Chemotherapy and radiation treatments are known to affect sperm counts, quality, and sexual activity, but experts have not studied the effect of these treatments on a developing fetus.
One 2019 study found that while experts can assume developmental issues for the fetus can occur, there doesn't appear to be a significant increase in these issues among children conceived by people after testicular cancer in general.
But people with one particular form of testicular cancer — testicular germ cell cancer — did conceive children with higher rates of developmental issues for the fetus, regardless of their cancer treatment.