Study population

The study population was a subset of a parent study on the association between polyunsaturated fatty acids and ASD (Lyall et al., 2021). Participants for this study were drawn from children born in 2011–2012 whose mothers had serum banked through participation in California’s Prenatal Screening (PNS) Program. The PNS Program offers blood screening tests to all pregnant women between 15 and 20 weeks gestation in order to detect certain congenital abnormalities (Cunningham & Tompkinson, 1999). The California Biobank Program banks PNS specimens from women residing in Fresno, Madera, Kings, Tulare, Kern, Orange, and San Diego counties. ASD cases were identified through the California Department of Developmental Services (DDS), which provides support services to Californian children with developmental disabilities. DDS serves an estimated 75–80% of Californian children with ASD, encompassing the more severe cases (Croen et al., 2002). Children were defined as cases if they had a DDS record of provided services for ASD at the time of data linkage (February 2017, mean child age at linkage: 5.24 years). Diagnosis of ASD within DDS has been previously validated (Windham et al., 2011). Controls were selected from birth certificate data of children who did not link to DDS client data. California birth certificate data was linked to data from DDS and PNS Program records after excluding infant deaths. Covariate data was obtained primarily from birth records, as well as PNS records. From these linked data sets, 500 cases were randomly selected and frequency matched to 501 controls on birth year, birth month, and sex. Only singleton births were sampled. As four serum samples were unable to be analyzed, the final study sample included 498 cases and 499 controls.