Table 5

RRs and 95% CIs of developing breast cancer according to exclusive use of progestin-only oral pills (POPs) or combined OCs (COCs), The Women’s Lifestyle and Health Study

Use of OCsStudy populationBreast cancer casesRR (95% CI)
Age-adjustedMultivariatea
Never-users28,1712611.0 (reference)1.00 (reference)
 Ever-users of
  POPs3,435291.1 (0.8–1.6)1.1 (0.8–1.7)
  COCs42,8114441.3 (1.1–1.5)1.3 (1.1–1.6)
  Both POPs and COCs or missing values on brand28,6102741.2 (1.0–1.4)1.2 (1.0–1.4)
 Current/recent users at start of follow-up
  POPs2,189251.6 (1.1–2.5)1.6 (1.0–2.4)
  COCs6,691601.6 (1.2–2.2)1.5 (1.0–2.0)
 Age-stratified analysis
  Current/recent users at start of follow-up
   Age at start of follow-up 30–39 yrsb
    Never-users8,829411.0 (reference)1.0 (reference)
    POPs1,25181.6 (0.8–3.4)1.7 (0.8–3.7)
    COCs5,130361.9 (1.2–3.1)2.0 (1.2–3.2)
   Age at start of follow-up 40–49 yrs
    Never-users19,3422201.0 (reference)1.0 (reference)
    POPs938171.7 (1.0–2.8)1.6 (0.9–2.6)
    COCs1,561241.5 (1.0–2.3)1.2 (0.7–1.9)
  • a Multivariate analysis, adjusted for: age (continuous variable), parity (0, 1, 2, 3+), age at first birth (−20, 21–24, 25+), age at menarche (continuous variable), use of HRT (ever/never), menopausal status (pre-/postmenopausal), history of breast cancer in first-degree relatives (yes/no), duration of breastfeeding (continuous variable), BMI (continuous variable), region (Sweden and five health regions in Norway), and a term for interaction between BMI and menopausal status.

  • b Exclusive use of progestin-only pills and exclusive use of combined OCs.

  • c Menopausal status and the interaction term between BMI and menopausal status were not included in the multivariate model.