Folic acid, vitamin D and planning a pregnancy

SASian Anderson, Writer and editor, MyGLP. Sources checked 5 November 2026.

Why folic acid comes first

Folic acid lowers the chance of neural tube defects in your baby. The NHS advice puts as much weight on timing as on dose. The NHS pregnancy vitamins page says to take 400 micrograms every day before you get pregnant and until you are 12 weeks pregnant. If you did not take it before conceiving, start as soon as you find out.

Who needs the higher 5mg dose

A 5mg dose needs a prescription from your GP. The NHS lists these reasons for it:

• You or your partner have a neural tube defect.
• You have had a previous pregnancy affected by a neural tube defect.
• You or your partner have a family history of neural tube defects.
• You have diabetes.
• You take medicine for epilepsy.
• You take antiretroviral medicine for HIV.

What changed for a BMI of 30 or more

For years, women with a BMI of 30 or more were told to take 5mg. The Royal College of Obstetricians and Gynaecologists set this out in its 2018 guideline on obesity in pregnancy, Green-top Guideline 72. The NHS medicines summary of that guideline records the advice: 5mg daily, from at least a month before conception through the first trimester.

In 2025, NICE reviewed the evidence for its maternal and child nutrition guideline, NG247. The committee found no evidence supporting high-dose folic acid for BMI alone. It agreed the standard 400 microgram dose is enough unless you have another risk factor, and said women with a BMI in the obesity range will no longer be advised to take 5mg for weight alone.

Your GP or midwife may follow older local guidance and suggest 5mg. What matters is starting early and taking it every day. If you hear two different answers, you are entitled to ask which guideline each one comes from.

Vitamin D alongside

The NHS recommends 10 micrograms of vitamin D a day while pregnant and breastfeeding, at least from September to March. If you have dark skin, cover most of your skin outdoors or spend most of your time indoors, you may need it all year. Do not take more than 100 micrograms (4,000 IU) a day. If you are pregnant or have a child under 4 and get certain benefits, or you are pregnant and under 18, the NHS Healthy Start scheme gives you free vitamins, plus help with milk, fruit and vegetables. If you are not eligible, ask your midwife. Some NHS services still hand out vitamins free or sell them cheaply.

If you already take a vitamin D dose prescribed by your GP, ask before adding another product on top.

If you take a weight loss medicine

The leaflets are clear on pregnancy. The Mounjaro leaflet says it should not be used during pregnancy because the effects on an unborn child are not known, and recommends contraception while you use it. Both Wegovy leaflets say the same for semaglutide. Plan the stop date first, then start folic acid alongside it, so both are in place before you stop contraception.

None of the weight loss medicines are used in pregnancy. Our fertility and pregnancy guide covers what to do if you find out you are pregnant on the medicine. The short version of the stop dates:

• Mounjaro (tirzepatide): the NHS tirzepatide page says stop at least 4 weeks before you start trying.
• Wegovy injection: the Wegovy pen leaflet says stop at least 2 months before.
• Wegovy pill: the Wegovy tablets leaflet gives the same 2 months.
• Foundayo: read your leaflet and ask your prescriber before you plan the date.

Keep using contraception until the stop gap has passed. On Mounjaro the pill can absorb less after starting and after each dose rise. The Mounjaro leaflet advises a barrier method, or a switch to a non-oral method, for 4 weeks each time. Our contraception guide has the detail.

A three-month plan

1. Three months before trying: book a GP or practice nurse appointment. Ask about folic acid dose, any regular medicines, and whether your cervical screening is up to date.
2. From now: take folic acid and vitamin D every day.
3. Two months before trying if you take Wegovy, or 4 weeks if you take Mounjaro: take your last dose. Keep using contraception through the gap.
4. When the gap is over: stop contraception and start trying. Carry on with folic acid until 12 weeks of pregnancy.

Appetite comes back when the medicine stops. Keep the eating habits you built: protein at each meal, plenty of fibre and regular fluids. Our protein guide still applies. Losing weight may also restart ovulation, especially with PCOS, so a pregnancy can come sooner than expected. Our PCOS guide explains why.

Sources

1. Vitamins, supplements and nutrition in pregnancy (NHS)
2. Maternal and child nutrition (NG247): rationale and impact (NICE, 2025)
3. Care of women with obesity in pregnancy (Green-top Guideline 72) (RCOG, summarised by NHS Specialist Pharmacy Service)
4. Tirzepatide: pregnancy and breastfeeding (NHS)
5. Mounjaro KwikPen patient information leaflet (Eli Lilly, via the electronic medicines compendium)
6. Wegovy pre-filled pen patient information leaflet (Novo Nordisk, via the electronic medicines compendium)
7. Wegovy tablets patient information leaflet (Novo Nordisk, via the electronic medicines compendium)