Table 4. Reproductive and lifestyle factors versus risk of endometriosis.

		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)				0.998	0.980–1.02			0.979	0.956–1.00	χ2 = 2.9 P = 0.238
Age at menarche (years)	≤11	47	0.003	0.811	0.559–1.18	30	0.148	1.12	0.677–1.85	χ2 = 11.4 P = 0.077
	12	74		ref.		33		ref.
	13	43		0.730	0.499–1.07	28		1.10	0.661–1.83
	≥14	31		0.504	0.329–0.771	23		0.850	0.495–1.46
Length of menstrual cycle at 18–22 years of age (days)	≤25	23	<0.001	1.17	0.750–1.83	14	0.017	1.23	0.694–2.19	χ2 = 18.5 P = 0.005
	26–31	134		ref.		77		ref.
	32–49	28		0.580	0.385–0.875	15		0.520	0.298–0.906
	≥50	10		0.518	0.271–0.992	8		0.649	0.311–1.36
Smoking at 30 years of age	Never	137	0.628	ref.		70	0.007	ref.		χ2 = 7.1 P = 0.028
	Ever	58		1.14	0.834–1.55	44		1.64	1.12–2.40
BMI at 18 years of age	<18.5	16	0.767	0.674	0.399–1.14	14	0.838	1.03	0.579–1.84	χ2 = 3.1 P = 0.538
	≥18.5 and <22.5	135		ref.		74		ref.
	≥22.5	44		0.832	0.589–1.18	26		0.898	0.571–1.41

BMI, body mass index; CI, confidence interval.