Main results
In our dose-response meta-analysis, six cancers from 46 studies were found to had significant associations with the birth weight. (Ovarian cancer: RR: 1.21, 95%CI: 1.01-1.44; breast cancer: RR: 1.12, 95%CI: 1.08-1.16; colorectal cancer: RR: 1.20, 95%CI: 1.01-1.43; endometrial cancer: RR: 0.85, 95%CI: 0.78-0.93; prostate cancer: RR: 1.27, 95%CI: 1.01-1.61; testicular cancer: RR: 1.21, 95%CI: 1.03-1.43). As the birth weight gain, the slope of the dose-response curve of breast cancer increased continuously and the curve of testicular cancer was U-shaped. (Pnonlinearity<0.001) In the MR study, seven cancers were included. Only invasive mucinous ovarian cancer was found to have casual effect on birth weight (OR: 0.62; 95%CI: 0.39-0.97) while other cancers did not.