Table 2.

Crude and adjusted odds ratios for factors associated with postpartum smoking relapse.

	Relapsed	Crude		Adjusted
	%	OR	95%CI	OR	95%CI
Maternal age at delivery (yrs)
<20	12.4	2.93	1.75–4.93	2.77	1.56–4.93
20–24	6.4	1.42	1.11–1.83	1.45	1.10–1.90
25–29	5.3	1.16	0.93–1.45	1.22	0.97–1.54
30–34	4.6	reference		reference
35–39	6.4	1.42	1.11–1.82	1.30	1.01–1.68
≥40	8.8	1.99	1.29–3.07	1.68	1.06–2.65
Maternal education (yrs)
≤12 years	7.2	2.02	1.69–2.42	1.27	1.05–1.55
≥13 years	3.7	reference		reference
Household income (million JPY)
<2	7.7	1.53	1.16–2.02	1.22	0.91–1.64
2–3	6.3	1.25	1.03–1.51	1.14	0.93–1.40
4–5	5.2	reference		reference
6–7	3.3	0.64	0.44–0.91	0.75	0.52–1.08
≥8	3.7	0.71	0.46–1.08	0.78	0.50–1.22
Pre-pregnancy BMI (kg/m2)
<18.5	5.4	1.00	0.80–1.25	0.97	0.77–1.23
18.5–24.9	5.4	reference		reference
≥25	7.3	1.38	1.11–1.73	1.17	0.92–1.48
Fertility treatment
No	5.7	reference		reference
Yes	3.2	0.53	0.29–0.98	0.75	0.40–1.41
Parity
First	3.9	reference		reference
≥Second	7.5	2.01	1.69–2.38	1.84	1.51–2.23
Feeding method at 1 month after delivery
Breast milk	3.7	reference		reference
Breast and formula milk	5.7	1.58	1.31–1.91	1.44	1.19–1.75
Formula milk	20.1	6.61	5.22–8.36	4.05	3.15–5.22
Partner smoking status during pregnancy
Non-smoker	4.7	reference		reference
Quitter before pregnancy	4.0	0.85	0.55–1.33	1.01	0.64–1.60
Quitter during pregnancy	3.8	0.81	0.52–1.27	0.93	0.59–1.48
Smoker	6.2	1.49	1.22–1.83	1.42	1.05–1.92
Number of cigarettes use per day
1–10	4.3	reference		reference
≥11	8.0	1.93	1.64–2.27	1.78	1.50–2.11
Maternal drinking status at 1 months after delivery
Non-drinker	4.7	reference		reference
Drinker	17.7	4.37	3.56–5.36	3.19	2.56–3.97
EPDS score
<9	5.3	reference		reference
≥9	7.1	1.35	1.11–1.64	1.28	1.04–1.57
Spent at parents’ home after delivery
Did not spend or <14 days	6.8	reference		reference
≥14 days	4.2	0.59	0.50–0.70	0.79	0.66–0.96

OR, Odds ratio; 95% CI, 95% Confidence Interval; BMI, Body Mass Index; EPDS, Edinburgh Postnatal Depression Scale.