Mothers who work in occupations involving frequent exposure to toxic chemicals or high levels of stress have an increased likelihood of having a child diagnosed with autism spectrum disorder, according to a new study published online in the journal Occupational & Environmental Medicine.
The research team, drawing from Johns Hopkins Bloomberg School of Public Health, Harvard T.H. Chan School of Public Health, Emory University’s Rollins School of Public Health, Drexel University, Denmark’s National Centre for Register-based Research, and the Danish Cancer Society’s Institute of Cancer Epidemiology, analyzed mothers’ occupational histories before conception, during pregnancy, and during infancy to explore potential effects on the neurodevelopmental outcomes of their children.
The study examined data on 1,702 children born in Denmark between 1973 and 2012 who had received an autism spectrum disorder diagnosis. These cases were compared against 108,532 children without an autism diagnosis, matched by sex and year of birth. The mothers’ employment histories were drawn from the Danish Pension Fund Registry and classified into seven occupational categories. The analysis also accounted for potential confounding factors including maternal age, history of neuropsychiatric disorders, smoking during pregnancy, and socioeconomic status.
The Findings
The study found elevated odds of having a child with autism among mothers who worked, from before conception through the child’s early years, in land transportation, public administration, and the military.
Working in military or defense occupations before or during pregnancy was associated with a 59% higher likelihood of an autism diagnosis in the child. Mothers employed in land transportation, where exposure to combustion byproducts is common, had a 24% higher likelihood of having a child with autism. Working in the justice sector before conception and during pregnancy was also associated with a 59% increased likelihood of autism in the child.
These associations were observed across all three windows examined, namely before conception, during pregnancy, and during infancy, though they weakened during the infant period.
What Did Not Show a Connection
Notably, the study found no significant association between autism and maternal employment in agriculture, despite the potential for pesticide exposure in that sector. Similarly, no meaningful increase was found for occupations in air transportation, chemical processing industries, or cleaning services.
How Researchers Interpret the Results
The researchers suggest that military occupations may involve exposure to multiple hazards, including lead from firearms training and shooting exercises, vehicle exhaust, and industrial solvents. Mothers working in land and air transportation may similarly be exposed to exhaust fumes and airborne particulate matter.
On the stress side, the researchers note that high occupational stress, as may be the case in the justice sector, can contribute to maternal fatigue and physical strain, potentially affecting fetal neurodevelopment through elevated inflammatory processes during pregnancy.
The study’s authors are careful to note that this is an observational study, meaning no firm conclusions about cause and effect can be drawn. One limitation is that occupations were categorized by sector rather than specific job title or duties, which may obscure important variation within categories. The findings may also not be generalizable to populations outside Denmark.
