Table 2

Unadjusted odds ratios of risk factors for SIDS and interaction with time period in Sweden 1973–1996

	I. Rising incidence		II. High incidence		III. Falling incidence		Interaction with time period (p value)
	1973–1980		1981–1992		1993–1996
	(n = 8372)		(n = 13 187)		(n = 4165)
	OR	95% CI	OR	95% CI	OR	95% CI
Smoking in early pregnancy							<0.001
Nil	—	—	1.0	ref	1.0	ref
1–9 cigarettes per day	—	—	1.9	1.6, 2.2	3.1	2.0, 4.8
10+ cigarettes per day	—	—	3.3	2.8, 3.8	9.6	6.5, 14.0
Male sex	1.4	1.1, 1.7	1.5	1.3, 1.7	1.2	0.9, 1.7	0.45
Maternal age							0.09
⩽19 years	2.1	1.5, 3.1	2.2	1.7, 2.8	3.1	1.5, 6.6
20–24 years	1.3	1.0, 1.7	1.1	1.0, 1.3	1.6	1.1, 2.4
25–29 years	1.0	ref	1.0	ref	1.0	ref
30–34 years	1.1	0.8, 1.4	0.9	0.7, 1.0	0.7	0.4, 1.1
35+ years	0.8	0.5, 1.4	0.7	0.6, 0.9	1.3	0.8, 2.1
Parity							0.52
1	1.0	ref	1.0	ref	1.0	ref
2	1.3	1.0, 1.6	1.8	1.5, 2.0	1.6	1.0, 2.4
3	1.6	1.1, 2.1	2.0	1.7, 2.4	2.8	1.8, 4.3
4+	2.8	2.0, 4.1	3.0	2.4, 3.7	4.2	2.6, 6.9
SGA	2.2	1.5, 3.2	2.2	1.7, 2.9	1.6	0.7, 3.8	0.80
Preterm birth	2.0	1,4, 2.9	2.0	1.6, 2.4	4.3	2.8, 6.6	0.005
SGA and preterm birth	3.7	1.9, 7.3	2.6	1.6, 4.4	6.8	2.7, 17.1	0.19