Table 2. Odds ratios (ORs) and 95% confidence intervals (CIs) for gallbladder cancer in relation to reproductive factors by biliary stone status.

	Without biliary stones					With biliary stones
Reproductive factors	Controlsa	Casesa	ORb	(95% CI)b	P-valueb	Controlsa	Casesa	ORb	(95% CI)b	P-valueb	ORc	(95% CI)c	P-valuec
Total	422	36	—	—		123	233	—	—
Parity
0	11	2	—	—		5	2	—	—		—	—
1	67	10	1	Reference		13	16	1	Reference		1	Reference
2	104	4	—	—		20	39	2.02	(0.77–5.31)		1.77	(0.64–4.87)
3 (⩾3 for no stones)	240	20	1.21	(0.25–5.84)		33	43	1.35	(0.52–3.49)		1.23	(0.44–3.43)
4	—	—	—	—		21	53	2.89	(1.02–8.23)		2.55	(0.81–8.05)
5	—	—	—	—		17	42	2.86	(0.95–8.62)		2.38	(0.69–8.15)
⩾6	—	—	—	—		14	37	2.99	(0.93–9.65)		2.43	(0.65–9.07)
P-trendd			—	—	0.57			—	—	0.03	—	—	0.16
P-interaction										0.09
Age at first birth (years) e
⩾27	112	9	1	Reference		32	36	1	Reference		1	Reference
24–26	84	10	1.83	(0.66–5.06)		21	39	1.77	(0.84–3.71)		1.74	(0.81–3.76)
21–23	100	9	1.21	(0.39–3.82)		28	74	2.56	(1.28–5.13)		2.36	(1.12–4.99)
⩽20	115	6	0.59	(0.16–2.22)		36	81	1.96	(0.97–3.95)		1.86	(0.84–4.15)
P-trendd					0.39					0.06			0.13
P-interaction										0.07
Age at menarche (years)
⩽13	79	5	1	Reference		31	26	1	Reference		1	Reference
14–15	149	11	1.10	(0.35–3.43)		44	87	2.29	(1.20–4.40)		2.20	(1.12–4.29)
16–17	136	12	1.32	(0.43–4.03)		34	83	2.71	(1.37–5.33)		2.60	(1.29–5.24)
⩾18	58	8	2.33	(0.67–8.14)		14	33	2.61	(1.12–6.09)		2.28	(0.96–5.39)
P-trendd					0.17					0.02			0.04
P-interaction										0.86
Parity and age at first birth (years)
0–1 and ⩾24	—	—	—	—		10	14	1	Reference		—	—
2–3 and ⩾24	—	—	—	—		31	43	1.47	(0.52–4.16)		—	—
⩾4 and ⩾24	—	—	—	—		12	18	1.86	(0.49–6.94)		—	—
0–1 and ⩽23	—	—	—	—		2	2	—	—
2–3 and ⩽23	—	—	—	—		22	39	1.77	(0.59–5.20)		—	—
⩾4 and ⩽23	—	—	—	—		40	114	3.26	(1.06–10.03)		—	—
Parity and age at menarche (years)
0–1 and ⩽15	—	—	—	—		12	12	1	Reference		—	—
2–3 and ⩽15	—	—	—	—		37	44	1.48	(0.49–4.40)		—	—
⩾4 and ⩽15	—	—	—	—		26	57	3.19	(0.95–10.69)		—	—
0–1 and ⩾16	—	—	—	—		6	6	1.12	(0.21–6.09)		—	—
2–3 and ⩾16	—	—	—	—		16	36	2.56	(0.79–8.21)		—	—
⩾4 and ⩾16	—	—	—	—		26	74	4.01	(1.19–13.58)		—	—

^aGallbladder cancer cases compared with population controls with a gallbladder (n=545).

^bAdjusted for age (continuous), education and body mass index.

^cFurther adjusted for age first birth (continuous), age menarche (continuous) and parity; each factor is not self-adjusted.

^dLinear test of trend using continuous variable.

^eAmong women with at least one full-term birth (n=568 controls).