Table 5.

Analysis of perinatal characteristics for an association with ASD-R among individuals whose mothers had research authorization (N=6851).

Characteristic	Total person-years prior to age 21 years	No. meeting criteria for ASD-R by age 21 years	Univariate analysis		Multivariable analysis
			Unadjusted HR (95% CI)	P-value	Adjusted HR (95% CI)	P-value
Infant characteristics
Sex				<0.001		<0.001
Male	55,103	158	3.09 (2.25, 4.24)		3.11 (2.26, 4.28)
Female	54,378	50	Referent		Referent
Gestational age				0.13		0.40
Extremely preterm (23–27 weeks)	324	2	3.69 (0.91, 14.97)		2.25 (0.52, 9.82)
Very preterm (28–31 weeks)	863	3	2.16 (0.68, 6.81)		1.45 (0.44, 4.82)
Moderate to late preterm (32–36 weeks)	8,291	21	1.58 (0.98, 2.53)		1.38 (0.85, 2.23)
Early term (37–38 weeks)	20,208	41	1.27 (0.88, 1.82)		1.22 (0.84, 1.77)
Full term (39–40 weeks)	60,431	97	Referent		Referent
Late term (41 weeks)	17,584	41	1.45 (1.00, 2.08)		1.47 (1.01, 2.12)
Postterm (42–43 weeks)	1,780	3	1.03 (0.33, 3.26)		0.84 (0.26, 2.69)
Size for gestational agea				0.09		0.22
Small for gestational age	1,802	7	2.02 (0.95, 4.31)		1.64 (0.75, 3.56)
Appropriate for gestational age	77,392	151	Referent		Referent
Large for gestational age	30,287	50	0.85 (0.62, 1.17)		0.93 (0.66, 1.30)
APGAR at 5 minutes				0.15		0.43
Less than	1,047	4	2.06 (0.77, 5.55)		1.53 (0.54, 4.31)
7 or greater	108,433	204	Referent		Referent
Maternal characteristics
Maternal age (years)				0.85		0.10
<20	5,942	13	1.16 (0.66, 2.03)		0.55 (0.28, 1.07)
20–34	85,777	160	Referent		Referent
35+	17,762	35	1.06 (0.74, 1.53)		1.26 (0.86, 1.86)
Married				<0.001		0.008
No	17,517	57	1.94 (1.43, 2.64)		1.67 (1.14, 2.44)
Yes	91,964	151	Referent		Referent
Maternal education level				0.09		0.84
Less than high school	6,877	17	1.48 (0.86, 2.54)		1.13 (0.59, 2.17)
High school graduate	21,559	53	1.54 (1.08, 2.20)		1.17 (0.78, 1.76)
1–3 years of college	30,831	59	1.20 (0.86, 1.69)		1.02 (0.72, 1.46)
4 or more years of college	50,214	80	Referent		Referent
Tobacco use during pregnancy				<0.001		0.11
No	100,198	176	Referent		Referent
Yes	9,283	32	1.96 (1.34, 2.86)		1.41 (0.93, 2.14)
Weight gain during pregnancyb				0.19		0.31
Inappropriately low	4,917	15	1.65 (0.96, 2.82)		1.50 (0.86, 2.63)
Appropriate	88,470	163	Referent		Referent
Inappropriately high	16,093	30	1.03 (0.69, 1.54)		0.94 (0.63, 1.42)
Parityc				0.17		0.23
0	43,258	98	1.39 (0.83, 2.33)		1.58 (0.92, 2.74)
1	36,843	61	1.01 (0.59, 1.74)		1.22 (0.70, 2.13)
2	18,943	32	1.04 (0.58, 1.88)		1.21 (0.67, 2.19)
3+	10,437	17	Referent		Referent
Mode of delivery				0.18		0.56
Vaginal	92,142	168	Referent		Referent
Cesarean section	17,339	40	1.27 (0.90, 1.79)		1.11 (0.78, 1.59)
History of maternal psychiatric disorder				<0.001		0.001
No	95,135	159	Referent		Referent
Yes	14,346	49	2.01 (1.46, 2.77)		1.73 (1.24, 2.42)

Abbreviations: ASD-R, research-identified autism spectrum disorder; CI, confidence interval; HR, hazard ratio

^aSize for gestational age was determined using the sex-specific 10^th and 90^th percentiles from the revised Fenton growth charts for infants with a gestational age 23–36 weeks and the WHO growth charts for infants with a gestational age 37–43 weeks.^22,23

^bWeight gain during pregnancy defined as inappropriately low (<11 pounds for singleton gestation, <25 pounds for multiple gestation), appropriate (11–40 pounds for singleton gestation, 25–54 pounds for multiple gestation), or inappropriately high (≥41 pounds for singleton gestation, ≥55 pounds for multiple gestation).²⁴

^cParity is based on the number of previous deliveries, not counting the delivery of the index infant.