Preterm Birth and Breast Cancer Risk: A Systematic Review and Meta-Analysis

Background: The characteristics of pregnancy, such as gestational age are related to the level of maternal hormones, which levels of these hormones can be associated with breast cancer (BC) risk. Therefore, the aim of this study was to determine the relationship between the preterm birth (PB) and BC risk in women in a systematic review and meta-analysis. Methods: In this systematic review and meta-analysis, published studies were located back to the earliest available publication date (1983), using the Medline/PubMed, Embase, Scopus and Web of Science (Clarivate analytics) bibliographic databases. Eligibility, methodological quality, and data extraction were done by two independent reviewers, and finally, to calculate the pooled estimates, Meta-analysis was performed. Results: Thirteen studies including a total of 2,845,553 women were included in this meta-analysis. Pooled results suggested that PB could increase the risk of BC (RR= 1.03, 95% CI: 1.00, 1.07; I2= 62.5%). Risk was significantly increased in women with a PB at >37 gestational weeks (RR = 1.03, 95% CI: 1.01, 1.06) and 26-31 gestational weeks (RR = 1.03, 95% CI: 1.01, 1.06) compared to those with 40-41 gestational weeks. A significant increment in the risk of BC in uniparous women with a PB (RR = 1.05, 95% CI = 1.01, 1.08) and women with >45 years (RR = 1.12, 95% CI = 1.01, 1.24) was observed. Conclusions: The results of this study supported the higher risk of BC in all woman with PB, primiparous women and women with >45 years. Therefore, more care and screening for early detection of the disease is recommended in these women.