Sperm can survive for up to 72 hours after ejaculation, but the egg can survive for no more than 24 hours after ovulation. If sperm reach the fallopian tube too early,. The precise timing depends on how long the egg lives and how quickly the sperm reaches the egg. But in almost all cases, IUI fertilization will. As a woman ages, the quantity and quality of her eggs decline. And even if sperm do reach an egg, they may not be able to penetrate the egg's covering. If a sperm manages to fertilize the egg during its journey, it implants in the uterine lining and grows to become a fetus. If not, the egg disintegrates.