How long does it take for the sperm to reach the uterus and unite with the egg? After sexual intercourse, semen is ejaculated into the posterior fornix of the vagina. Most of the sperm die in the acidic environment of the vagina, and only a small number of sperm pass through the cervix and reach the uterine cavity within 1 hour. In another 1-2 hours, the sperm travels about 18cm to finally reach the abdomen of the fallopian tube where it unites with the egg to form a fertilized egg. This is where new life begins and the baby will start to develop in the uterus for the next 266 days. On day 2 the baby begins to develop safely, cell division begins and the sperm finishes reaching the uterus.