Table 4.

Associations between duration of OC use by estrogen and progestin type and ovarian cancer risk in the Nurses’ Health Study II (1989-2013)^a

			Multivariate-adjusted modelb
	Cases	Person-yrs	HR	95% CI
Never OC users	36	321,519	1.00	(Ref.)
Duration of mestranol usec,d
≤1 year	42	203,173	1.83	(1.16, 2.88)
>1-<5 years	44	330,914	1.09	(0.70, 1.71)
5-<10 years	25	181,313	1.04	(0.62, 1.75)
≥10 years	5	37,056	0.90	(0.35, 2.32)
Duration of ethinyl estradiol usec,e
≤1 year	31	245,293	1.22	(0.75, 1.98)
>1-<5 years	58	466,580	1.25	(0.82, 1.92)
5-<10 years	27	327,298	0.82	(0.49, 1.36)
≥10 years	16	147,750	0.90	(0.49, 1.64)
Duration of 1st generation progestin usef,g
≤1 year	51	279,314	1.72	(1.11, 2.65)
>1-<5 years	67	510,199	1.21	(0.80, 1.82)
5-<10 years	31	342,785	0.82	(0.50, 1.33)
≥10 years	17	131,927	1.02	(0.57, 1.83)
Duration of 2nd generation progestin useh,i
≤1 year	22	183,337	1.22	(0.71, 2.10)
>1-<5 years	37	294,897	1.24	(0.77, 1.98)
5-<10 years	16	156,456	0.97	(0.53, 1.77)
≥10 years	5	48,872	0.78	(0.30, 2.02)

^aDuration of OC use by type of estrogen and progestin is non-exclusive use, e.g. women with ethinyl estradiol use and mestranol use are included in both variables.

^bAdjusted for age (years), calendar time, parity (number of pregnancies), tubal ligation (yes/no), breastfeeding duration (months), missing breastfeeding duration (yes/no), laparoscopically-confirmed endometriosis (ever/never), body mass index (kg/m²)

^cExcludes women who used progestin-only pills exclusively

^dExcludes women who exclusively used ethinyl estradiol

^eExcludes women who exclusively used mestranol

^fFirst generation progestins include norethindrone, norethynodrel, norethindrone acetate, ethynodiol diacetate, medroxyprogesterone acetate, and chlormadinone acetate

^gExcludes women who exclusively used 2^nd generation progestins

^hSecond generation progestins included levonorgestrel and norgestrel

ⁱExcludes women who exclusively used 1^st generation progestins