Is prenatal vitamins before pregnancy safe during pregnancy?

What does the evidence say about prenatal vitamins before pregnancy during pregnancy?

1. A daily prenatal vitamin is advised before pregnancy and continued afterward, and starting one before you conceive may also help with nausea and vomiting later in pregnancy. 1
2. The recommendation is a prenatal vitamin with at least 400 micrograms of folic acid, started at least one month before pregnancy and continued through the first 12 weeks. 1
3. The neural tube closes on days 21 to 28 after conception, which is why folate status before a positive test carries more weight than folate status after one. 2
4. Iodine needs rise from 150 micrograms a day to 220 in pregnancy, the American Thyroid Association advises 150 micrograms a day as potassium iodide for anyone planning a pregnancy, and an analysis of 59 best-selling prenatal multivitamins found only 34 contained any iodine at all. 3
5. Iron needs go from 18 milligrams a day for women aged 19 to 50 up to 27 milligrams in pregnancy, and about 18 percent of pregnant people in the United States have iron deficiency, rising from 6.9 percent in the first trimester to 29.7 percent in the third. 4

Is prenatal vitamins before pregnancy safe in each trimester?

• First trimester. This is the window the timing advice is built around. ACOG says to begin a daily prenatal at least one month before you conceive and stay on it through the first 12 weeks. The neural tube closes 21 to 28 days after conception, which is often before a test turns positive, so the supply needs to already be there. ACOG also notes that starting a prenatal before pregnancy may help with nausea and vomiting later on.
• Second trimester. Nutrient demands keep climbing rather than levelling off. Iron needs rise from 18 to 27 milligrams a day in pregnancy, and iodine goes from 150 to 220 micrograms. This is a sensible point to read your label line by line, because coverage of iodine in particular varies a lot between products.
• Third trimester. Keep going. Iron deficiency becomes far more common as pregnancy progresses, reaching roughly 30 percent of pregnant people by the third trimester in United States data. If your provider ordered bloodwork, let those results rather than the marketing copy drive any change to your regimen.