Prenatal Vitamins: What You Need Each Trimester

A good diet comes first, but a few nutrients are hard to get from food alone in pregnancy. That is why most providers recommend a daily prenatal vitamin. Here is what to look for, and how your needs change as your baby grows.

When should I start taking prenatal vitamins?

Ideally at least one month before you try to conceive, and as soon as you find out you are pregnant if you hadn't started. The neural tube, which becomes your baby's brain and spinal cord, forms in the first four weeks after conception, often before you know you are pregnant.

What to look for on the label

A standard prenatal vitamin should contain at least:

Nutrient	Typical daily amount	Why it matters
Folic acid	400 to 800 mcg	Prevents neural tube defects like spina bifida
Iron	27 mg	Supports your growing blood volume and prevents anemia
Iodine	150 mcg	Supports your thyroid and your baby's brain
Vitamin D	600 IU (15 mcg)	Bones, immune system and mood
Calcium	200 to 300 mg (top up from food to 1,000 mg)	Your baby's skeleton, and protecting yours
Choline	Around 450 mg (often low in vitamins)	Brain and spinal cord development

Avoid supplements with high-dose vitamin A (retinol), as too much can harm a developing baby. Prenatal formulas are made to be safe.

First trimester: folic acid first

Folic acid is the single most important supplement in early pregnancy. It is critical in the first 12 weeks, when it prevents neural tube defects. If you have had a previous pregnancy affected by a neural tube defect, have diabetes or take certain epilepsy medicines, your doctor may prescribe a higher dose (often 4 to 5 mg).

Vitamin D also matters now: a large share of pregnant people are low in it, and it supports immunity, mood and your baby's early bone development. Iodine supports your thyroid and your baby's developing brain from the very first weeks.

If your prenatal makes nausea worse, take it with a snack at bedtime, or ask your provider about a folic acid-only tablet until the sickness eases.

Second trimester: iron and calcium

Iron and folate needs climb as your blood volume expands by up to 50%. Anemia is the most common second-trimester deficiency, and it can leave you exhausted. Your provider will check your iron, and may add a separate iron supplement if you are low.

Your baby's skeleton is hardening fast. If you don't eat much dairy or fortified food, a calcium supplement can fill the gap. Take calcium and iron at different times of day, as calcium blocks iron absorption.

Third trimester: iron, DHA and magnesium

Iron demand is highest now: your baby is building iron stores to last their first six months outside the womb. Keep taking your prenatal right up to birth, and through breastfeeding.

DHA, an omega-3 fat, supports your baby's brain and retinas, which grow fastest in the third trimester. Oily fish twice a week or an algae-oil supplement are both effective.

Some people take magnesium for night leg cramps and sleep. Check with your provider before adding it.

Extra supplements for vegans and vegetarians

Plant-based diets can absolutely support a healthy pregnancy, with a few additions:

Vitamin B12 is found only in animal products. A supplement is essential for vegans, as deficiency can cause lasting harm to a baby's nervous system.
DHA: plant omega-3 (ALA from flax, chia and walnuts) converts to DHA very poorly, so an algae-oil supplement is the reliable option.
Iodine: seaweed has very variable iodine levels, so it isn't a dependable source. Make sure your prenatal contains iodine.
Zinc: compounds in legumes and whole grains reduce zinc absorption, so check your prenatal covers it.
Calcium: even with fortified foods, vegan diets often fall short of 1,000 mg a day.

Read more in our guide to a vegan or vegetarian pregnancy.

Frequently asked questions

Can I take a regular multivitamin instead of a prenatal?

It is better to choose a prenatal. Regular multivitamins may not have enough folic acid or iron, and some contain too much vitamin A.

What is the difference between folate and folic acid?

Folate is the natural form found in food. Folic acid is the synthetic form used in supplements and fortified foods, and it is the form proven to prevent neural tube defects. Methylfolate is another form some prenatals use; ask your provider if you are unsure which is right for you.

Do prenatal vitamins cause constipation?

The iron in prenatals can. Drinking more water, eating more fiber and moving every day help. If it is a problem, ask your provider about a different formula.

Always confirm supplement choices with your doctor or midwife before starting.

Sources

General information only, not medical advice. Always follow the guidance of your doctor or midwife.

History of updates

October 21, 2026: Published.