Table 6. Reproductive and lifestyle factors versus risk of endometriosis in women without a history of infertility.

		Surgically confirmed endometriosis (Group A)				Imaging-diagnosed endometriosis without surgery (Group B)				Wald test between Group A and Group B
		n	Cochran- Armitage trend test	Odds ratio	95% CI	n	Cochran- Armitage trend test	Odds ratio	95% CI
Age (years)				1.00	0.975–1.03			0.987	0.959–1.02	χ2 = 0.8 P = 0.670
Age at menarche (years)	≤11	25	0.053	0.817	0.492–1.36	20	0.406	1.26	0.673–2.36	χ2 = 9.6 P = 0.144
	12	40		ref.		20		ref.
	13	24		0.740	0.444–1.23	23		1.46	0.797–2.67
	≥14	15		0.441	0.242–0.805	16		0.957	0.492–1.86
Length of menstrual cycle at 18–22 years of age (days)	≤25	10	0.045	0.987	0.507–1.92	8	0.217	1.06	0.502–2.24	χ2 = 5.4 P = 0.500
	26–31	71		ref.		52		ref.
	32–49	17		0.665	0.390–1.13	13		0.665	0.361–1.23
	≥50	6		0.605	0.260–1.40	6		0.751	0.319–1.77
Smoking at 30 years of age	Never	73	0.797	ref.		46	0.009	ref.		χ2 = 9.1 P = 0.011
	Ever	31		1.19	0.780–1.82	33		1.96	1.25–3.07
BMI at 18 years of age	<18.5	10	0.525	0.794	0.408–1.54	9	0.740	0.945	0.464–1.93	χ2 = 3.6 P = 0.462
	≥18.5 and <22.5	75		ref.		53		ref.
	≥22.5	19		0.641	0.386–1.07	17		0.818	0.471–1.42

BMI, body mass index; CI, confidence interval.