Could a mother’s workplace before and during pregnancy influence child neurodevelopment? A large Danish study links several occupational categories, including transportation and defense jobs, to higher odds of autism diagnosis in children, raising new questions about toxicant exposure, stress, and prenatal health.
Study: Associations between maternal occupational history and autism spectrum disorder diagnosis in offspring in Denmark. Image credit: Veja/Shutterstock.com
A recent Occupational and Environmental Medicine study examined the relationships between maternal occupations and higher odds of autism spectrum disorder diagnosis in offspring.
Maternal occupational exposures and autism: Current evidence and research gaps
Autism spectrum disorder (ASD) is a chronic neurodevelopmental disorder characterized by impairments in social communication and the presence of restricted or repetitive behaviors. ASD prevalence shows considerable global variability, with higher rates observed in males. In Denmark, ASD prevalence increased substantially between 2004 and 2015. ASD etiology is thought to involve both genetic and environmental factors, with maternal exposures during gestation identified as key influences on neurodevelopment.
Prenatal maternal occupational exposure to toxic chemicals has been associated with atypical neurodevelopment in offspring, including elevated ASD odds related to exhaust, disinfectants, and organic solvents. Nevertheless, evidence regarding individual occupational exposures remains inconsistent, as some studies observe no associations with cleaning products, metals, solvents, or pesticides. Occupational settings frequently involve concurrent exposure to multiple toxicants and physical stressors.
Previous studies typically examined a narrow range of occupational categories and depended on self-reported or birth record data, restricting the evaluation of exposure timing during key developmental periods. Detailed analysis of maternal employment histories and exposure timing in relation to ASD diagnosis is essential, especially for occupations with modifiable chemical exposures.
Assessing maternal workplace influences on autism diagnosis
The current study used Danish registry data to assess whether maternal occupation before and during pregnancy and infancy is associated with the odds of ASD diagnosis in children born in Denmark between 1973 and 2012.
Mothers were identified from the Medical Birth Register and linked to Danish Pension Fund occupation data. Children were excluded if either parent was under 18 or over 66 at birth, or if data were missing. A total analytic sample of 110,234 participants, including 1,702 ASD cases and 108,532 controls, was included.
The Pension Fund’s detailed job histories allowed maternal occupations to be classified into 42 categories, coded as ever/never held. Job exposure was assessed at multiple time points: up to 6 months before conception, 1 year before conception, during pregnancy, and during infancy.
Occupations were grouped into seven sectors: service, transportation, goods/production, construction, public service, business/finance/hospitality, and science, technology, engineering, and mathematics (STEM). Analyses adjusted for child sex, birth year, mother’s age, parity, neuropsychiatric history, and residential location, with secondary adjustments for maternal smoking, marital status, immigration, and socioeconomic status.
The authors noted that occupational categories were used as broad proxies rather than direct measurements of toxicant exposure and did not provide detailed information on specific job tasks, measured chemical exposures, or psychosocial stress levels. In addition, maternity leave records could not fully determine whether mothers were physically present at work during all exposure windows.
Elevated ASD odds associated with specific maternal occupations
The study cohort was predominantly male, comprising 71 % of ASD cases and 70 % of controls, with the majority born in the 1990s. The average maternal age at childbirth was 29.3 years. Mothers of children with ASD more frequently had a history of neuropsychiatric disorders than those of controls.
Within goods and production sectors, maternal employment in chemical processing showed elevated ASD odds in exploratory analyses, though the association varied by exposure period and did not remain consistently significant across exposure windows and sensitivity analyses. Initial inverse associations for agriculture and construction, as well as positive associations for paper, printing, manufacturing, textiles, and clothing, did not remain significant after statistical adjustment.
In public administration, the increased ASD odds were most evident among female offspring, although this sex-specific association was attenuated after correction for multiple comparisons. Maternal employment in judicial roles was also associated with higher ASD odds, particularly during pregnancy. The overall pregnancy-window association for judicial occupations remained significant after statistical correction, although male-specific associations did not.
Judicial and military/defense occupations also showed elevated odds in the year before conception and during pregnancy. Initial findings for postal, telephone, and cleaning services, including increased odds in female offspring for cleaning services, were not statistically significant after adjustment for multiple comparisons.
After statistical correction, no significant association was observed between maternal employment in social welfare and the outcome. Defense occupations, however, consistently demonstrated increased ASD odds in both male and potentially female offspring. Maternal employment in science, technology, health, and most business fields showed no significant associations with ASD diagnosis.
Overall, maternal employment in ground transportation (aOR 1.24), public administration (aOR 1.20), and military/defense (aOR 1.59) from before conception through infancy was associated with increased ASD odds. These associations were particularly significant in male offspring for ground transportation and defense employment. However, some transportation-related findings were weakened after additional sociodemographic adjustment.
The study authors also discussed the possibility that both occupational toxicants and psychosocial stressors may contribute to neurodevelopmental outcomes through mechanisms involving inflammation, hormonal dysregulation, oxidative stress, and altered placental or fetal nervous system function, although these mechanisms were not directly measured in the study.
Conclusions
The current study highlights associations between specific maternal occupations and increased ASD odds in offspring, with evidence of sex-specific effects. Because the study was observational, the findings do not establish causation. The findings emphasize the importance of considering occupational exposures prior to conception as potentially associated factors in neurodevelopmental outcomes.
The authors also noted that some occupational associations weakened after adjustment for multiple comparisons or additional sociodemographic factors. Further research should focus on specific occupational exposures, underlying mechanisms, and phenotypic severity to better understand and mitigate these risks.
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