Folic Acid, Iodine, and Vitamin D: Key Nutrients in the First Trimester

The first 13 weeks of pregnancy are a time when many body systems are forming. That is why three nutrients come up so often: folic acid, iodine, and vitamin D.

Why folic acid matters

Folic acid is the synthetic form of folate, a B vitamin. Getting enough folic acid before conception and in early pregnancy lowers the risk of neural tube defects. These are serious problems with the brain and spinal cord.

The neural tube forms very early, often before many people know they are pregnant. That is why folic acid is usually discussed before conception or as soon as pregnancy is confirmed.

• The CDC and ACOG recommend 400 micrograms (0.4 mg) of folic acid daily for most people who could become pregnant.
• If you have a higher risk, such as a previous pregnancy affected by a neural tube defect, your provider may recommend a higher dose.
• Folate also supports red blood cell formation and cell growth, both of which are very active in early pregnancy.

Why iodine is important

Iodine is needed to make thyroid hormones. These hormones help the baby's brain and nervous system develop, especially in the first trimester.

Iodine needs rise during pregnancy because your body is supporting both you and the baby. ACOG recommends 220 micrograms of iodine daily during pregnancy. Many prenatal vitamins include iodine, and your provider may suggest a supplement if your diet does not meet this need.

• Iodine intake may be low if you do not use iodized salt or rarely eat seafood or dairy.
• If you have thyroid disease, your provider will decide separately whether iodine is appropriate for you.
• Too much iodine can also affect thyroid function, so avoid high-dose supplements unless your provider recommends them.

What to know about vitamin D

Vitamin D helps your body absorb calcium and supports bone health. During pregnancy, it also plays a role in immune function and the baby's bone development.

There is no one-size-fits-all plan. Your vitamin D level depends on sun exposure, diet, skin tone, season, body weight, and whether a blood test shows a deficiency.

• In the US, the daily recommended amount during pregnancy is 600 IU (15 micrograms). Many prenatal vitamins contain part or all of this amount.
• Providers often check vitamin D when sun exposure is limited or when the risk of deficiency is higher. Higher doses are usually based on blood test results.
• Taking very high doses without medical guidance is not advised, because vitamin D can build up to unsafe levels.

What this often looks like in practice

In early pregnancy, care usually focuses on a clear basic plan rather than many single supplements. This often means a prenatal vitamin, plus extra supplements chosen based on your diet and lab results.

• Folic acid, as the key early preventive nutrient.
• Iodine, if it is not coming in enough from your diet or prenatal vitamin.
• Vitamin D, especially if a deficiency is likely or confirmed by testing.

When to talk with your provider about supplements

Some situations make an early nutrition review more important.

• Thyroid disease or treatment for a thyroid condition.
• A previous pregnancy affected by a neural tube defect.
• A restrictive diet, a vegan eating pattern, or severe nausea and vomiting.
• Low vitamin D on a blood test.
• Taking several supplements at once, which can lead to doubling up on some nutrients.

Warning signs

Supplements rarely cause emergency symptoms by themselves. However, some symptoms need prompt medical attention.

• Severe or worsening vomiting that makes it hard to eat or drink.
• Symptoms that could point to thyroid problems, such as marked fatigue, racing heartbeat, tremor, unusual sleepiness, or strong anxiety.
• Severe pain, bleeding, or a sudden change in how you feel at any stage.
• Unusual reactions after starting a supplement, such as rash, swelling, or stomach pain.

The bottom line

Folic acid, iodine, and vitamin D are the three nutrients most often discussed in early pregnancy. Folic acid helps prevent neural tube defects, iodine supports the thyroid and the baby's brain development, and vitamin D supports bones and overall health. The best plan depends on your diet, lab results, and personal risk factors, so ask your provider or midwife which supplements are right for you.

Learn more

• NIH: Pregnancy (NICHD)
• CDC: Pregnancy

General information only; it does not replace advice from your doctor or midwife.