Can a mother’s workplace before and during pregnancy influence her child’s neurodevelopment? A large Danish study has linked several occupational categories, including transport and defense jobs, to higher odds of autism diagnosis in children, raising new questions about toxic exposure, stress and prenatal health.
Study: Association between maternal occupational history and offspring autism spectrum disorder diagnosis in Denmark. Image credit: Veja/Shutterstock.com
recent industrial and environmental medicine A study investigating the relationship between mother’s occupation and high probability of autism spectrum disorder Diagnosis of offspring.
Maternal occupational exposure 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. There is considerable variation in the prevalence of ASD worldwide, with higher rates observed in men. In Denmark, ASD prevalence increased significantly between 2004 and 2015. Both genetic and environmental factors are thought to be involved in the pathogenesis of ASD, and maternal exposure during pregnancy has been identified as an important influence on neurodevelopment.
Prenatal maternal occupational exposure to toxic chemicals is associated with atypical neurodevelopment in offspring, including increased odds of ASD associated with exhaust fumes, disinfectants, and organic solvents. Nevertheless, evidence regarding occupational exposure in individuals remains inconsistent, as some studies have not observed associations with cleaning agents, metals, solvents, or pesticides. Occupational environments often involve simultaneous exposure to multiple toxic substances and physical stressors.
Previous studies have typically examined a narrow range of occupational categories and relied on self-report or birth record data, limiting assessment of the timing of exposure during critical developmental periods. A detailed analysis of maternal occupational history and exposure timing in relation to ASD diagnosis is essential, especially for occupations with modifiable chemical exposures.
Assessing the influence of mothers’ workplaces on autism diagnosis
The current study utilized Danish registry data to assess whether maternal occupation before and during pregnancy and infancy was associated with the probability of ASD diagnosis in children born in Denmark between 1973 and 2012.
Mothers were identified from the medical birth register and linked to occupational data from the Danish Pension Fund. Children were excluded if either parent was younger than 18 years or older than 66 years at birth, or if data were missing. A total analytic sample of 110,234 participants was included, including 1,702 ASD cases and 108,532 controls.
The pension fund’s detailed work history classified mothers’ occupations into 42 categories, allowing them to be coded as ever/never worked. Work exposure was assessed at multiple time points up to 6 months before pregnancy, 1 year before pregnancy, during pregnancy, and in infancy.
Occupations were grouped into seven sectors: services, transportation, goods/production, construction, public services, business/finance/hospitality, and science, technology, engineering, and mathematics (STEM). Analyzes adjusted for child sex, year of birth, maternal age, parity, neuropsychiatric history, and place of residence, with quadratic adjustments for maternal smoking, marital status, immigration, and socioeconomic status.
The authors noted that occupational categories were used as a broad proxy rather than a direct measure of toxic exposure and did not provide detailed information about specific job duties, measured chemical exposures, or psychosocial stress levels. Additionally, maternity leave records did not allow us to fully determine whether mothers were physically present at work during all exposure periods.
Increased odds of ASD associated with specific maternal occupations
Study subjects were primarily male, comprising 71% of ASD cases and 70% of controls, and the majority were born in the 1990s. The average age of mothers at delivery was 29.3 years. Mothers of children with ASD were more likely to have a history of neuropsychiatric disorders than mothers in the control group.
Within the products and production sector, maternal employment in chemical processing showed increased odds of ASD in exploratory analyses, but the association varied by exposure duration and did not remain consistently significant across exposure windows and sensitivity analyses. The initial inverse associations for agriculture and construction and positive associations for paper, printing, manufacturing, textiles, and clothing did not remain significant after statistical adjustment.
Administratively, the increase in ASD odds was most pronounced among girls, but this sex-specific association was attenuated after adjustment for multiple comparisons. Maternal employment in a judicial role was also associated with increased odds of ASD, particularly during pregnancy. Although the association of judicial service with overall gestational age remained significant after statistical adjustment, the male-specific association did not.
Justice and military/defense occupations also showed higher odds in the year before and during pregnancy. Initial findings regarding mail, telephone, and cleaning services, including increased odds of female offspring receiving cleaning services, were not statistically significant after adjustment for multiple comparisons.
After statistical adjustment, no significant association was observed between maternal employment in social work and outcomes. However, defense employment has been consistently shown to increase the odds of ASD in both male and potentially female offspring. Maternal employment in science, technology, health, and most business fields showed no significant association with ASD diagnosis.
Overall, maternal ground transportation (aOR 1.24), government (aOR 1.20), and military/defense (aOR 1.59) employment from preconception to infancy was associated with increased odds of ASD. These associations were particularly pronounced among male offspring of land transport and defense occupations. However, additional sociodemographic adjustments attenuated some of the transport-related findings.
The study authors also discussed the possibility that both occupational toxicants and psychosocial stressors contribute to neurodevelopmental outcomes through mechanisms including inflammation, hormonal dysregulation, oxidative stress, and changes in placental or fetal nervous system function, although these mechanisms were not directly measured in the study.
conclusion
The current study highlights the association between certain maternal occupations and increased odds of ASD in children, with evidence of gender-specific effects. Because this study is observational, the results do not prove causation. The results of this study highlight the importance of considering preconception occupational exposures as a factor potentially associated with neurodevelopmental outcomes.
The authors also noted that some occupational associations weakened after adjusting for multiple comparisons and 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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