Table 3. Associations between Birth Spacing and Autism Spectrum Disorder Subtypes, Study to Explore Early Development (SEED), United States.

Inter-pregnancy Interval (m)	Total Sample Unadjusted OR (95% CI)	Total Sample, Adjustment for sociodemographics aOR† (95% CI)	Term Birth Sample, Adjustment for sociodemographics aOR† (95% CI)	Term Birth Sample, Adjustment for sociodemographics + maternal report of trying to get pregnant aOR† (95% CI)	Term Birth Sample, Adjustment for sociodemographics + maternal infertility disorder aOR† (95% CI)	Term Birth Sample, Adjustment for sociodemographics + prenatal hypertension, diabetes aOR† (95% CI)
ASD with ID
<18	1.4 (0.99–2.0)	1.4 (0.97–2.1)	1.6 (1.1–2.4)	1.6 (1.01–2.4)	1.5 (0.99–2.4)	1.6 (1.03–2.3)
18–59	Ref	Ref	Ref	Ref	Ref	Ref
≥60	1.9 (1.3–2.8)	1.3 (0.8–2.0)	1.4 (0.9–2.4)	1.6 (0.97–2.7)	1.6 (0.97–2.7)	1.4 (0.9–2.3)
ASD w/out ID
<18	1.2 (0.7–1.9)	1.3 (0.8–2.0)	1.4 (0.9–2.4)	1.4 (0.8–2.3)	1.4 (0.8–2.4)	1.4 (0.8–2.3)
18–59	Ref	Ref	Ref	Ref	Ref	Ref
≥60	1.6 (0.96–2.8)	1.4 (0.8–2.6)	1.5 (0.8–2.9)	1.4 (0.7–2.8)	1.5 (0.7–2.8)	1.5 (0.8–2.8)
ASD with high severity score
<18	1.7 (1.1–2.5)	1.8 (1.2–2.8)	2.0 (1.3–3.3)	2.1 (1.3–3.5)	1.9 (1.2–3.2)	2.0 (1.2–3.3)
18–59	Ref	Ref	Ref	Ref	Ref	Ref
≥60	2.1 (1.3–3.4)	1.5 (0.9–2.6)	1.8 (0.99–3.2)	1.9 (1.04–3.6)	1.9 (1.03–3.5)	1.8 (0.98–3.2)
ASD with lower severity score
<18	1.1 (0.8–1.6)	1.1 (0.7–1.6)	1.3 (0.8–1.9)	1.2 (0.8–1.8)	1.2 (0.8–1.9)	1.2 (0.8–1.9)
18–59	Ref	Ref	Ref	Ref	Ref	Ref
≥60	1.6 (1.1–2.5)	1.2 (0.7–1.9)	1.3 (0.8–2.2)	1.4 (0.8–2.4)	1.4 (0.8–2.4)	1.2 (0.7–2.1)

ASD is autism spectrum disorder case group; ID is intellectual disability.

^†aOR is adjusted odds ratio, derived from logistic regression models in which the each ASD case sub-group is compared to the POP (general population) control group. All models include adjustment for child sex, maternal age at birth, maternal education at birth, and maternal race/ethnicity. Supplemental models additionally adjusted for various potential mediator factors as indicated.