Table 5.

Association between various reproductive, hormonal, and surgical exposures and risk of postmenopausal breast cancer among women who underwent natural menopause

ExposureUnivariate OR (95%CI)PMultivariate OR (95%CI)P
Oophorectomy, ever/never0.13 (0.02–0.54)0.0060.13 (0.03–0.57)a0.007
Parity, per birth0.97 (0.83–1.13)0.700.97 (0.83–1.13)b0.69
Breastfeeding, per monthc0.99 (0.97–1.01)0.16
Oral contraceptive use, ever/never0.77 (0.46–1.27)0.300.89 (0.52–1.50)d0.66
Age at menarche, per yearc0.91 (0.81–1.03)0.14
  • aEstimate adjusted for parity (per birth) and oral contraceptive use (ever/never).

  • bEstimate adjusted for oophorectomy (ever/never) and oral contraceptive use (ever/never).

  • cTwo of the 3 cases that had an oophorectomy had missing data on breastfeeding and one case had missing data on age at menarche and thus were excluded from the multivariate model for these exposures.

  • dEstimate adjusted for oophorectomy (ever/never) and parity (per birth).