. Author manuscript; available in PMC: 2023 Jan 3.

Published in final edited form as: Pediatrics. 2021 Aug 11;148(3):e2020032300. doi: 10.1542/peds.2020-032300

Table 3.

Interactions between gestational age at birth and sex (1973–2013) in relation to risk of ASD (1987–2015).

	Gestational age at birth						PRs (95% CI) for early term vs. full-term within sex strata	PRs (95% CI) for preterm vs. full- term within sex strata
	Full-term (39–41 wks)		Early term (37–38 wks)		Preterm (<37 wks)
	Prev.^a (Cases)	PR (95% CI)^b	Prev.^a (Cases)	PR (95% CI)^b	Prev.^a (Cases)	PR (95% CI)^b
Sex
Female	0.9% (12,292)	Reference	1.1% (3,768)	1.15 (1.11, 1.19); P<0.001	1.5% (1,318)	1.52 (1.44, 1.61); P<0.001	1.15 (1.11, 1.19); P<0.001	1.52 (1.44, 1.61); P<0.001
Male	1.8% (25,648)	2.02 (1.98, 2.07); P<0.001	2.1% (7,683)	2.24 (2.18, 2.30); P<0.001	2.7% (2,829)	2.74 (2.63, 2.85); P<0.001	1.11 (1.08, 1.13); P<0.001	1.35 (1.30, 1.40); P<0.001
PRs (95% CI) for female vs. male within gestational age strata		2.02 (1.98, 2.07); P<0.001		1.95 (1.87, 2.02); P<0.001		1.80 (1.68, 1.91); P<0.001
Interaction on additive scale: RERI (95% CI)			0.07 (0.00, 0.14); P=0.05		0.19 (0.06, 0.32); P=0.004
Interaction on multiplicative scale: PR ratio (95% CI)			0.96 (0.92, 1.01); P=0.09		0.89 (0.83, 0.95); P<0.001

Cumulative prevalence.

Adjusted for birth year, sex, birth order, maternal factors (age, education, BMI, preeclampsia, other hypertensive disorders, diabetes), paternal factors (age, education), and family history of ASD.

PR = prevalence ratio, RERI = relative excess risk due to interaction