Supplements in Pregnancy

Q: I am pregnant and have been told I need to take an iron supplement. Is this true for all pregnant women?

A: Most women need extra iron during pregnancy because blood volume increases and the demand for nutrients grows. While not every pregnant woman will require a supplement, iron deficiency is very common and testing is the safest way to know your individual needs.

WHY IRON MATTERS IN PREGNANCY

Iron deficiency is the most widespread mineral deficiency, particularly among women. In South Africa, a large screening of 4 636 people found that 52% were iron-deficient. According to the World Health Organization, around 35% of pregnant women are likely to become iron-deficient in their first trimester, rising to 85% by the third.

Women carrying twins, vegetarians, or those with closely spaced pregnancies are at greater risk. Iron deficiency during pregnancy is linked to around 20% of infant deaths worldwide.

HOW MUCH IRON DO YOU NEED?

  • Non-pregnant women: 1.5 to 2 mg absorbed per day

  • Second trimester: 2 to 4 mg absorbed per day

  • Third trimester: 3 to 6 mg absorbed per day

This is almost triple the requirement for non-pregnant women. Because absorption from food is often only 5 to 20%, most people need a dietary intake of about 14 mg daily to meet requirements.

SYMPTOMS OF IRON DEFICIENCY

  • Fatigue

  • Dizziness and shortness of breath

  • Headaches, palpitations, altered taste

  • Difficulty swallowing if long-term

TESTING AND MONITORING

A simple blood test can check your iron status and is available at most pharmacies and clinics.

WHAT AFFECTS ABSORPTION?

Many foods and drinks can block iron absorption, including tea, coffee, soft drinks, red wine, dairy products, and high-bran cereals. This is why supplements are best taken on an empty stomach, away from meals and these inhibitors.

CHOOSING SUPPLEMENTS

Newer forms of iron such as liquid iron water or chelated iron are better absorbed than traditional iron salts and often avoid side effects like constipation or stomach irritation. Some prenatal multivitamin formulations combine iron with folic acid, calcium, and other essential nutrients for pregnancy.

Recent research continues to deepen our understanding of iron supplementation in pregnancy, revealing new considerations beyond basic guidelines:

  • A large 2025 Oxford review found that daily oral iron supplementation in non-anaemic pregnant women can still prevent iron deficiency anaemia, with one case of anaemia avoided for every ten women who take supplements.

  • A 2025 cohort study (Jiangsu Birth Cohort) discovered that heme iron intake in late pregnancy, from food sources, was associated with a 35% reduction in the risk of non-optimal cognitive development in infants by age one, whereas non-heme or supplemental iron showed no such effect.

  • At the Society for Maternal-Fetal Medicine (SFMF) 2025 meeting, one of the largest trials to date (over 4 300 participants in India) reported that intravenous iron administered in early second trimester was both safe and effective in treating moderate iron deficiency anaemia, offering a promising alternative when oral supplements are poorly tolerated.

  • Finally, the U.S. Preventive Services Task Force (USPSTF) recently reaffirmed that evidence remains insufficient to recommend routine screening or supplementation for iron deficiency in asymptomatic pregnant women, emphasising the importance of individual risk assessment rather than blanket recommendations.

These findings underscore the importance of personalising iron care in pregnancy, testing first, choosing appropriate sources (food vs. supplement vs. IV), and focusing on balance rather than routine dosing.

Supplements in Pregnancy

A WORD ON IRON INFUSION IN PREGNANCY

For women who cannot tolerate oral iron, or in cases of moderate to severe iron-deficiency anaemia, an intravenous (IV) iron infusion may be recommended. This involves delivering iron directly into the bloodstream through a drip.

When it’s considered:

  • Oral supplements cause severe side effects such as nausea, constipation, or stomach pain.

  • Iron deficiency is diagnosed late in pregnancy and quick replenishment is needed.

  • Severe anaemia is confirmed and oral iron would not correct levels fast enough.

Benefits:

  • Rapidly restores iron stores and raises haemoglobin.

  • Bypasses digestive absorption problems.

  • Reduces the risk of complications for both mother and baby when anaemia is significant.

Risks and considerations:

  • Infusion must be given in a medical setting, usually a hospital or specialist clinic.

  • Possible side effects include headache, dizziness, or allergic reaction (rare).

  • Cost is higher than oral supplements, and access may be limited in some areas.

Latest evidence (2025):
A large Indian trial of over 4 300 pregnant women showed that IV iron in the early second trimester was both safe and effective for treating anaemia, offering a valuable option where oral iron failed.

Editor's note: For more on pregnancy read Pregnancy and Child Birth  and Keys to a Healthy Pregnancy.

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