A large Danish observational study has found associations between certain maternal occupations and higher odds of autism spectrum disorder in children. The findings point to possible links with toxic chemical exposure, combustion products and high work-related stress, although the researchers caution that the study cannot prove cause and effect.

Study scope

Researchers analysed data from 1,702 children with autism spectrum disorder born in Denmark between 1973 and 2012. These cases were compared with 108,532 children without an autism diagnosis, matched by sex and year of birth.

The study examined the occupations of mothers before conception, during pregnancy and in the child’s infancy, in order to assess whether workplace exposures could be associated with later neurodevelopmental outcomes.

Research institutions involved

The research team included experts from:

Johns Hopkins Bloomberg School of Public Health
Harvard T.H. Chan School of Public Health
Emory University Rollins School of Public Health
Drexel University
The Danish National Centre for Register-based Research
The Danish Cancer Society Research Centre

The study was published online in Occupational & Environmental Medicine.

Occupational data and risk factors

Information on the mothers’ employment histories came from the Danish Pension Fund Register and was classified into seven occupational categories.

The researchers also adjusted for factors that could influence the results, including maternal age, neuropsychiatric history, smoking during pregnancy and socioeconomic status.

Higher odds in specific sectors

The study found increased odds of autism spectrum disorder among children whose mothers worked, from before conception through the early years of the child’s life, in land transport, public administration and the military.

Mothers working in military or defence-related occupations before or during pregnancy had 59% higher odds of having a child later diagnosed with autism.

Those working in land transport, where exposure to combustion products may occur, had 24% higher odds.

The study also found that maternal employment in the judicial sector before conception and during pregnancy was associated with a 59% increase in the odds of autism diagnosis in children.

Possible workplace exposures

The researchers note that military occupations may involve multiple exposures, including lead from artillery handling and training, exhaust fumes and industrial solvents.

In land and air transport, possible exposures include vehicle exhaust and airborne particles.

They also suggest that high occupational stress, potentially relevant in judicial work, may contribute to maternal fatigue and physical strain. This could affect child neurodevelopment, possibly through increased inflammation during pregnancy.

No significant link in other sectors

The study did not find an association between autism and maternal work in agriculture, despite possible pesticide exposure.

No significant increase was found for occupations such as air transport, chemical processing industries and cleaning services.

Important limitations

The authors stress that this was an observational study, meaning it cannot establish a direct causal relationship.

One limitation was that occupations were classified by sector, without detailed information on exact job titles or duties. The researchers also note that the findings may not be directly generalisable to populations outside Denmark.

Source: Occupational & Environmental Medicine.

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