Table 3. Multivariable Associations of Parity With Early Menopause in the Nurses’ Health Study II, 1989-2015^a.

Parity	Cases, No.	Person-Years	Model 1		Model 2b		Model 3c
			HR (95% CI)	P Value for Trend	HR (95% CI)	P Value for Trend	HR (95% CI)	P Value for Trend
0	624	193 733	1 [Reference]	<.001	1 [Reference]	<.001	1 [Reference]	.006
1	423	142 831	0.87 (0.77-0.99)		0.86 (0.76-0.97)		0.92 (0.79-1.06)
2	929	317 516	0.78 (0.70-0.86)		0.77 (0.69-0.85)		0.84 (0.73-0.96)
3	441	162 176	0.70 (0.62-0.79)		0.70 (0.61-0.79)		0.78 (0.67-0.92)
≥4	154	56 049	0.69 (0.58-0.83)		0.70 (0.59-0.84)		0.81 (0.66-1.01)

Abbreviation: HR, hazard ratio.

^aParity was defined as the number of pregnancies lasting at least 6 months.

^bAdjusted for age, age at menarche (ie, ≤9, 10, 11, 12, 13, 14, 15, 16, or ≥17 years), smoking status (ie, never, past [1-14, 15-24, or ≥25 years], or current [1-14, 15-24, or ≥25 years]), alcohol intake (ie, 0, 1 to <10, 10 to <30, or ≥30 g/d), vegetable protein intake (in quintiles), body mass index (ie, <18.5, 18.5-24.9, 25.0-29.9, or ≥30), vitamin D from dairy foods (in quintiles), supplemental vitamin D (ie, 0, >0 to <600, or ≥600 IU/d), OC use (ie, never, past, or current), duration of OC (ie, never, 1-23, 24-47, 48-71, 72-95, 96-119, ≥120 months, or missing), and infertility because of ovulatory disorder (ie, yes or no).

^cAdditionally adjusted for total duration of breastfeeding (ie, <1, 1-3, 4-6, 7-12, 13-18, 19-24, 25-36, or ≥36 months, or parous but breastfeeding data missing).