of 15 million per millilitre is considered normal. A man who hits that number is typically told everything looks fine.
What that framing leaves out: 15 million/mL is the 5th percentile. It was derived from a dataset of men who did achieve pregnancy with their partners within 12 months — but the threshold was drawn at the very bottom of that group. Ninety-five percent of those men had better numbers. The threshold was not placed where success is likely. It was placed at the floor of the range where it has occasionally been shown to work.
At 15 million/mL, the estimated per-cycle probability of conception is approximately 5%. That is the number being rubber-stamped as acceptable in clinical semen analysis reporting.
The 50th percentile of that same dataset — the midpoint of men who successfully conceived — sits around 73 million per millilitre. A practical target for optimisation is above 60 million/mL. That gap, between what clears the bar and what actually reflects fertility potential, is not a minor technical distinction. It is where most couples who are told “nothing is wrong” are quietly losing time.
Where the real drop-off happens
Pregnancy probability by sperm concentration is not a linear curve. The steepest decline happens below 30 million/mL — which is still well above the WHO minimum threshold that triggers no clinical concern.
Above 50 million/mL, per-cycle pregnancy probability plateaus near 20–25% — a ceiling that reflects biological limits, not sperm count. Getting from 60 million to 100 million makes little practical difference. Getting from 15 million to 60 million makes a significant one.
Subfertility vs. infertility — and why the gap matters
One reason male factor gets missed is that clinical concern is triggered by infertility thresholds, not subfertility. If a result clears 15 million/mL, it does not prompt a referral or a follow-up conversation. But a man at 25 million/mL is not in the same position as one at 70 million/mL — and treating those results as equivalent is how couples end up in a prolonged stretch of “keep trying” that didn’t need to last as long as it did.
Subfertility — results that are technically within range but far from optimal — is common and, in many cases, improvable. The research base for male fertility nutrition, lifestyle, and supplementation is more robust than most people realise, partly because sperm concentration is a measurable, repeatable endpoint that is straightforward to study. Randomised controlled trials exist. The evidence base is there. But it cannot be applied well without knowing what the actual numbers are.
Getting tested — and reading the results correctly
A clinical semen analysis — where the sample is produced and analysed on-site at a lab — remains the most reliable method. At-home testing has improved; one option used in fertility-focused clinical programmes is Fellow, which runs morphology and returns actual numerical data rather than a simplified pass/fail result. If at-home results come back low or irregular, confirming with a clinical sample before building any treatment plan is the sensible next step.
When results come back, the question is not just whether concentration clears 15 million/mL. It is where concentration sits relative to the 50th-percentile target. Below 60 million/mL, there is room for improvement. Below 30 million/mL, understanding why — structural, hormonal, or lifestyle-related — should come before any intervention is started.
Testing is the beginning of a plan, not the end of a conversation.
The Sperm Count Blueprint
A focused resource for anyone whose sperm concentration is below optimal — or who doesn’t yet know where it stands. Covers how to interpret your numbers, the most common reasons concentration is low, and how to build a targeted plan based on what the research actually supports.
Get the Blueprint → Includes the Full Male Lab GuideReferences
- World Health Organization. (2021). WHO laboratory manual for the examination and processing of human semen (6th ed.). WHO Press. https://www.who.int/publications/i/item/9789240030787 — Source for sperm concentration reference ranges, including the 5th percentile lower threshold of 15 million/mL used in clinical semen analysis reporting.