Table 1.

Age-adjusted Characteristics of 1,420 Participants by Oral Contraceptive Duration at Blood Collection, Nurses’ Health Study II, 1996–1999

Characteristicb	Never	aOC use 1–23 mo	OC use 24–71 mo	OC use 72–119 mo	OC use ≥120 mo	P Value
	(n=277)	(n=275)	(n=462)	(n=238)	(n=146)
Age, yc	39.1 (2.7)	39.4 (2.8)	38.9 (3.0)	39.2 (3.2)	39.4 (2.8)	<0.001
Non-Hispanic white, %	95.3	96.8	96.7	96.7	97.3	0.79
Body mass index	25.2 (.29)	24.7 (.30)	24.5 (.23)	24.9 (.32)	24.2 (.41)	0.30
Alcohol >1 drink/day, %	2.9	1.7	2.5	3.7	4.7	0.52
Current smoker, %	2.5	7.6	6.5	10.9	9.5	<0.01
Smoking, pack-yearsd	8.4 (1.00)	7.8 (.86)	10.0 (.65)	9.9 (.79)	12.1 (.95)	<0.05
Age at menarche, y	12.5 (.08)	12.6 (.08)	12.5 (.07)	12.4 (.09)	12.6 (.12)	0.25
Age at first OC use, y	N/A	21.8 (.21)	20.9 (.16)	19.4 (.23)	18.7 (.29)	<0.001
Infertility due to ovulatory disorder, %	6.1	4.0	10.0	5.0	6.8	<0.05
Parity	1.8 (.07)	2.1 (.07)	1.9 (.05)	1.8 (.08)	1.4 (.10)	<0.001
Breastfeeding, moe	22.6 (.98)	21.2 (.90)	18.9 (.71)	13.2 (.96)	10.7 (1.32)	<0.001
Tubal ligation, %	14.2	21.8	20.5	29.7	20.2	<0.001

Abbreviation: OC, oral contraceptive.

^aWomen with missing duration of OC use at blood collection (n=22) are not shown.

^bValues are age-adjusted means (SE) unless otherwise indicated.

^cValues are expressed as unadjusted means (SD).

^dAmong past or current smokers.

^eAmong parous women.