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Significance Rates of autism diagnosis in the United States have historically been higher among more advantaged social groups—Whites and those of higher socioeconomic status (SES). Using data from all births in the state of California in 1992 through 2016, we find that these trends reversed during our study period. By 2018, diagnosed autism incidence rates for 3- to 6-y-old children were higher for children of Black and Asian mothers than children of non-Hispanic White mothers and were higher for children of lower SES than of higher SES parents. These reversals point to the fundamental role that access to knowledge and resources plays in driving increased autism prevalence and shifting patterns of autism cases over the past quarter-century., As rates of autism diagnosis increased dramatically over the past number of decades, prevalence rates were generally highest among Whites and among those of higher socioeconomic status (SES). Using a unique, population-level dataset, we find that rates of autism diagnosis continued to be on the rise in recent years, but who is diagnosed changed during the study period. Our data consist of birth records of all 13,272,573 children born in the state of California in 1992 through 2016 linked to autism caseload records for January 1992 through November 2019 from California’s Department of Developmental Services. California’s diagnosed autism incidence rate rose from 0.49 per 1,000 3–6 y olds in 1998 to 3.49 per 1,000 3–6 y olds in 2018, a 612% increase. However, diagnosed incidence rates did not rise uniformly across sociodemographic groups. By 2018, children of Black and Asian mothers were diagnosed at higher rates than children of non-Hispanic White mothers. Furthermore, among children of non-Hispanic White and Asian mothers, children of lower SES were diagnosed at higher rates than children of higher SES. These changes align with sociological theories of health disparities and contain important clues for more fully understanding the autism epidemic.

Previous studies report associations between conception with assisted reproductive technology (ART) and autism. Whether these associations reflect an ascertainment or biologic effect is undetermined. We assessed diagnosis age and initial autism symptom severity among >30,000 children with autism from a linkage study of California Department of Developmental Services records, birth records, and the National ART Surveillance System. Median diagnosis age and symptom severity levels were significantly lower for ART-conceived than non-ART-conceived children. After adjustment for differences in the socio-demographic profiles of the two groups, the diagnosis age differentials were greatly attenuated and there were no differences in autism symptomatology. Thus, ascertainment issues related to SES, not ART per se, are likely the driving influence of the differences we initially observed.

Sir, We appreciate the interest of Dr Barad et al. in our analysis of the association of assisted reproductive technology (ART) treatment and parental infertility diagnosis with autism in ART-conceived children (Kissin et al., 2015). Dr Barad et al. express concern that the analysis was not adjusted ‘for race/ethnicity and/or socioeconomic status.’ We did consider both maternal race/ethnicity and education (the latter as a proxy for socioeconomic status) among other characteristics for inclusion in models that explored the association of autism with ART treatment factors and parental infertility diagnosis. Neither factor was significant in the univariable analysis and, therefore, was not included in in the models. However, in response to Dr Barad et al.’s suggestion, we refit the models with addition of these two factors. As expected, the risk estimates for the association of ICSI with autism diagnosis remained statistically significant for both singletons [adjusted hazard risk ratio, aHRR 1.73 (1.11–2.69)] and multiples [aHRR 1.51 (1.06–2.15)]. Contrary to Dr Barad et al.’s surmise that socioeconomically advantaged patients would utilize ICSI to a higher degree, there was no evidence that utilization of ICSI was significantly associated with either race/ethnicity (70% of ART users with ICSI were non-Hispanic white, compared with 70% of ART users without ICSI) or socioeconomic status (89% of ICSI users were college graduates, compared with 87% of women who used ART without ICSI). The dramatic increase in use of ICSI during the study period without similar increase in autism diagnosis in ART-conceived children can likely be explained by the relatively low prevalence of autism. Using a mathematical assessment model for estimating the effects of changes in the prevalence of individual risk factors on autism prevalence (Schieve et al., 2011), we estimate that the 82% increase of ICSI use would be expected to result in a 14.4% increase in autism among singletons, and thus a prevalence increase from0.9 to 1.03%. Likewise, the ICSI use increase we observed would be expected to result in a 15.5% autism increase among multiples, which translates to a prevalence increase from 1.2 to 1.39% among multiples. Such small increases in autism prevalence are difficult to detect with any precision. Moreover, while increasing ICSI utilization may have led to a slight increase in autism prevalence, other factors, such as the decline in multiple births among ART deliveries, might have affected the trend in the opposite direction. As we clearly noted in our article, an underlying biological mechanism through which ICSI could be associated with autism is not known and may be related to the procedure itself, characteristics of the patients selected for the procedure, or other factors. However the possibility of risk and the lack of convincing evidence of benefit do not appear to favor use of ICSI without male-factor infertility diagnosis (ASRM, 2012).

Objectives. We assessed the association between assisted reproductive technology (ART) and diagnosed autistic disorder in a population-based sample of California births. Methods. We performed an observational cohort study using linked records from the California Birth Master Files for 1997 through 2007, the California Department of Developmental Services autism caseload for 1997 through 2011, and the Centers for Disease Control and Prevention’s National ART Surveillance System for live births in 1997 through 2007. Participants were all 5 926 251 live births, including 48 865 ART-originated infants and 32 922 cases of autism diagnosed by the Department of Developmental Services. We compared births originated using ART with births originated without ART for incidence of autism. Results. In the full population, the incidence of diagnosed autism was twice as high for ART as non-ART births. The association was diminished by excluding mothers unlikely to use ART; adjustment for demographic and adverse prenatal and perinatal outcomes reduced the association substantially, although statistical significance persisted for mothers aged 20 to 34 years. Conclusions. The association between ART and autism is primarily explained by adverse prenatal and perinatal outcomes and multiple births.

The incidence and prevalence of autism have dramatically increased over the last 20 years. Decomposition of autism incidence rates into age, period and cohort effects disentangle underlying domains of causal factors linked to time trends. We estimate an age-period-cohort effect model for autism diagnostic incidence overall and by level of functioning.Data are drawn from sequential cohorts of all 6 501 262 individuals born in California from 1992 to 2003. Autism diagnoses from 1994 to 2005 were ascertained from the California Department of Development Services Client Development and Evaluation Report.Compared with those born in 1992, each successively younger cohort has significantly higher odds of an autism diagnosis than the previous cohort, controlling for age and period effects. For example, individuals born in 2003 have 16.6 times the odds of an autism diagnosis compared with those born in 1992 [95% confidence interval (CI) 7.8-35.3]. The cohort effect observed in these data is stronger for high than for low-functioning children with an autism diagnosis.Autism incidence in California exhibits a robust and linear positive cohort effect that is stronger among high-functioning children with an autism diagnosis. This finding indicates that the primary drivers of the increases in autism diagnoses must be factors that: (i) have increased linearly year-to-year; (ii) aggregate in birth cohorts; and (iii) are stronger among children with higher levels of functioning.

Background The incidence of autism rose dramatically between 1992 and 2001, while the age at which children were first diagnosed declined. During this period the size and composition of the autism caseload has changed, but little is known about whether the factors associated with the timing of diagnosis may also have shifted. Using a multilevel analysis strategy, the individual and community-level factors associated with age of diagnosis were modelled across 10 birth cohorts of California children. Methods Linked birth and administrative records on 17185 children with diagnoses of autistic disorder born in California between 1992 and 2001 and enrolled with the California Department of Developmental Services (DDS) were analysed. Information on cases, their parents and their residential location were extracted from birth and DDS records. Zip codes of residence were matched to census data to create community-level measures. Multilevel linear models were estimated for each birth cohort, with individual-level effects for sex, race, parental characteristics, poverty status, birth order and symptom expression. At the community level measures of educational and economic composition, local autism prevalence and the presence of a child psychiatrist were included. Results Children with highly educated parents are diagnosed earlier, and this effect has strengthened over time. There is a persistent gap in the age of diagnosis between high and low socioeconomic status (SES) children that has shrunk but not disappeared over time. Conclusion Routine screening for autism in early childhood for all children, particularly those of low SES, is necessary to eliminate disparities in early intervention.

Objectives. We sought to estimate the risk for autism associated with maternal and paternal age across successive birth cohorts. Methods. We linked birth records and autism diagnostic records from the California Department of Developmental Services for children born in California between 1992 and 2000 to calculate the risk associated with maternal and paternal age for each birth cohort as well as for the pooled data. Results. The categorical risks associated with maternal age over 40 years ranged from a high of 1.84 (95% confidence interval [CI] = 1.37, 2.47) to a low of 1.27 (95% CI = 0.95, 1.69). The risk associated with paternal age ranged from 1.29 (95% CI = 1.03, 1.6) to 1.71 (95% CI = 1.41, 2.08). Conclusions. Pooling data across multiple birth cohorts inflates the risk associated with paternal age. Analyses that do not suffer from problems produced by pooling across birth cohorts demonstrated that advanced maternal age, rather than paternal age, may pose greater risk. Future research examining parental age as a risk factor must be careful to avoid the paradoxes that can arise from pooling data, particularly during periods of social demographic change.