Obstetrician Jeanne Conry has long paid attention to the “1,300-day window”— the months before conception through a child’s second birthday. Studies show nutrition and lifestyle during this period can shape pregnancy outcomes and the long-term health of the babies. Conry began to wonder if such factors could also influence autism.
She is now helping lead an educational push aimed at alerting women to their exposure to toxins, stress and infections during this narrow and consequential window — guided by the idea that what happens then may subtly shape eggs or sperm, and in turn, influence a child’s development long before pregnancy begins.
“The more we research, the more we see links between different chemical exposures and autism so if we reduce those links we will ideally reduce cases,” Conry said.
For years, movements like this existed on the fringes. But recent studies are giving it new weight, raising a provocative question that was once almost taboo: could some cases of autism actually be preventable?
One peer-reviewed paper generating buzz in the autism research community published in December argues that a staggering number, more than half of autism cases, could be prevented with the right interventions. It proposes a “three-hit” theory suggesting that genetic susceptibility combined with environmental exposure and prolonged period of physiological stress contribute to autism.
Separately, two recent studies found that parents with the highest levels of an unusual sensitivity to everyday substances even at low levels, as measured by self-reported symptom patterns and validated questionnaires, were two times to 5.7 times more likely to report having a child with autism, prompting researchers to urge couples trying to conceive to minimize environmental exposures in their homes.
Both lines of research rest more on hypothesis than on settled evidence; the science linking environmental exposures to autism remains preliminary, defined by suggestive correlations rather than demonstrable causation.
Still, the ideas are helping fuel a broader cultural focus on preconception health.
On Instagram and TikTok, a growing number of wellness influencers have embraced what they call “trimester zero,” advising women — often mixing science-backed guidance with largely unproven claims — to stop wearing nail polish, take specific supplements, meditate and work to lower cortisol levels before conceiving. Books with titles like the “The Fertility Formula,” “The Preconception Revolution” and “9 Months is Not Enough” promote the idea that women are more in control of the health of their fetuses than they might think.
The new interest in the preconception period comes amid renewed national attention to environmental explanations for autism. Health and Human Services Secretary Robert F. Kennedy Jr. has drawn widespread criticism for claiming that an environmental toxin is responsible for rising autism rates and for describing the condition as a “preventable disease.” Many autism researchers disputed those assertions, arguing that increases in prevalence are more plausibly explained by expanded diagnostic criteria and greater awareness — and that autism is not a disease at all, but a form of human diversity.
The idea of prevention does not merely promise scientific clarity; it also assigns responsibility. If autism is shaped not only by biology but by environmental conditions that governments and institutions can influence, uncomfortable ethical questions inevitably follow.
David Beversdorf, a University of Missouri professor who studies autism and stress, supports the major medical societies’ recommendation that OB/GYNs counsel patients on diet and fitness before conception. But he is wary of extending that routine guidance to broad warnings about environmental exposures, citing limited evidence and the risk of impractical — or counterproductive — advice.
“We don’t have the evidence yet to say what you need to do, that pushes the advice into ‘scare’ things,” he said. “I’d be nervous going that far.”
1,300 days
The roughly three years spanning the months before conception, pregnancy and early infancy are a uniquely sensitive period in human development — one that can change a person’s lifetime health trajectory. Research, much of it funded by the National Institutes of Health, has linked habits and exposures during this period to obesity, asthma, childhood cancers, decreased intelligence and working memory, and numerous other issues.
One of the studies that has drawn a lot of attention recently is by Robert Naviaux, a researcher at the University of California at San Diego known for his work with mitochondria, the cell’s powerhouses. Naviaux and his team argue for a reframing of how autism is thought of: instead of almost fixed genetic condition they suggest it may be better understood as a metabolic and inflammatory syndrome shaped by both biology and environment.
At the center of his theory is the cell danger response, a temporary survival state triggered by perceived threat.
When activated, mitochondria shift from supporting growth to signaling distress, slowing development to allow for repair. Problems arise, Naviaux and his colleagues say, when this response fails to shut off.
In a three-hit model, autism risk emerges when genetic vulnerability meets an early environmental trigger, followed by prolonged activation of the danger response during critical periods of brain development. The stressor might be a viral infection or inflammation due to air pollution. From this view, autism reflects development under chronic biological stress — a brain adapting to a world that, at a cellular level, never quite feels safe.
Naviaux believes that figuring out who might be more susceptible to autism — perhaps by analyzing genetic variants, metabolic biomarkers, brain scans and early environmental exposures — could open a window for intervention, allowing clinicians to make targeted changes before autism fully emerges.
He often draws a parallel to phenylketonuria, or PKU, a rare metabolic disorder in which the body cannot break down a particular amino acid, leading to seizures, intellectual disability and other serious complications. Before its cause was understood, PKU was considered untreatable. Today, however, it is routinely managed through early detection, a strict low-protein diet, specialized medical formulas, and, in some cases, medication. “PKU is the reason universal newborn screening exists,” Naviaux noted.
The lesson, he argues, is not that all children are at risk, but that some are more sensitive than others.
“The key is early identification,” he said. “There is a subset of children who may be especially responsive to changes in their environment.”
Chemical intolerance
A related theory of how autism can develop starts with the parents.
Claudia S. Miller, professor emeritus in the Department of Family and Community Medicine at University of Texas Health at San Antonio, has theorized that autism may in some cases be linked to a significant chemical exposure experienced by one or both parents — such as toxic mold — that leads to a chronic condition known as chemical intolerance. People with chemical intolerance — which scientists believe may be due to immune signaling, neuroinflammation, metabolic stress, nervous system sensitization or a combination of the above — can develop severe symptoms, including headaches, fatigue and confusion, when exposed to everyday substances like household cleaners, reactions that most people do not experience.
Miller suggests that chemical intolerance involves mast cells, which serve as first responders in the immune system. When triggered by chemicals or viruses, these cells release inflammatory molecules that produce allergy-like reactions. She theorizes that this inflammatory response could, in turn, disrupt typical brain development and lead to autism.
In 2024, Miller and her colleagues published an analysis showing that in a group of nearly 8,000 U.S. adults, parents with chemical intolerance scores in the top 10th percentile were 5.7 times as likely to have a child with autism when compared with those in the bottom 10th percentile.
Those findings were replicated in a study published in January 2026 in the Journal of Xenobiotics, which examined children in five countries. In Italy, India and the United States, children born to parents with the highest levels of chemical intolerance had more than a twofold increased risk of autism; in Mexico, the risk was 1.9 times higher. No association was found in the Japanese data, though researchers suggested cultural differences in diagnosis and awareness may have influenced the results.
Neither study establishes causation, but she said that both raise enough questions about a possible link that in recent years Miller has worked alongside physicians to encourage screening of expectant parents for chemical intolerance and to offer environmental counseling when appropriate. She notes that with tens of thousands of synthetic chemicals present in everyday products — many introduced during the surge of industrialization after World War II — the number of potential triggers is vast.
“Our world is totally different than when our grandparents were younger,” she said.
‘Aha’ moments
Conry is a physician outside of Sacramento who heads the International Federation of Gynecology and Obstetrics of which the American College of Obstetricians and Gynecologists, one of the country’s most influential medical societies, is a member.
She recounts that she’s had several “aha” moments in her career when it comes to environmental exposures and pregnancy — after learning about lead-contaminated lipstick and serious birth defects in babies born to women who live in farming communities — and has dedicated the past few years to convening seminars, speaking at trainings and other events to educate doctors and patients about how to minimize toxic exposures.
Conry believes assessing exposures at home, work and the community should be a routine part of a fertility consult.
She said the idea is not that parents can — or should — engineer perfect outcomes, but that small changes made early may shift probabilities at the margins.
Helen Tager-Flusberg, director of Boston University’s Center for Autism Research Excellence and a founder of a coalition of autism scientists calling for more rigorous research, said there is little evidence that specific interventions during the preconception window could make a significant difference. She cautioned that focusing on this period is premature — and possibly harmful — given the current limits of the science. She pointed to the past, when both researchers and the public wrongly blamed so-called “refrigerator mothers” (who were cold or emotionally distant) and their parenting for autism.
“For decades now we’ve done too much as a society to make women feel the burden is on them,” she said.
She said the best advice for women considering pregnancy hasn’t changed for decades: take prenatal vitamins with folic acid, eat a healthy diet, stay fit, and avoid drugs, alcohol and smoking.
Tager-Flusberg said there is stronger evidence for other autism risk factors — one being several high-impact genes that put some kids at risk for a more severe form of the condition. Should women be allowed to screen for them in the womb? She said the links between parental age and autism are far stronger than those found for exposures such as BPA, phthalates and other environmental factors. In theory, the medical community could advise women to have children in their 20s and men before their late 30s or early 40s to reduce autism rates. But she noted that such guidance raises broader societal concerns about reproductive autonomy, gender equality, economic realities as well as a risk of stigmatizing older parents.
“These are new territories,” she said, “and we are not ready as a society to be thinking about them.”
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