What Can a Pregnant Woman Do to Prevent Autism? The Honest Answer.

The honest answer is shorter, and stranger, than the headlines suggest — and the one thing that actually has data is the thing no one in Washington is talking about.

A pregnant patient asked me how to keep her baby from being autistic. The honest answer is shorter, and stranger, than the headlines suggest — and the one thing that actually has data is the thing no one in Washington is talking about.

A patient asked me last month how she could keep her baby from being autistic. She had read the headlines. She was scared. She deserved a straight answer, so here it is.

First, what autism is. Autism spectrum disorder is a difference in how the brain develops. It shapes how a person communicates, connects with others, and takes in the world. It is not a disease caught during pregnancy. It is not an injury. It is a wide spectrum. Some autistic people need lifelong support. Others live fully independent lives and would not trade the way their minds work.

The numbers have climbed fast. In 2000, about 1 in 150 American children were identified with autism by age 8. By 2016 it was 1 in 54. The newest count from the CDC is 1 in 31. That looks like an epidemic. Most of it is not.

Much of the rise comes from better counting. The definition of autism widened over the years. Awareness grew. Doctors began screening earlier and catching milder cases they once missed. Children who used to be labeled something else, or nothing at all, now get a diagnosis. The sharpest recent increases are among Black, Hispanic, and Asian children and in poorer neighborhoods, exactly the groups who were underdiagnosed for decades. That is not a toxin spreading through the population. That is a system finally looking.

So is it the environment? The food? A shot? A pill? This is where the evidence gets clear, and where it collides with the headlines.

Autism is mostly genetic. Studies of twins and of large families all point the same way: somewhere between 60 and 90 percent of the risk is inherited. When one identical twin is autistic, the other very often is too. This is the single most important fact about autism, and the one most likely to be left out of a news segment. For most families, the odds are set in part before the pregnancy even begins. That is not a mother’s fault, and it is not something a diet can undo.

In September 2025, the White House announced that acetaminophen, the drug in Tylenol, taken during pregnancy could cause autism, and urged women to avoid it. The science does not support that claim. The largest and best study followed nearly 2.5 million children in Sweden. Researchers compared siblings: the same mother, the same genes, one pregnancy with acetaminophen and one without. The autism rates were the same. The earlier studies that found a link had not accounted for the reasons a mother takes the drug in the first place, such as fever, pain, and infection, which run in families along with the genes. Acetaminophen remains the safest choice for fever and pain in pregnancy, and every major obstetric society said so within hours.

Here is the part that worries me more. A high fever in pregnancy is itself linked to autism. In one large study, a fever in the second trimester raised the odds by about 40 percent, and three or more fevers after the twelfth week tripled them. Telling a pregnant woman to tough out a fever instead of treating it gets the risk exactly backward.

So what can a woman actually do? Less than the headlines promise, but not nothing.

The one step with real evidence behind it is folic acid, and the timing is everything. In a study of more than 85,000 Norwegian children, women who took folic acid from about four weeks before conception through the first weeks of pregnancy had roughly 40 percent lower odds of autistic disorder, about 1 in 1,000 instead of 2 in 1,000. The protection showed up only when the supplement started before the pregnancy test turned positive. This is the same vitamin already recommended to prevent spina bifida, a birth defect of the spine, which is why I tell every patient planning a pregnancy to start it early.

A few other things shift the odds a little. Treating fevers and infections rather than ignoring them. Reaching a healthy weight and getting blood sugar under control before pregnancy, since obesity and diabetes each raise the risk. Avoiding the seizure medicine valproate when another option exists, because it is one of the few exposures with a clear causal link to autism. Not smoking. None of these are magic. They move a small amount of risk that sits on top of a baseline that is mostly genetic.

And the things being sold as prevention or cure, such as skipping vaccines, avoiding Tylenol, or the drug leucovorin, do not prevent autism. They pull attention away from the one supplement that has data.

My take. The question itself does a quiet harm. It tells mothers that autism is a mistake they can avoid if only they are careful enough, and that is false. Autism is overwhelmingly genetic, the rise is mostly better detection, and the prenatal choices that move the needle are few and modest. Take folic acid before you conceive. Treat your fevers. Get healthy before pregnancy if you can. Then live your life without the guilt the headlines are selling. The loudest voices on autism prevention right now are pointing at a pill that does nothing while ignoring the vitamin that does something. That tells you who is reading the evidence and who is reading the room.

Bottom line: if you are planning a pregnancy, start folic acid now and treat fevers when they come. Most of what the headlines are shouting about is noise. ObGyn Intelligence is free because the work matters. If you want to support it, a paid subscription keeps it independent.

References

1. Shaw KA, Williams S, Patrick ME, et al. Prevalence and early identification of autism spectrum disorder among children aged 4 and 8 years — Autism and Developmental Disabilities Monitoring Network, 16 sites, United States, 2022. MMWR Surveill Summ. 2025;74(SS-2):1-22. doi:10.15585/mmwr.ss7402a1.

2. Tick B, Bolton P, Happé F, Rutter M, Rijsdijk F. Heritability of autism spectrum disorders: a meta-analysis of twin studies. J Child Psychol Psychiatry. 2016;57(5):585-595. doi:10.1111/jcpp.12499. PMID 26709141.

3. Surén P, Roth C, Bresnahan M, et al. Association between maternal use of folic acid supplements and risk of autism spectrum disorders in children. JAMA. 2013;309(6):570-577. doi:10.1001/jama.2012.155925. PMID 23403681.

4. Ahlqvist VH, Sjöqvist H, Dalman C, et al. Acetaminophen use during pregnancy and children’s risk of autism, ADHD, and intellectual disability. JAMA. 2024;331(14):1205-1214. doi:10.1001/jama.2024.3172. PMID 38592388.

5. Hornig M, Bresnahan MA, Che X, et al. Prenatal fever and autism risk. Mol Psychiatry. 2018;23(3):759-766. doi:10.1038/mp.2017.119. PMID 28607458.

6. Hernández-Díaz S, Straub L, Bateman BT, et al. Risk of autism after prenatal topiramate, valproate, or lamotrigine exposure. N Engl J Med. 2024;390(12):1069-1079. doi:10.1056/NEJMoa2309359. PMID 38507750.

7. American College of Obstetricians and Gynecologists. Acetaminophen use in pregnancy and neurodevelopmental outcomes. Practice Advisory. Washington, DC: ACOG; September 2025.