Meta-analysis for the association between maternal age and the risk of breast cancer. The tests for homogeneity and for publication bias in the studies analyzed are as follows. Maternal age 25 to 29 years: Q = 39.40 (17 degrees of freedom), P < 0.01; Begg test, P = 0.85; Egger test, P = 0.38, Maternal age 30+ years: Q = 67.34 (17 degrees of freedom), P < 0.01; Begg test, P = 0.88; Egger test, P = 0.07. 1The reference for maternal age is ≤24 years old. CI, confidence interval; OR, odds ratio.