Table 2.

Coefficients of confounders, with adjustment for other confounders, season of conception, and duration of pregnancy.

Variable	Reference category	Coefficient	Standard error	HR	95% CI
Smoked then quit	Nonsmoker	$-0.10$	0.03	0.91	(0.85, 0.97)
Smoked throughout or at end of pregnancy	Nonsmoker	$-0.50$	0.03	0.61	(0.57, 0.64)
North	Southeast region	0.18	0.04	1.19	(1.09, 1.30)
West coast	Southeast region	$-0.05$	0.03	0.96	(0.90, 1.01)
Years of education between 10 and 14	Lowest education	$-0.01$	0.03	0.99	(0.94, 1.04)
Years of education $\ge 15$	Lowest education	$-0.24$	0.03	0.78	(0.74, 0.83)
Primiparous	Parous	0.71	0.03	2.04	(1.94, 2.15)
Mother's age		$-0.11$	0.01	0.89	(0.87, 0.92)
Mother's age squared		0.002	0.0002	1.00	(1.00, 1.00)
Married or living together as married	Not married or living together	0.01	0.03	1.01	(0.95, 1.07)
Interaction between primiparity and north		$-0.09$	0.06	0.91	(0.82, 1.02)
Interaction between primiparity and west coast		0.06	0.04	1.06	(0.99, 1.14)