Mothers who work in occupations with high exposure to toxic chemicals more likely to have a child with autism spectrum disorder
High stress at work also linked to odds of an autism diagnosis in offspring
Association was seen for occupations held up to one year before conception
Mothers who work in jobs where they are frequently exposed to toxic chemicals or experience high stress have higher odds of having a child with autism spectrum disorder (ASD), suggest the findings of original research published online in the journal Occupational & Environmental Medicine.
ASD is a lifelong neurodevelopmental condition characterised by impaired social communication and restricted or repetitive behaviours.
Previous studies have shown potential associations between some maternal occupations and ASD in the child, but their findings are inconsistent.
However, these previous studies tended to use small study samples or relied on self-reported exposure data. They also did not evaluate the timing of occupational exposure during different developmental periods.
To overcome these limitations, the researchers of the new study examined data on mothers' occupations held before conception, during pregnancy and during infancy to investigate any impact on the neurodevelopment of any offspring.
They obtained data for 1702 cases of autism spectrum disorder (ASD) in children born between 1973 and 2012 in Denmark. These cases were matched to 108 532 controls based on sex and birth year.
The mothers' employment histories were obtained from the Danish Pension Fund Registry and grouped into seven occupational categories.
Seventy percent of the cases of ASD and the controls were male and a large proportion (46%) were born in the 1990s.
In their analysis, the researchers also took into account potential confounders including the mothers' age, history of neuropsychiatric disorders, whether they smoked during pregnancy, and socioeconomic status.
The study found the odds of having a child with ASD were increased for mothers who were employed before conception up to infancy in ground transportation, public administration and in the military.
Working in military or defence occupations before or during pregnancy increased the odds of a child being diagnosed with ASD by 59%, the study found.
Mothers who worked in ground transportation, where they may be exposed to combustion products, were at 24% greater chance of having a child with ASD.
And working in the judicial sector, before conception and during pregnancy, increased the chance of their offspring having ASD by 59%, the study found.
The associations were observed for occupations held one year before conception, during pregnancy and during infancy, although associations were weakened during the child's infancy.
The study did not find any link between ASD and the mother working in agriculture where they may have been exposed to pesticides. An increased likelihood of ASD diagnosis related to occupations such as air transportation, chemical processing industries and cleaning services was not found to be significant after taking into account other confounding factors.
The researchers suggest that working in defence occupations may mean being exposed to multiple hazards including lead from artillery handling and training exercises, exhaust fumes and industrial solvents.
Similarly, mothers employed in ground and air transportation may also be exposed to exhaust fumes and particulate matter, they theorised.
The researchers suggest that stress at work (similarly for those working in the judicial sector) may also contribute to maternal fatigue and discomfort and may adversely impact child neurodevelopment, for example, through increased inflammation during pregnancy.
This is an observational study, and as such, no firm conclusions can be drawn about cause and effect. A limitation of the study was that the occupations were based on industry categories and did not include detailed information on job titles or tasks. The study results also may not be generalisable to populations outside of Denmark.
The researchers conclude, "Maternal occupations with frequent exposure to toxicants and combustion products as well as high stress occupations could contribute to neurodevelopmental risk."
They suggest that future studies should investigate specific exposures, both alone and jointly, to investigate which have the greatest impact on the likelihood of ASD in offspring.
