A pregnancy occurs when reproductive cells from a man and a woman's body become combined inside a woman's uterus. The normal way that this occurs is through sexual intercourse, where the man's penis enters the woman's vagina and ejaculates sperm (the male reproductive cells) into the vagina during the process of orgasm or sexual climax. Microscopic though they are, the sperm are able to move around within the vagina, and make their way through the cervix and into the uterus where, if the timing is just right, a female ovum or egg (the female reproductive cell) is waiting. Sexually mature adult females ovulate (produce eggs) once each month as a part of their normal menstrual cycle. The sperm compete to penetrate the outer membrane or covering of the egg which seals off permanently once a single sperm makes its way inside. The new sperm and egg combination next exchange genetic material to form a unique blueprint for a new human being, producing a fertilized egg that will later attach itself to the wall of the uterus and start growing into a new human being if all goes well. Conception is said to occur at the moment the egg and sperm combine.
Though intercourse is the normal method through which an egg and a sperm get together, modern reproductive medicine has opened up new possibilities. Today, eggs can be directly removed from a woman's ovaries, and combined with sperm outside of the uterus through a process called in vitro fertilization. The artificially fertilized egg is then put back into the woman's body so that an otherwise normal pregnancy may take place. Though discussion of in vitro fertilization is outside the scope of this document, we mention it because the development of this technology has made it possible for otherwise infertile couples to become pregnant. See our document covering Infertility for further information on this and related infertility topics.