Table 1:

Comparison of covariate distributions among cases with autism and matched controls

	Cases (N=778)		Controls (N=778)
Covariate	N	%	N	%	P-value1
Birth year					1.0
1987–1990	68	8.7	68	8.7
1991–1993	209	26.9	209	26.9
1994–1996	208	26.7	208	26.7
1997–2005	293	37.7	293	37.7
Infant sex					1.0
Male	606	77.9	606	77.9
Female	172	22.1	172	22.1
Maternal age					0.01
≤19	9	1.2	21	2.7
20–24	107	13.8	134	17.2
25–29	257	33.0	254	32.7
30–34	228	29.3	233	30.0
35–39	141	18.1	116	14.9
≥40	36	4.6	20	2.6
Maternal parity3					0.001
0	189	24.3	254	32.9
1	266	34.2	241	31.2
2	177	22.8	134	17.3
3+	145	18.7	144	18.6
Maternal socioeconomic status4					0.46
Upper white collar	89	13.5	106	16.6
Lower white collar	305	46.3	284	44.4
Blue collar	134	20.3	131	20.5
Other	131	19.9	119	18.6
Maternal psychiatric history5					0.0003
No	650	83.6	699	89.9
Yes	128	16.5	79	10.2
Parental psychiatric history5					0.02
No	586	75.3	624	80.2
Yes	192	24.7	154	19.8
	Mean	SD	Mean	SD	P-value2
Gestational weeks at blood draw	10.9	3.47	10.8	3.4	0.49

¹P-value from chi-squared test for difference in proportion of cases and controls across all strata of the covariate

²P-value from t-test for difference between cases and controls

³N missing = 1 Case, 5 Controls

⁴N missing = 119 Cases, 138 Controls

⁵ICD-10 codes F20–25, F28–29, F30–34, F38–39, F84, F40–45, F48, F50–53, F55, F59–66, F68–69, F99, F10–19; ICD-9 codes 295, 296, 297, 298.8A, 298.9X, 300.4, 301.2C, 299, 300–300.3, 300.5–301.1, 301.2 excluding 301.2C, 301.3–301.9, 302, 307.1A, 307.4A, 307.4F, 307.4H, 307.5A–C and 307.5E, 307.8A, 307.9X, 309–309.1, 309.2 excluding 309.2A and 309.2B, 309.2D–309.2F, 309.3–309.9 excluding 309.3A and 309.4A, 312.0A, 312.1–312.2, 312.3 excluding 312.3D, 312.4–312.9, 291–292, 303–305; ICD-8 codes 295, 296, 297, 298.00, 298.10, 298.20, 298.30, 298.99, 299, 300.41, 308, 300.0–300.3, 300.4, 300.5–302.9, 305, 306.40, 306.50, 306.98, 307.99, 291, 303–304.