The development of pregnancy in humans begins with the fertilization of a female egg by a male sperm. Fertilization is possible after ovulation - the release of the egg from the ovary. Usually, ovulation occurs on the 10-16th day of the menstrual cycle (from the 1st day of the last menstruation), but can be significantly shifted. The life span of an egg is about a day, and that of a sperm cell is 3-5 days. After ovulation, the egg enters the fallopian tube, where it meets the sperm and fertilization occurs. Then, within 14 days, the fertilized egg moves into the uterus in order to implant (fix) in the uterine cavity and continue to develop.