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Background: Early maternal cancer and fertility treatment each increase the risk for adverse birth outcomes, but the joint effect of these outcomes has not yet been reported. Thus, the aim was to assess the individual and joint effect of maternal cancer and fertility treatment on the risk for adverse birth outcomes., Methods: This population-based cohort study included 5487 live-born singletons identified in the Danish Medical Birth Register (1994-2016) of mothers with previous cancer (<40 years) recorded in the Danish Cancer Registry (1955-2014). We randomly selected 80,262 live-born singletons of mothers with no cancer <40 years matched to mothers with cancer by birth year and month. We calculated odds ratios (ORs) for preterm birth, low birth weight (LBW) (<2500 g) and small for gestational age (SGA), mean differences in birth weight in grams, and additional cases of preterm birth (gestational age<259 days) per 100,000 person-years. Multiplicative and additive interaction of maternal cancer and fertility treatment was compared with outcomes of children conceived naturally to mothers with no maternal cancer (reference group)., Findings: Among 84,332 live-born singletons, increased ORs for preterm birth were observed among children born to mothers with previous cancer (1·48, 95% confidence interval [CI] 1·33-1.65) or after fertility treatment (1·43, 95% 1·28-1-61), with 22 additional cases of preterm birth among both group of children (95% CI 15-29; 95% CI 14-30). In the joint analyses, the OR for SGA for children born after fertility treatment to mothers with previous cancer was similar to that of the reference group (OR 1·02, 95% CI 0·72-1·44, P for interaction=0·52). Children with both exposures had increased ORs for LBW (1·86, 95% CI 1·17-2·96, P for interaction=0·06) and preterm birth (2·31, 955 CI 1·66-3·20, P for interaction = 0·56), with 61 additional cases of preterm birth (95% CI 27-95, P for interaction=0.26) over that of children in the reference group. The mean birth weight was also lower in children born to mothers with both exposures (-140 g, 95% CI -215; -65) ( P for interaction=0.06) but decreased to -22 g (95% CI -76; 31) after adjustment for GA., Interpretation: Although we did not find any statistically significant additive interaction between maternal cancer and fertility treatment, children born after fertility treatment of mothers with previous cancer were at increased risk for adverse birth outcomes. Thus, pregnant women with both exposures need close follow-up during pregnancy., Funding: The Danish Cancer Society and the Danish Childhood Cancer Foundation., Competing Interests: After finalizing her master thesis and this study, Cathrine Everhøj started as a full time employee at Danske Regioner, which is a public employer organization of the five regions in Denmark responsible for the healthcare system. Filippa Nyboe Norsker and Sofie de Fine Licht have finalized their postdoctoral work and started as full time employees at the Danish Medicines Council and AstraZeneca, respectively. None of the other authors has any conflicts of interest., (© 2022 The Author(s).)

Background: During the past 4 decades, there has been a growing focus on preserving the fertility of patients with childhood cancer; however, no large studies have been conducted of live births across treatment decades during this period. Therefore, the authors estimated the potential birth deficit in female childhood cancer survivors and the probability of live births., Methods: In total, 8886 women were identified in the 5 Nordic cancer registries in whom a childhood cancer had been diagnosed during 1954 through 2006. A population comparison cohort of 62,903 women was randomly selected from the central population registries matched by age and country. All women were followed for live births recorded in medical birth registries. The cumulative probability and the risk ratio (RR) with 95% confidence intervals (CIs) of a live birth were calculated by maternal age across treatment decades., Results: The probability of a live birth increased with treatment decade, and, at age 30 years, the rate for survivors most recently diagnosed was close to the rate among the general population (1954-1969: RR, 0.65 [95% CI, 0.54-0.78]; 1970s: RR, 0.67 [95% CI, 0.60-0.74]; 1980s: RR, 0.69 [95% CI, 0.64-0.74]; 1990s: RR, 0.91 [95% CI, 0.87-0.95]; 2000s: RR, 0.94 [95% CI, 0.91-0.97])., Conclusions: Female childhood cancer survivors had a lower probability of a live birth than women in the general population, although, in survivors diagnosed after 1989, the probability was close to that of the general population. Because the pattern of live births differs by cancer type, continuous efforts must be made to preserve fertility, counsel survivors, and refer them rapidly to fertility treatment if necessary., Lay Summary: The purpose of this study was to compare the probability of giving birth to a liveborn child in female survivors of childhood cancer with that of women in the general population. Survivors of childhood cancer had a lower probability of live births than women in the general population, although survivors diagnosed after 1989 had a probability close to that of the general population. Continuing focus on how to preserve the potential for fertility among female patients with childhood cancer during treatment is important to increase their chances of having a child., (© 2021 American Cancer Society.)