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.
Implantation bleeding is thought to happen when the fertilized egg attaches to the lining of the uterus. Implantation bleeding usually occurs around the time you would expect to have a menstrual period. However, implantation bleeding is lighter than menstrual bleeding. Some women don't experience implantation bleeding and others don't notice it. It's also possible to mistake implantation bleeding for a light period.