Chemotherapy kills cells that divide quickly. This targets cancer cells, but inadvertently affects sperm cells as well. Some chemo drugs may halt sperm production and cause azoospermia within 3 months, while others can reduce sperm motility. Chemo can also damage germ cells and affect sperm production in children. Finally, chemotherapy is likely to damage the DNA carried by sperm.
Depending on the drug you receive and the dose, sperm production may resume in 15 to 49 months. If chemo damages all the stem cells in the testicles that make new sperm, infertility may be permanent.