Skip to main content
. Author manuscript; available in PMC: 2019 Sep 25.
Published in final edited form as: Ann Intern Med. 2018 Dec 11;170(1):22–30. doi: 10.7326/M18-1323

Figure 4. HR for breast cancer according to years since most recent birth, stratified by parity (0, 1, 2, or ≥3 births).

Figure 4.

Nulliparous women are the reference group, and HRs are adjusted for attained age and study; estimates for women with ≥3 births are further adjusted for continuous number of births (3–10 births). Dashed curves correspond to 95% CIs. Vertical lines represent the quadratic spline knots at 6.1, 13.3, 18.4, 23.3, and 29.3 y after birth. Likelihood ratio tests indicated a statistically significant interaction with parity (P = 0.030). For uniparous women, the peak HR was 1.22 (95% CI, 1.03 to 1.45) and occurred 5.3 y after last birth; crossover toward an inverse association occurred 18.5 y (CI, 16.5 to 20.9 y) after first birth for uniparous women. For biparous women, the peak HR was 1.36 (CI, 1.19 to 1.55) at 4.6 y after last birth; crossover toward an inverse association occurred 14.8 y (CI, 12.7 to 17.2 y) after last birth. For women with ≥3 births, the peak HR was 2.12 (CI, 1.75 to 2.56) at 4.2 y after last birth, crossover toward an inverse association occurred 25.0 y since last birth, and the lower bound of the CI crossed over at 22.6 y. HR = hazard ratio.