Iron is one of the most important nutrients in pregnancy — and one of the most consistently overlooked. By the third trimester your body’s iron requirements have nearly doubled, and around one in three Irish women will develop iron deficiency or iron-deficiency anaemia at some point during their pregnancy.
This guide is the pharmacist’s explanation of why iron matters in pregnancy, how to know if you need a supplement, why so many women struggle with tolerance, and how to take iron in a way that actually works.
Key takeaways
- Iron requirements nearly double in pregnancy — from around 15 mg to 27 mg daily by the third trimester
- Iron deficiency in pregnancy is associated with maternal fatigue, increased risk of preterm birth and low birthweight
- The HSE routinely screens for anaemia with a full blood count at booking and again at 28 weeks
- Gut side effects (constipation, nausea, stomach upset) are the single biggest reason women stop taking iron — gentler formulations exist
- Always take iron with vitamin C and away from calcium, tea and coffee to maximise absorption
Why iron requirements rise in pregnancy
Your body needs more iron in pregnancy to:
- Increase your own blood volume — plasma volume rises by 40–50% to support the developing pregnancy
- Build the baby’s blood supply and iron stores (which last the baby through the first 4–6 months of life)
- Build the placenta
- Prepare for blood loss at delivery
The combined demand is significant. The recommended daily iron intake for pregnant women is 27 mg/day — nearly double the non-pregnant requirement of 15 mg. Most women cannot consistently hit this from diet alone.
How common is iron deficiency in Irish pregnancies?
Research from Irish maternity services consistently shows around 20–35% of women develop iron deficiency at some point during pregnancy, with the highest prevalence in the third trimester. The risk is higher in women who entered pregnancy with already-depleted iron stores — a common picture in women with heavy periods, vegetarian/vegan diets, closely spaced pregnancies or a history of low iron.
Symptoms of iron deficiency in pregnancy
Many symptoms of iron deficiency overlap with normal pregnancy symptoms, which is part of why it gets missed. Pay particular attention to:
- Persistent fatigue that doesn’t lift with rest
- Shortness of breath on stairs or mild exertion
- Pale complexion, particularly inner eyelids and palms
- Brittle nails or hair shedding
- Restless legs at night — strongly associated with low iron
- Pica — unusual cravings for ice, clay, paper or chalk
- Headaches and dizziness
How iron status is tested in pregnancy
The HSE’s standard antenatal pathway includes a full blood count at booking and again at 28 weeks. This picks up anaemia (low haemoglobin) but can miss iron deficiency without anaemia, where haemoglobin is still within range but iron stores are depleted. If you have symptoms, ask your GP or midwife to add a ferritin (your iron storage marker) to your bloods.
| Marker | What it shows | Typical threshold for iron deficiency in pregnancy |
|---|---|---|
| Haemoglobin (Hb) | How much oxygen-carrying capacity is in your blood | < 110 g/L in 1st & 3rd trimester, < 105 g/L in 2nd |
| Ferritin | How much iron is stored in your body | < 30 µg/L generally indicates iron deficiency |
If your bloods come back showing deficiency, your GP or midwife will recommend a specific iron dose. Mild deficiency is typically managed with an over-the-counter oral iron supplement; significant deficiency or established anaemia may need prescription-strength iron or, occasionally, intravenous iron.
Why gut tolerance is the biggest issue with iron
The most common reason women stop taking iron in pregnancy is the side effects: constipation, nausea, abdominal cramping, dark stools and a metallic taste. Pregnancy itself already slows the gut, so an iron supplement that compounds constipation is genuinely difficult to live with.
This is why the formulation matters. Conventional ferrous sulphate, the cheapest and most prescribed form, has the highest rate of GI side effects. Newer formulations — bisglycinate, kappa-casein-coated iron, sustained-release — are designed to be gentler on the gut while still delivering bioavailable elemental iron.
Active Iron Pregnancy 60 Capsules
Iron formulated to be gentler on the gut — designed to be absorbed in the small intestine rather than irritating the stomach. Includes folic acid (400 µg) and B12 to support the pregnancy. Take only after a GP or midwife has confirmed you need iron.
Shop Active Iron Pregnancy →Active Iron Women 60 Capsules
A useful option for women trying to conceive (building iron stores before pregnancy) and for postnatal recovery after delivery, when iron losses continue. Also pairs added folate and B-vitamins.
Shop Active Iron Women →How to take iron in pregnancy — the practical detail
Once you and your GP have agreed iron is needed, these are the small details that make the difference between iron that works and iron that doesn’t:
- Take it with vitamin C. A glass of orange juice or a vitamin C tablet alongside your iron significantly improves absorption.
- Separate it from calcium. Calcium directly inhibits iron absorption. Don’t take iron with dairy, calcium supplements or your pregnancy multivitamin if it contains calcium — separate them by at least 2 hours.
- No tea or coffee within 1–2 hours. The polyphenols in tea and coffee can reduce iron absorption by 50% or more.
- Take it on an empty stomach if you can tolerate it. Iron absorbs best on an empty stomach, but if it causes nausea, take it with a small amount of food.
- Consider alternate-day dosing. Recent research suggests taking iron every other day rather than daily can improve absorption efficiency and reduce side effects. Discuss this with your GP.
- Support your bowels. Iron-induced constipation is best addressed with adequate hydration, daily walking and a daily soluble fibre like psyllium husk (1–2 hours away from your iron dose).
Iron and constipation — the gut workaround
Iron is famous for causing constipation, and pregnancy already slows gut transit. The fix is rarely to stop the iron — it’s to support the bowel alongside it. A daily soluble fibre like SylliFlor is well tolerated in pregnancy, addresses iron-induced constipation effectively and has no interactions with iron when taken at a different time of day.
SylliFlor Psyllium Husks Plain 250g
100% pure psyllium husk — well tolerated in pregnancy, addresses iron-induced constipation without medicines. Take 1–2 teaspoons daily in 250 ml water, at least 2 hours away from your iron dose.
Shop SylliFlor Plain →Frequently asked questions
Should every pregnant woman take an iron supplement?
No. Routine iron supplementation isn’t recommended for all pregnant women in Ireland. Iron should be taken if your GP or midwife has confirmed iron deficiency or anaemia on bloods, or if you have specific risk factors (heavy pre-pregnancy periods, vegetarian diet, closely spaced pregnancies, multiple pregnancy). Speak to your maternity team before starting.
Can I take iron with my pregnancy multivitamin?
Most pregnancy multivitamins contain calcium, which competes with iron for absorption. If you take both, separate them by at least 2 hours. A common routine is to take your multivitamin with breakfast and your iron supplement in the early afternoon with a glass of orange juice.
What if iron makes me constipated?
Iron-induced constipation is best addressed with adequate hydration, daily walking and a daily soluble fibre supplement like psyllium husk. Take the fibre at least 2 hours away from your iron. Alternate-day iron dosing (rather than daily) can also reduce side effects — discuss with your GP.
Is it possible to take too much iron in pregnancy?
Yes. Excess iron can cause oxidative stress and is associated with its own pregnancy complications. This is why iron supplementation in pregnancy should always be based on confirmed deficiency, not assumption. Stick to the dose recommended by your GP or midwife.
What if oral iron doesn’t work for me?
If your iron levels don’t improve on oral iron, or if you can’t tolerate any oral form, your GP or obstetrician can refer you for intravenous iron. This is increasingly used in Irish maternity services for women who don’t respond to oral iron, particularly in the third trimester.
About the author
Roisin Cahill MPharm MPSI is a PSI-registered pharmacist (Reg. 11957), Trinity College Dublin MPharm graduate and Co-Founder of RoCa Healthcare. She is Chemco Pharmacy’s gut health and women’s health specialist and co-developer of the SylliFlor® psyllium husk range.
→ Read Roisin’s full pharmacist profile