The sperms enter through vaginal passage during sexual intercourse. They travel upwards and reach oviduct where they may encounter the egg. The sperm may fuse with the egg and form a zygote. The zygote gets implanted in the lining of uterus and starts to divide. The mother's body is designed to undertake the development of the child for which the uterus prepares itself every month to receive and nurture the growing child.