New studies clarify how maternal immune activation during pregnancy may relate to autism likelihood

A growing body of research is refining our understanding of how immune system activity during pregnancy may relate to the likelihood of a child later being diagnosed with autism. Three new studies in Nature and JAMA, alongside systematic reviews, converge on maternal immune activation (MIA) as one of the most replicable environmental factors associated with autism — while also revealing nuances about timing, biological mechanisms, and interactions with pollution. It's important to note that these are small increases in likelihood, and most children exposed to these factors will not be autistic.

The immune-autism link strengthens A January 2026 Nature study analyzing over 15,000 birth records found that maternal infections requiring hospitalization during pregnancy were associated with 32% higher odds of an autism diagnosis, though absolute risk remained low. This aligns with a December 2025 primate study in Molecular Psychiatry showing that induced immune activation causes lasting changes in amygdala gene expression in offspring. Meanwhile, a pilot twin study in Nature found distinct cytokine profiles (cytokines are immune system proteins that help regulate inflammation) in mothers whose twins later had autism.

A March 2022 Simons Foundation analysis found maternal COVID-19 infection was associated with increased inflammatory markers also seen in other MIA-autism studies.

Pollution interacts with immune factors Prenatal exposure to fine particulate air pollution (PM2.5) independently correlated with autism likelihood in a October 2025 JAMA Network Open study, with nitrate and metal components showing strongest links. A 2023 review in Environment International noted these pollutants may exacerbate maternal immune responses, though other factors like urban living may also play a role.

COVID-19 research is emerging Research is ongoing to understand the potential impact of COVID-19 infection during pregnancy, but current evidence suggests the overall risk remains low. A March 2022 Simons Foundation analysis found maternal COVID-19 infection was associated with increased inflammatory markers also seen in other MIA-autism studies.

What's happening biologically? The primate study revealed that maternal immune activation triggers persistent dysregulation in genes related to synaptic function and immune signaling in the offspring's amygdala — a brain region involved in social-emotional processing. This suggests immune factors may alter neurodevelopment at the molecular level, though how this translates to human behavior requires further study. Genetic factors likely interact with these environmental influences, as autism is known to have strong hereditary components.