Pregnancy Supplements: What You Need and What You Don't

The supplement industry is large and the messaging is often confusing. During pregnancy, advice can come from friends, social media, and a dizzying array of products, not all of which are necessary or safe. This guide covers what the NHS recommends, what the evidence supports, and what to approach with caution.

The Two Supplements Everyone Needs

Folic Acid

Folic acid (the synthetic form of folate, vitamin B9) is the single most important supplement to take in pregnancy. It significantly reduces the risk of neural tube defects — conditions affecting the development of the brain, spine, and spinal cord, including spina bifida.

The NHS recommendation: 400 micrograms (mcg) per day from before conception until the end of the 12th week of pregnancy.

If you are at higher risk — if you have had a previous pregnancy affected by a neural tube defect, if you have diabetes, or if you take certain medications — your GP may recommend a higher dose of 5mg per day. Always take the dose your GP advises.

It is hard to get enough folate from diet alone during pregnancy, and this is one supplement where it is genuinely important to take a pill rather than relying on food. Green leafy vegetables, beans, and fortified cereals contain folate, but absorption varies and levels in food are often insufficient to meet the increased pregnancy requirement.

Vitamin D

The NHS recommendation: 10 micrograms (10mcg) of vitamin D3 per day throughout pregnancy and breastfeeding.

Vitamin D is essential for calcium absorption, bone development, and immune function in both mother and baby. In the UK, the combination of low sunlight between October and March and the difficulty of getting sufficient vitamin D from food alone means deficiency is common — and more so during pregnancy, when demand is higher.

You can get a combined folic acid and vitamin D supplement (often sold as a basic pregnancy multivitamin) or take them separately — both approaches are fine. Many pregnancy multivitamins in the UK now include both.

Supplements That Are Optional but Often Helpful

Iron

Iron requirements increase significantly during pregnancy because your blood volume expands and the developing baby draws heavily on iron reserves. The NHS does not recommend routine iron supplementation for all pregnant women, but anaemia (iron deficiency) is one of the most common conditions diagnosed in pregnancy.

Your midwife will check your blood counts at booking and again at around 28 weeks. If your haemoglobin or ferritin is low, you will be offered iron supplements — usually ferrous sulfate, which is prescription strength. If your levels are normal, eating iron-rich foods (red meat, lentils, dark leafy greens, fortified cereals) alongside vitamin C to enhance absorption is sufficient.

Avoid taking iron supplements you have bought over the counter alongside prescribed iron — the combined dose can cause significant constipation and gastrointestinal discomfort.

Omega-3 (DHA/EPA)

Long-chain omega-3 fatty acids, particularly DHA, support fetal brain and eye development. The NHS does not formally recommend omega-3 supplementation for all pregnant women, but the evidence for DHA in pregnancy is solid, and many pregnancy supplements now include it.

From food: Two portions of fish per week — including one portion of oily fish such as salmon, sardines, or mackerel — provides a meaningful amount of DHA. If you eat fish regularly, supplementation is not essential.

If you do supplement: Choose a supplement specifically formulated for pregnancy (labelled DHA/EPA) or algae-based omega-3, which provides DHA without fish oil. Do not take cod liver oil during pregnancy — it contains very high levels of vitamin A (retinol), which can harm the developing baby at high doses.

Probiotics

There is emerging evidence that probiotics during pregnancy may reduce the risk of gestational diabetes, pre-eclampsia, and postnatal depression, as well as influencing the baby’s gut microbiome. However, the evidence is not yet strong enough for the NHS to make a routine recommendation. Probiotics are considered safe during pregnancy. If you want to take them, it is reasonable to do so — they are unlikely to harm and may help.

Magnesium

Many pregnant women are mildly low in magnesium, which is involved in hundreds of enzymatic processes. Leg cramps — a common complaint in the second and third trimesters — have been linked to magnesium deficiency, though the evidence for supplementation improving leg cramps is mixed. A standard dose of magnesium glycinate or citrate (200–300mg) is generally considered safe in pregnancy. Discuss with your midwife if you are considering it.

What to Avoid

Vitamin A (Retinol)

High doses of preformed vitamin A (retinol) are teratogenic — they can cause birth defects. For this reason:

• Do not take any supplement containing retinol during pregnancy (beta-carotene, the plant-based form, is safe)
• Do not take cod liver oil (it is very high in vitamin A)
• Do not eat liver more than once a week (liver is extremely high in retinol)
• Check your multivitamin — any pregnancy multivitamin should not contain preformed vitamin A (retinol), only beta-carotene

Herbal Supplements

Many herbal supplements and teas have not been studied during pregnancy and some are known to be harmful. Avoid taking herbal supplements in capsule or tablet form during pregnancy unless specifically advised by a healthcare professional. Herbal teas in food quantities (one or two cups of, say, peppermint or rooibos) are generally low risk, but concentrated herbal supplements are different.

Choosing a Supplement

A standard UK pregnancy multivitamin (such as Pregnacare or the own-brand pharmacy equivalent) typically contains folic acid, vitamin D, and other micronutrients at safe pregnancy doses. If cost is a concern, the NHS Healthy Start scheme provides free vitamins (containing folic acid, vitamin C, and vitamin D) to pregnant women on certain benefits.

The minimum: folic acid (400mcg/day until week 12) and vitamin D (10mcg/day throughout). Everything else is worth discussing with your midwife based on your individual diet and blood results.