TABLE B-10 Relative Risks of Breast Cancer in Parous Women Who Have Ever Used Oral Contraceptives by Age at First Live Birth

 

Age in Years at First Live Birth

First Author/Date (Study Design)

<20

20-24/<24

25-29/>25

>30

Trapido/1981 (cohort)

0.5

0.7

1.2

0.6

Miller/1989 (case-control)

2.9 a

2.1 a

2.6 a

N.a.

Stanford/1989 (case-control)

0.74

0.93

1.09

1.04

WHO b /1990 (case-control)

N.a.

1.17

1.27

1.13

N.a: Not available.

a Confidence intervals of 95 percent exclude 1.0.

b WHO = World Health Organization.

Table B-13, Miller and colleagues (1989) observed a trend of increasing relative risks in relation to oral contraceptive use with increasing body mass index. This trend was not observed by Stanford and colleagues (1989). The former study was restricted to women under age 45, when obesity has a minimal impact on risk of breast cancer; the latter study included older women.

Table B-14 shows the results of studies that assessed risk of breast cancer in oral contraceptive users with a history of benign breast disease. Risks were elevated in all three studies that confined analyses to young women (Lees et al., 1978; Paffenbarger et al., 1980; Janerich et al., 1983) with two of the studies showing an increasing risk with

TABLE B-11 Relative Risks of Breast Cancer in Women Who Have Ever Used Oral Contraceptives by Number of Children

 

Number of Children

First Author/Date (Study Design)

0

1/>1

1-2

2-3/>3

>4

La Vecchia/1986 (case-control)

1.16

1.00

N.a.

N.a.

N.a.

Kay/1988 (cohort)

1.14

5.88 a

N.a.

1.01

0.71

Miller/1989 (case-control)

N.a.

N.a.

2.4 a

2.9 a

N.a.

N.a.: Not available.

a Confidence intervals of 95 percent exclude 1.0.



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