A diagnosis of Autism Spectrum Disorder (ASD) is more common among kids from socioeconomically disadvantaged and immigrant families, according to a new study of more than 2.3 million children in Canada.
The research comes amid an increase in autism diagnoses worldwide.
In August, a University of Otago study found the number of New Zealanders diagnosed with ASD had more than tripled over the past 15 years to reach 1.3% for children and 0.14% for adults in 2023.
The peer-reviewed study from McGill University in Montreal, published on Friday, involved 2,319,302 children born in Ontario between 2002 and 2020.
Of that number, 23,068 children (80%) received an ASD diagnosis by the age of 8, with a peak in diagnosis occurring at 4 years of age. Around two-thirds of cases (23,071 children) were boys.
According to the study, rates of ASD were highest in children from the most socioeconomically deprived, lowest-income neighbourhoods and born to immigrant mothers, and these differences worsened over time.
That was despite surveillance data from the US that, until recently, had consistently found higher ASD prevalence among White and high-income children, the report's authors said – "a pattern attributed to underdiagnosis in marginalised groups owing to financial barriers, clinician bias, and limited culturally appropriate screening".
It continued: "However, more recent data show a reversal, with higher prevalence among Black, Hispanic, and Asian or Pacific Islander children than White children. Changes in diagnostic criteria, coding practices, and surveillance methods may contribute to these shifts, illustrating how observed social disparities in ASD prevalence are shaped by evolving patterns of identification and reinforcing the need for ongoing surveillance."
The research also found children from the most socioeconomically deprived, lowest-income areas were also more likely to have been exposed to diabetes during their mother's pregnancy, as well as severe pregnancy complications and prematurity, which the authors say may have contributed to these differences.
Among all children born between 2002 and 2019, 187,487 (8.1%) were exposed to maternal diabetes; 516,379 (22.3%) were born to mothers aged 35 years or older; 48,618 (2.1%) were exposed to severe maternal morbidity; and 178,518 (7.7%) were born premature.
Maternal diabetes during pregnancy, severe maternal morbidity, and prematurity occurred more frequently in mothers residing in deprived neighbourhoods, whereas advanced maternal age occurred more often in more affluent neighbourhoods.
A higher proportion of children with ASD versus those without ASD lived in urban areas (27,813 children vs 2,116,901 children), had mothers enrolled in the Ontario Drug Benefit programme (7607 vs 413,528), and had mothers residing in the most deprived (8609 vs 516,124), lowest income (8191 vs 504,187), and most ethnically diverse (11,563 children vs 767,983) neighbourhoods.
A higher proportion of children with ASD were born to immigrant mothers compared with children without ASD (9171 vs 626,753), particularly among children whose mothers originated from low- and middle-income regions, including Sub-Saharan Africa, East Asia and the Pacific, and the Middle East and North Africa.
The Ontario Drug Benefit programme covers the cost of more than 5900 designated prescription medications and about 1500 additional drugs for eligible residents.
The authors concluded the study had found a "growing cumulative incidence of ASD diagnoses among children born to socioeconomically disadvantaged and immigrant mothers, indicating a changing profile of children with ASD".
"The increase was particularly pronounced among children of immigrant mothers from low- and middle-income countries, suggesting that immigration-related factors may contribute to these trends."
However, they also noted socioeconomic disparities had been observed among children of Canadian-born mothers, indicating that "immigration alone does not explain the widening differences in ASD diagnosis".
"The fact that these social patterns of ASD diagnosis emerged within a public health care system point to the influence of non-access-related factors.
"The parallel increase in diabetes during pregnancy across socioeconomic and immigration strata, mirroring patterns observed for ASD, raises the possibility that diabetes may contribute to these disparities.
"However, other prenatal risk factors for ASD did not demonstrate similar trends, underscoring that the drivers of these disparities are likely complex and multifactorial.
"Further research is needed to disentangle true differences in risk from variations in service availability."
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