Folic acid is a vitamin that doctors recommend pregnant women take to prevent birth defects. A new study looked at reports of problems that happened after women took folic acid supplements between 2004 and 2025. Researchers found 40 cases where folic acid might have caused issues, including some serious ones like pregnancy loss and birth defects. However, these cases are very rare, and folic acid is still considered safe at the recommended dose. The study suggests we need better ways to track any problems that might happen with supplements.

The Quick Take

  • What they studied: Whether folic acid supplements taken during pregnancy might cause any harmful side effects or problems
  • Who participated: 3,866 pregnant women who reported problems after taking folic acid supplements. The study looked at reports collected by the U.S. Food and Drug Administration over 21 years (2004-2025)
  • Key finding: Out of 3,866 reports, only 40 cases suggested folic acid might be the cause of problems. Of those 40 cases, 8 happened at the normal recommended dose (0.4 mg per day). These included pregnancy loss and birth defects, though these cases are extremely rare
  • What it means for you: Folic acid remains an important and safe supplement for pregnant women at the recommended dose. However, this study suggests doctors and health agencies should keep watching for any unusual problems. If you’re pregnant or planning to be, continue taking folic acid as recommended by your doctor—the benefits far outweigh the risks

The Research Details

Researchers looked at a database called the FDA Adverse Event Reporting System, which collects reports from people who think a product caused them harm. They searched for all reports from pregnant women who said folic acid supplements caused problems between January 2004 and March 2025. They then organized these reports by type of problem (like pregnancy loss, birth defects, or early delivery) and looked at the doses women were taking when the problems happened.

This type of study is called a ‘descriptive analysis,’ which means researchers are describing what they found in the reports rather than doing a controlled experiment. They weren’t able to prove that folic acid definitely caused the problems—they could only identify cases where folic acid was suspected as a possible cause.

This approach is important because it helps catch rare problems that might not show up in regular safety studies. Most research on folic acid involves hundreds or thousands of people, so very rare side effects might be missed. By looking at real-world reports from millions of people taking supplements, researchers can spot unusual patterns. However, this method has limitations because people voluntarily report problems, and many cases might go unreported

This study has some important strengths and weaknesses to understand. The strength is that it looked at a huge amount of real-world data collected over 21 years. The main weaknesses are: (1) Many reports were incomplete—23 out of 40 cases didn’t include information about how much folic acid women were taking; (2) People might not report problems, so the real number could be higher or lower; (3) Just because a problem happened after taking folic acid doesn’t mean folic acid caused it; (4) The database relies on voluntary reports, which means serious cases might be more likely to be reported than minor ones

What the Results Show

Researchers found 40 cases where folic acid was suspected as the main cause of problems in pregnant women. This is a very small number compared to the millions of women who take folic acid safely each year. Of these 40 cases, 8 happened at the recommended dose of 0.4 mg per day, 9 happened at higher doses (more than 0.4 mg per day), and 23 cases didn’t have clear information about the dose.

The types of problems reported included pregnancy loss (miscarriage or termination), birth defects, developmental problems in the baby, early delivery, and low birth weight. The most concerning finding was that even at the recommended dose, a small number of serious problems were reported. However, researchers emphasized that these cases are extremely rare and that the overall safety record of folic acid remains very strong.

It’s important to understand that finding these reports doesn’t prove folic acid caused the problems. Many things can go wrong during pregnancy for reasons completely unrelated to supplements. The study simply identified cases where folic acid was suspected, not confirmed as the cause.

The study found that cases with unknown dosage information were common (23 out of 40 cases). This makes it harder to understand whether higher doses are more risky than recommended doses. The researchers also noted that the types of problems reported (pregnancy loss, birth defects, developmental issues) are the exact things that folic acid is supposed to prevent, which suggests these might be coincidences rather than caused by the supplement. The study highlights that better tracking systems are needed to collect complete information about supplements and any problems that follow

Decades of research have shown that folic acid is safe and effective at preventing serious birth defects called neural tube defects. This new study doesn’t change that conclusion. Instead, it adds to our knowledge by suggesting that while folic acid is safe at recommended doses, we should continue watching for any rare problems. The study fits with the scientific consensus that folic acid is one of the most important and safest supplements for pregnant women, but it reminds us that no medicine or supplement is 100% risk-free for every person

This study has several important limitations. First, the FDA database only includes reports that people voluntarily submit, so many problems might never be reported. Second, many reports are incomplete—researchers didn’t know the dose in 57.5% of cases. Third, just because a problem happened after taking folic acid doesn’t mean folic acid caused it. Fourth, serious cases might be more likely to be reported than minor ones, which could make problems seem more common than they really are. Finally, the study can’t tell us how many pregnant women took folic acid during this time period, so we can’t calculate the true risk

The Bottom Line

Continue taking folic acid as recommended by your doctor if you’re pregnant or planning to become pregnant. The recommended dose is 0.4 mg (400 micrograms) per day. The evidence strongly supports that folic acid prevents serious birth defects and is safe at this dose. Don’t take more than recommended without talking to your doctor. If you experience any unusual symptoms while taking folic acid, report them to your healthcare provider and the FDA’s MedWatch program. Confidence level: High for the safety of recommended doses; Moderate for the need for continued monitoring

This research matters most for pregnant women, women planning to become pregnant, and their doctors. It’s also important for health agencies that monitor supplement safety. Women who are not pregnant don’t need to be concerned about this research. If you have a history of problems during pregnancy or take higher-than-recommended doses of folic acid, talk to your doctor about whether this study applies to you

Folic acid works best when you start taking it before you become pregnant and continue through the first trimester (first three months). You should see the protective benefits against birth defects within the first few weeks of taking it regularly. If you’re already pregnant, start taking it as soon as possible. Any side effects, if they occur, would likely happen within days or weeks of starting the supplement

Want to Apply This Research?

  • Track your daily folic acid dose (in micrograms or mg) and note the date and time you take it. Also record any unusual symptoms, changes in pregnancy symptoms, or health concerns that occur within 48 hours of taking the supplement
  • Set a daily reminder to take your folic acid supplement at the same time each day (many women choose breakfast or bedtime). Use the app to log when you take it and confirm you’re taking the recommended dose of 0.4 mg per day. If your doctor recommends a different dose, update this in your app
  • Keep a monthly summary in the app showing: (1) How many days you took your folic acid as prescribed; (2) Any symptoms or concerns reported; (3) Your pregnancy milestones and checkups. Share this summary with your doctor at prenatal visits to ensure everything is going well

This research summary is for educational purposes only and should not replace medical advice from your doctor. Folic acid supplementation during pregnancy remains an important part of prenatal care and is considered safe at recommended doses. If you are pregnant, planning to become pregnant, or have concerns about folic acid supplementation, consult with your healthcare provider before making any changes to your supplement routine. If you experience any unusual symptoms while taking folic acid, contact your doctor immediately. You can also report any adverse events to the FDA’s MedWatch program at 1-888-SAFEFDA or online at fda.gov/medwatch.