International Journal of Preventive Medicine (Int J Prev Med)2008-78021322022040926192619ENDepartment of Midwifery, School of Nursing & Midwifery, Mashhad University of Medical Sciences, MashhadDepartment of Epidemiology, School of Public Health, Mashhad University of Medical Sciences, MashhadDepartment of Biostatistics, School of Health, Mashhad University of Medical Sciences & Social Determinants of Health Research Center, Mashhad University of Medical Sciences, MashhadCancer Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, MashhadBehavioral Sciences Research Center, Life style institute, Baqiyatallah University of Medical Sciences, Tehran & Nursing Faculty, Baqiyatallah University of Medical Sciences, TehranDepartment of Midwifery, School of Nursing & Midwifery, Mashhad University of Medical Sciences & Nursing and Midwifery Care Research Center, Mashhad University of Medical Sciences, Mashhad20220409<strong>Background</strong>: Breast cancer (BC) is the most frequent cancer in Iranian females. Due to the changes in lifestyle and reproductive risk factors, the BC incidence rate has been rapidly increasing. Knowing risk factors of BC could significantly contribute to improve preventive behaviors. To investigate the relationship between menstrual and reproductive factors and BC in Iranian female population. <strong>Methods</strong>: Web of Science, PubMed, Scopus, and SID as well as references of included studies were searched. Among relevant published observational studies, 27 studies met the inclusion criteria. Pooled risk estimates for the risk factors were determined using random‑effects models due to the presence of substantial heterogeneity (P &lt; 0.05). <strong>Results</strong>: All of the selected studies had case– control design. There was a positive relationship between maternal age at first pregnancy and risk of BC (OR = 1.79 95% CI: 1.36–2.35). Also, menopausal status was associated with higher risk of BC (OR = 1.60 95% CI: 1.18–2.17), whereas, there was no association between menarche age and increased risk of BC (OR = 0.55 95% CI: 0.29–1.03). History of abortion (OR = 1.21 95% CI: 0.97–1.5), nulliparity (OR = 1.43 95% CI: 0.89–2.31), and breastfeeding history (OR = 0.68 95% CI: 0.42–1.09) were not associated with BC risk. <strong>Conclusions</strong>: Our findings suggest that age at the first pregnancy and menopausal status were significantly associated with BC risk among Iranian women, whereas menarche age, nulliparity, and history of breastfeeding were not. In regard to the history of abortion, our findings revealed no association with BC, but in high‑quality studies, this relationship was significant.http://ijpm.mui.ac.ir/index.php/ijpm/article/view/2619http://ijpm.mui.ac.ir/index.php/ijpm/article/download/2619/717718459