Impact of cancer during reproductive age on the probability of livebirth after cancer: a register-based cohort study among Danish women aged 18–39 with and without cancer

Purpose: This register-based study investigates the probability of a livebirth after cancer during the female reproductive age. Methods: The study population, derived from the DANAC II cohort, included women aged 18–39 diagnosed with cancer between 1978 and 2016, matched with 60 undiagnosed women each from the general population. Primary outcome was a livebirth after cancer with follow-up until death, emigration, or end of follow-up. Hazard ratios (HR) were calculated using multivariable Cox regression analyses. Results: The population included 21,596 women with cancer and 1,295,760 without. The 20-year cumulative incidence of livebirth after cancer/study entry was lower among women with cancer (0.22 [95% CI 0.22–0.22]) compared to those without (0.34 [95% CI 0.34–0.34]). The HR of a livebirth after cancer was 0.61 [95% CI 0.59–0.63]; highest at age 18–25 (HR = 0.72 [95% CI 0.68–0.76]); and lowest at age 33–39 (HR = 0.50 [95% CI 0.47–0.54]). Nullipara women had higher HR of a livebirth than those with children (HR = 0.72 [95% CI 0.69–0.75] vs. HR = 0.48 [95% CI 0.46–0.51]). HR was lowest for women with breast, gynecological, central-nerve-system cancer, and leukemia. Women with/without cancer were comparable in assisted reproductive technology initiation after cancer/study entry, but HR was higher among nullipara than in those with prior children. Conclusions: Cancer during reproductive years significantly and negatively impacts HR of a livebirth after cancer, particularly as age at diagnosis increases. Low HR of livebirth is observed in specific cancer groups. Implications for Cancer Survivors: Results underscore the importance of oncofertility counseling at diagnosis, referral to fertility specialist before treatment, and follow-up after cancer, focusing on cancer type, parity status, and age at diagnosis.