Table 3.

Unadjusted and adjusted ORs and variables associated with smoking

	Unadjusted analysis							Adjusted analysis*
	Non-smokers†	Self-reported smokers‡			Misclassification§			Self-reported smokers‡		Misclassification§		Both¶
	N	N	OR	95% CI	N	OR	95% CI	OR	95% CI	OR	95% CI	OR	95% CI
Total	1755	418	–		90	–		–		–		–
Cohort
Asturias	326	75	1	–	15	1	–	1	–	1	–	1	–
Gipuzkoa	467	65	0.60	0.42 to 0.88	13	0.60	0.27 to 1.36	0.77	0.52 to 1.15	0.63	0.28 to 1.42	0.75	0.52 to 1.09
Sabadell	466	99	0.92	0.66 to 1.29	26	1.21	0.61 to 2.44	0.68	0.47 to 0.99	0.81	0.40 to 1.64	0.72	0.51 to 1.02
Valencia	496	179	1.57	1.15 to 2.15	36	1.58	0.82 to 3.07	0.94	0.67 to 1.33	0.84	0.43 to 1.66	0.95	0.69 to 1.31
Age
≤ 24	93	43	1	–	18	1	–	1	–	1	–	1
25–29	537	152	0.62	0.40 to 0.94	28	0.27	0.14 to 0.53	0.87	0.55 to 1.38	0.36	0.18 to 0.73	0.73	0.49 to 1.11
30–34	792	153	0.42	0.27 to 0.64	28	0.18	0.09 to 0.36	0.75	0.48 to 1.19	0.26	0.13 to 0.54	0.61	0.41 to 0.92
≥ 35	332	70	0.46	0.29 to 0.73	16	0.25	0.12 to 0.54	0.90	0.54 to 1.49	0.46	0.21 to 1.04	0.76	0.48 to 1.19
				(**p<0.001)			(**p = 0.001)
Country of birth
In Europe	1637	410	1	–	83	1	–	1	–	1		1	–
Outside Europe	114	8	0.28	0.13 to 0.60	7	1.21	0.50 to 2.79	0.25	0.12 to 0.54	1.11	0.46 to 2.65	0.39	0.21 to 0.69
Level of education
University	695	59	1	–	22	1	–	1	–	1	–	1	–
Secondary	703	192	3.22	2.36 to 4.39	41	1.84	1.09 to 3.17	2.37	1.70 to 3.29	1.17	0.66 to 2.08	2.08	1.55 to 2.78
Primary or less	355	165	5.47	3.96 to 7.57	27	2.40	1.34 to 4.32	3.30	2.31 to 4.70	1.02	0.53 to 1.97	2.72	1.97 to 3.74
				(p**<0.001)			(p**=0.002)
Social class
I+II (highest)	438	41	1	–	13	1	–	–		–		–
III	469	96	2.19	1.48 to 3.22	19	1.36	0.67 to 2.80	–		–		–
IV+V (lowest)	847	281	3.54	2.50 to 5.02	58	2.31	1.25 to 4.26	–		–		–
				(p**<0.001)			(p**=0.002)
Year of urine sampling
2004	224	78	1	–	19	1	–	–		–		–
2005	642	179	0.80	0.59 to 1.09	36	0.66	0.37 to 1.18	–		–		–
2006	362	83	0.66	0.46 to 0.94	21	0.68	0.36 to 1.30	–		–		–
2007	399	58	0.42	0.29 to 0.61	13	0.38	0.19 to 0.79	–		–		–
2008	128	20	0.45	0.26 to 0.77	1	0.09	0.01 to 0.70	–		–		–
				(p**<0.001)			(p**=0.001)
Exposure to SHS at home
No	1328	144	1	–	34	1	–	1	–	1	–	1	–
Yes	423	274	5.97	4.75 to 7.51	56	5.17	3.33 to 8.03	4.41	3.44 to 5.64	3.26	2.03 to 5.25	4.39	3.49 to 5.51
Exposure to SHS at work
No	1582	343	1	–	76	1	–	1	–	1		1	–
Yes	172	74	1.98	1.48 to 2.67	14	1.69	0.94 to 3.06	1.55	1.11 to 2.17	1.37	0.72 to 2.59	1.57	1.14 to 2.15
Exposure to SHS elsewhere in leisure time
No	1082	175	1	–	44	1	–	1	–	1	–	1	–
Yes	669	243	2.25	1.81 to 2.79	46	1.69	1.11 to 2.59	1.88	1.44 to 2.34	1.47	0.92 to 2.34	1.80	1.44 to 2.26
Reported having smoked in their life ††
No	862	0	–		17	1	–	–		–		–
Yes	893	418	–		73	4.15	2.43 to 7.09	–		–		–
Reported smoking at the start of pregnancy ††
No	1489	1	–		39	1	–	–		1	–	–
Yes	266	417	–		51	7.32	4.73 to 11.33	–		6.21	3.91 to 9.86	–

Self-reported and misclassification of smoking status.

*Only variables shown in the table were entered in the logistic equation.

†Non-smokers: women who reported that they did not smoke and were found to have urinary cotinine levels of less than 50 ng/ml in the reference group.

‡Smokers: those who reported smoking.

§Misclassification: those who claimed that they did not smoke but were found to have urinary cotinine levels above 50 ng/ml.

¶Both: c+d.

**p for trend.

††Only analysed with regard to misclassification, given the extremely strong association with smoking at the third trimester of pregnancy.

SHS, second-hand smoke.