Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 53 9 2024 09 03 2030 2039 EN Doudou Zhao 1. Translational Medicine Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710061, China 2. Assisted Reproduction Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710003, China Jie Chen Department of Epidemiology and Biostatistics, School of Public Health, Xi’an Jiaotong University Health Science Center, Xi’an, Shaanxi, 710061, China Xiayang Li Department of Epidemiology and Biostatistics, School of Public Health, Xi’an Jiaotong University Health Science Center, Xi’an, Shaanxi, 710061, China Zhaofang Li Department of Epidemiology and Biostatistics, School of Public Health, Xi’an Jiaotong University Health Science Center, Xi’an, Shaanxi, 710061, China Jingchen Zhang Graduate Department, Xi’an Medical University, Xi’an, Shaanxi, 710021, China Caixia Gao Graduate Department, Xi’an Medical University, Xi’an, Shaanxi, 710021, China Wenbo Hong Graduate Department, Xi’an Medical University, Xi’an, Shaanxi, 710021, China Danmeng Liu 1. Translational Medicine Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710061, China 2. Assisted Reproduction Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710003, China Wenhao Shi 1. Translational Medicine Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710061, China 2. Assisted Reproduction Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710003, China Juanzi Shi 1. Translational Medicine Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710061, China 2. Assisted Reproduction Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710003, China Pengfei Qu 1. Translational Medicine Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710061, China 2. Assisted Reproduction Center, Northwest Women’s and Children’s Hospital, Xi’an, Shaanxi, 710003, China 3. Central Laboratory, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Chaoyang, Beijing, China 2023 09 25 2023 12 03 Background: Advanced maternal age decreased success of pregnancy rate in the assisted reproductive technology (ART) treatment. We aimed to investigate the association between age and miscarriages in women who required ART for conception. Methods: A cohort study was conducted using a 10-year sample of 14,898 pregnancy cycles with ART treatment in Xi’an, China. The effects of women’s age on miscarriage were assessed using Poisson regression models. The threshold effect between age and miscarriage was explored through curve fitting. Results: Compared with lower than 30 years, the risks of early miscarriage and miscarriage were higher in the older age groups (early miscarriage: [35-37 years: RR=1.48, 95% confidence interval (CI): 1.26 to 1.74; ≥38 years: RR=2.25, 95% CI: 1.87 to 2.72]; miscarriage: [35-37 years: RR=1.45, 95%CI: 1.24 to 1.69; ≥38 years: RR=2.17, 95%CI: 1.82 to 2.60]). The nonlinear relationship between age and early miscarriage and miscarriages were observed. The risk of early miscarriage and miscarriage rapidly increased with age after the turning point (age=33 years) (<33 years: [early miscarriage: RR=1.02, 95% CI: 1.00 to 1.04; miscarriage: RR=1.02, 95% CI: 1.00 to 1.03]; ≥33 years: [early miscarriage: RR=1.11, 95% CI: 1.08 to 1.13; miscarriage: RR=1.10, 95% CI: 1.07 to 1.13]). Conclusion: Among pregnancy cycles undergoing ART, advanced age is associated with higher risk of early miscarriage and miscarriage, and nonlinear relationship between age and early miscarriage and miscarriage were found. More attention should be paid to the risk of pregnant women with older than 33 years in ART treatment. https://ijph.tums.ac.ir/index.php/ijph/article/view/33265 https://ijph.tums.ac.ir/index.php/ijph/article/download/33265/8342