Prenatal vitamins: what you actually need and when to start

Reviewed by Emma Carter, Senior Health & Nutrition Editor

Pregnancy supplements are surrounded by marketing, but the evidence points to a short, clear list. You do not need a cupboard full of pills. Two supplements have strong backing, a couple of things are worth avoiding, and the rest is mostly food. Here is what actually matters and when to start.

The two that matter

For most women, two supplements carry the real evidence in pregnancy.

These are the UK figures: the NHS advises 400 micrograms of folic acid daily for the first 12 weeks, and 10 micrograms of vitamin D daily from early October to late March, or year-round if you get little sun or have darker skin (NHS). National guidance differs, so if you are outside the UK, follow your own country's advice and your midwife or doctor.

Folic acid reduces the risk of neural tube defects such as spina bifida, which form in the first few weeks. A Cochrane review of randomized trials found that folic acid, alone or with other vitamins and minerals, prevents neural tube defects, though it showed no clear effect on other birth defects (Cochrane review, 2015). Vitamin D supports the baby's developing bones and your own, and shortfalls are common, especially in winter. A simple pregnancy multivitamin that contains both covers the essentials. There is no need to spend a fortune; the dose is what counts, not the brand.

Folic acid: the timing is everything

The neural tube forms and closes in the first weeks after conception, often before a pregnancy is confirmed. That is why folic acid is started early, ideally about three months before trying to conceive, and continued to the end of week 12.

Most women take 400 micrograms a day. A higher 5 milligram dose is prescribed by a doctor for women at increased risk, for example with diabetes, certain blood conditions, some medicines such as epilepsy treatments, or a previous pregnancy affected by a neural tube defect (NHS). That higher dose is a medical decision, not something to self-prescribe.

What about iron and everything else

A standard prenatal covers the two essentials. Beyond that, more is not better.

• Iron is added only if a blood test shows you are low or anemic, not taken by default. Our guide to iron in pregnancy covers how much you need and when to supplement; if you are prone to low levels, see also iron, iron deficiency and iron-rich foods.
• Omega-3 and calcium are best met from food for most women. Oily fish, dairy, fortified foods and leafy greens do the work; see calcium and omega-3 for detail.
• Megadose multivitamins aimed at pregnancy are unnecessary and can contain too much of some nutrients. A basic pregnancy supplement is enough.

What to avoid

A few things are worth steering clear of:

• Vitamin A (retinol) supplements, including cod liver oil, and liver or liver products, because too much vitamin A can harm the baby (NHS).
• High-dose or unregulated supplements, which can deliver amounts no one has checked for pregnancy.
• Herbal supplements, unless your midwife or pharmacist has confirmed they are safe.

When to start and how to keep it simple

If you are planning a pregnancy, start folic acid now and add vitamin D. If you have only just found out you are pregnant, start both today; it is never too late to begin vitamin D, and folic acid still matters up to week 12. In the UK, some families qualify for free vitamins through the Healthy Start scheme, so it is worth asking your midwife.

Keep the routine easy: one pregnancy multivitamin with folic acid and vitamin D, taken at a time of day you will remember. If morning sickness makes swallowing a tablet hard, taking it with food or at a different time can help.

When to see your doctor or midwife

Speak to a professional if you may be at higher risk and could need the 5 milligram folic acid dose, if you have a health condition or take regular medicines, or if you are unsure whether a supplement is safe. They can tailor the advice to you, which matters more than any label on a box.

Frequently asked questions

Which prenatal vitamins do I actually need?

Two have strong evidence: folic acid, 400 micrograms a day from before conception through the first 12 weeks, and vitamin D, 10 micrograms (400 IU) a day through autumn and winter, or year-round if you get little sun. A simple pregnancy multivitamin that contains both covers the essentials for most women. You do not need a large stack of supplements.

When should I start taking folic acid?

Ideally about three months before trying to conceive, and at least from the moment you start trying, continuing until the end of week 12. The neural tube forms very early, often before a pregnancy is confirmed, so starting early is what makes folic acid work.

How much folic acid should I take?

400 micrograms a day for most women. A higher 5 milligram dose is prescribed by a doctor for women at increased risk, for example with diabetes, a higher BMI, certain medicines, or a previous pregnancy affected by a neural tube defect. Do not take the high dose without medical advice.

What should I avoid in pregnancy supplements?

Avoid supplements containing vitamin A (retinol), and liver or liver products, because too much vitamin A can harm the baby. Skip high-dose or unregulated products, and check any herbal supplement with your midwife or pharmacist before taking it.

Do I need iron or omega-3 supplements in pregnancy?

Not routinely. Iron is added only if a blood test shows you are low or anemic, rather than taken by default. Omega-3 and calcium are best met from food for most women. Your midwife will advise if your situation calls for more.

References

1. Vitamins, supplements and nutrition in pregnancy · NHS
2. Effects and safety of periconceptional oral folate supplementation for preventing birth defects · Cochrane Database of Systematic Reviews, 2015
3. Dietary supplements and life stages: pregnancy · NIH Office of Dietary Supplements