What factors are needed to achieve a spontaneous pregnancy?

There are 4 basic events that must happen for a woman to become pregnant. The first is she must release an egg from one of her ovaries, a process called ovulation. Second is a sperm from a male must reach the egg and fertilize it to achieve conception. Third, the developing embryo while still in the cellular stages must pass through the fallopian tube where it was fertilized and be released into the uterus. Last, the developing embryo must implant into the wall of the uterus, called the endometrium, in a process called implantation. If any of these four events are altered in any way, pregnancy either will not happen or result in a miscarriage.