Birth weight and the risk of overall breast cancer, premenopausal and postmenopausal breast cancer in adulthood: a dose-response meta-analysis of observational studies

The effect of birth weight on breast cancer across different menopausal states remains unknown.The aim of this study was to systematically evaluate the association of birth weight with the risk of overall breast cancer (OBC) and premenopausal and postmenopausal breast cancer during adulthood. In parallel, the dose-response analyses were performed.Relevant studies were systematically searched from the PubMed, Embase, and the Cochrane Library databases from the inception to May 25, 2021, without language restrictions. All the results were pooled according to risk ratios (RRs).In total, 21 cohort studies comprising 1,139,032 participants were included. An increase in the birth weight was not associated with the risk of OBC and premenopausal and postmenopausal breast cancer. Compared with women having normal weight at birth, those with a high birth weight are likely to have an increased risk of invasive breast cancer (RR: 1.19, 95% confidence intervals: 1.03-1.38; I2: 28.6%). The dose-response analyses showed that the risk of premenopausal breast cancer increased significantly in unknown singleton status with birth weight over 2850 g (RR: 1.14 [1.02-1.30]). Similarly, postmenopausal breast cancer risk was increased in singleton births with birth weight over 3750 g (RR: 1.21 [1.00-1.47]).High weight at birth might be not significantly associated with the risk of OBC, premenopausal and postmenopausal breast cancer and ER+ and ER- breast cancer but is positively associated with the risk of invasive breast cancer, regardless of parity. Furthermore, with an increase in birth weight, the risk of postmenopausal breast cancer is likely to increase in the singleton births, whereas the risk of premenopausal breast cancer is likely to increase in unknown singleton status.