Pregnancy vitamins in the UK: folic acid before pregnancy, vitamin D, iodine and what to avoid

Vitamins when trying to conceive

The NHS and NICE recommend two supplements for everyone planning a pregnancy – folic acid 400 mcg and vitamin D 10 mcg a day. Your GP or midwife decides on anything else, based on your blood tests and medical history.

Before you conceive:

• start folic acid 400 mcg a day – NICE suggests ideally 3 months before you start trying;
• take vitamin D 10 mcg (400 IU) a day in autumn and winter;
• check your cupboard: stop supplements with retinol (vitamin A), cod liver oil and herbal remedies;
• tell your GP about any regular medicines – some change the folic acid dose you need.

Folic acid before pregnancy: dose and timing

Folic acid lowers the risk of neural tube defects – serious conditions affecting the baby’s brain and spine, such as spina bifida. The neural tube forms in the first weeks of pregnancy, which is why you start before conception.

• Dose for everyone: 400 mcg a day, from before conception to the end of week 12 (NHS, NICE).
• If your pregnancy wasn’t planned: start as soon as you find out.
• 5 mg a day only on prescription. The NHS and NICE list these situations between them: a neural tube defect in you, the baby’s biological father, your family or a previous pregnancy; type 1 or type 2 diabetes; anti-epilepsy, HIV or other medicines that affect folate; sickle cell disease or thalassaemia.
• A higher BMI alone doesn’t need a higher dose. NICE’s 2025 guidance says 400 mcg is enough if your BMI is 25 or more.

Add up the folic acid from all your supplements. NIH ODS sets the adult upper limit at 1,000 mcg a day from supplements and fortified foods. This matters if you take a pregnancy multivitamin plus separate folic acid, or inositol with added folic acid.

Methylfolate (5-MTHF) is absorbed at least as well as folic acid, but NHS and NICE advice is specifically about folic acid. If someone suggests methylfolate, check the dose with your GP.

Pregnancy vitamins: what and how much

Vitamin D in pregnancy

The NHS advises 10 mcg (400 IU) of vitamin D a day in pregnancy and while breastfeeding, between September and March. NICE advises taking it all year if you have darker skin, and the NHS adds people who cover their skin outdoors or spend a lot of time indoors. Don’t take more than 100 mcg (4,000 IU) a day, as it could be harmful. Our vitamin D3 guide explains the forms.

Healthy Start vitamins

If you’re eligible for Healthy Start (England, Wales and Northern Ireland), you can get free vitamins during pregnancy and until your baby’s first birthday. According to NICE, the tablets contain 400 mcg of folic acid plus vitamins C and D, and you take one a day. If you don’t qualify, some NHS services still offer or sell them.

Iodine: where advice differs

Iodine is needed for the mother’s thyroid hormones and the baby’s brain development. Needs rise in pregnancy: the US figure is 220 mcg a day and WHO suggests 250 mcg, from food and supplements combined. The American Thyroid Association recommends a 150 mcg potassium iodide supplement if you’re planning a pregnancy, pregnant or breastfeeding.

NHS pregnancy advice doesn’t list iodine among routine supplements. Good food sources include sea fish, dairy and eggs. So it’s worth asking your midwife, especially if you eat little dairy or fish.

What to avoid:

• iodine supplements without advice if you have a thyroid condition or take antithyroid medicines;
• kelp and seaweed supplements: NIH ODS reports 16–2,984 mcg of iodine per gram of seaweed, so the dose is unpredictable;
• going over the upper limit: 1,100 mcg a day in the US.

Iodine outside pregnancy is covered in our guide to selenium and iodine supplements.

Iron in pregnancy: only after a blood test

Your iron needs rise in pregnancy (the US value is 27 mg a day). But the NHS doesn’t list iron as a routine supplement: if a blood test shows your levels are low, your GP or midwife will advise iron.

Iron supplements often cause constipation and nausea. NIH ODS links doses of 45 mg a day or more with stomach side effects, and taking iron with food can help. Calcium may reduce iron absorption, so take them at different times. Our guide to iron tablets compares the forms.

Vitamin A and retinol: what to avoid

Too much preformed vitamin A (retinol) can cause birth defects. NIH ODS sets the upper limit at 3,000 mcg a day, including in pregnancy and breastfeeding. The NHS and NICE go further:

• don’t take supplements containing vitamin A (retinol) or cod liver oil;
• avoid liver and liver products such as pâté;
• check standard multivitamins: NICE warns they may contain retinol (look for retinyl palmitate or retinyl acetate on the label).

Beta-carotene, which your body converts to vitamin A as needed, isn’t known to cause birth defects. More in our guide to vitamins A and E.

Omega-3 and fish oil in pregnancy

A 2018 Cochrane review (70 trials, nearly 20,000 women) found that long-chain omega-3s lowered the risk of premature birth. Births before 37 weeks fell by 11%, and before 34 weeks by 42%. EFSA suggests an extra 100–200 mg of DHA a day in pregnancy, on top of the usual 250 mg of EPA+DHA.

In pregnancy, the NHS advises no more than 2 portions of oily fish a week. If you eat little fish, ask your midwife about a DHA supplement. Fish body oil or algae oil are the options; cod liver oil is not. See how to choose fish oil to read the label.

Herbal remedies and “natural” products

According to the NHS, not all “natural” remedies are safe in pregnancy. Some herbal products are of poor quality and may contain other substances, such as lead. The NHS also advises against herbal remedies if you’re trying to get pregnant.

In practice:

• herbal teas, blends and extracts only after talking to your midwife or GP;
• tell your midwife about every supplement, including homeopathic and aromatherapy products;
• supplements don’t replace antenatal care.

Who needs a different plan

• With diabetes, epilepsy, HIV treatment, sickle cell disease or thalassaemia, you need a different folic acid dose, prescribed by your GP.
• Methotrexate and anti-epilepsy medicines affect folate, so get medical advice.
• With a thyroid condition, take iodine and iron only on medical advice.
• If you’re vegan, talk to your midwife about B12: breastfed babies of vegan mothers can become deficient too.
• If you have PCOS and take inositol, tell your GP; our inositol guide explains the evidence.

How to choose on iHerb

Before a pregnancy multivitamin goes in your basket, go through its label line by line:

1. Start with folic acid 400 mcg and vitamin D 10 mcg, separately or in one pregnancy multivitamin.
2. Check there’s no retinol in the formula (retinyl palmitate, retinyl acetate, vitamin A as retinol).
3. Add up folic acid across all bottles: no more than 1,000 mcg in total unless prescribed.
4. Add iron or iodine only after talking to your midwife or GP.
5. For DHA, choose fish body oil or algae oil, never cod liver oil.
6. Take a photo of the labels and show your midwife at your next appointment.

For general advice outside pregnancy, see supplements for women; for reading the label, our Supplement Facts guide.