Pregnancy-related factors and the risk of breast carcinoma in situand invasive breast cancer among postmenopausal women in the California Teachers Study cohort

Table 1 Age-adjusted^a percent distribution of baseline characteristics

	Total	Ever pregnant, %		Parous women (number of full-term pregnancy/age at first full-term pregnancy, yrs), %
		No	Yes	< 3/< 25	< 3/≥ 25	≥ 3/< 25	≥ 3/≥ 25
		(n = 8,937)	(n = 43,527)	(n = 8,034)	(n = 14,825)	(n = 10,851)	(n = 7,372)
Race
White	46,624	16.8	83.2	19.8	34.4	28.2	17.7
African-American	1,622	11.1	88.9	25.9	34.6	28.3	11.2
Others	4,218	17.2	82.8	17.7	36.0	27.9	18.4
First-degree family history of breast cancer
No	43,489	16.6	83.4	19.8	34.5	28.3	17.3
Yes	7,132	16.8	83.2	19.2	34.5	27.0	19.3
Unknown	1,843	17.8	82.2	20.8	35.7	27.7	15.9
Age at menarche, years
< 13	26,220	16.9	83.1	20.6	34.3	28.7	16.4
≥ 13	26,244	16.4	83.6	19.0	34.8	27.6	18.7
BMI, kg/m²
< 25	27,583	16.9	83.1	20.4	35.8	26.6	17.2
25 to 29.9	14,354	15.8	84.2	19.1	32.6	30.0	18.3
≥ 30	7,783	17.5	82.5	19.1	33.4	30.6	16.9
Unknown	2,744	16.0	84.0	18.7	35.6	26.7	19.0
Menopausal HT use
Never	10,945	20.4	79.6	16.0	35.5	27.3	21.2
E only	15,676	15.6	84.4	21.8	31.2	30.4	16.7
E plus P only	14,959	15.8	84.2	19.8	37.7	25.8	16.7
Mixed use	7,169	15.7	84.3	21.1	32.7	30.3	15.9
Unknown type of HT	3,715	15.2	84.8	19.8	35.7	26.7	17.8
Duration of breastfeeding for parous women, months
Never	12,628	-	-	25.0	39.7	22.0	13.3
< 6	11,202			24.1	35.2	26.8	13.9
6 to 11	7,124			19.5	38.2	26.9	15.4
12 to 23	6,486			11.1	28.4	35.3	25.2
≥ 24	3,642			3.3	17.2	44.2	35.3

Results are for 52,464 postmenopausal women in the California Teachers Study followed between 1995 and 2007.^aAge distribution in each category of the baseline characteristic variables was adjusted according to age distribution of the 52,464 participants. Abbreviations: BMI, body mass index; HT, hormone therapy; E, estrogen; P, progestin.

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