Fertilization: Sperm Penetrates Egg. It takes about 24 hours for a sperm cell to fertilize an egg. When the sperm penetrates the egg, the surface of the egg changes so that no other sperm can enter. At the moment of fertilization, the baby's genetic makeup is complete, including whether it's a boy or girl.
Implantation bleeding is an early sign of pregnancy and only experienced by 1/3 of women. Discover when and what to look for as a sign of implantation. Implantation bleeding is an early sign of pregnancy and only experienced by 1/3 of women.
Timing of Implantation Bleeding. The time when implantation bleeding occurs is typically within the first two weeks after fertilization, up to the time that the woman expects her menstrual period. Due to the timing, implantation bleeding could also be mistaken for an extremely light menstrual period in some women.