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| |    The Events of Conception by Marjorie Greenfield, M.D. reviewed by Marjorie Greenfield, M.D. Although we all have a pretty good idea of the lovemaking aspects of sexual intercourse, exactly what happens internally to a woman's body after ejaculation may be a bit of a mystery. Here's a primer on how conception actually takes place. The sperm's journey During sexual intercourse, the man's sperm are deposited near the woman's cervix. Within 90 seconds of ejaculation, many sperm have already entered the cervix. If it's around the time of a woman's ovulation, there is a large amount of clear mucus near the cervix that helps make the sperm ready to fertilize the egg. The sperm travel through the uterus, where contractions propel them upwards and out into the fallopian tubes. Sperm can be found in the tubes five minutes after ejaculation. That being said, it is important to note that there are nooks and crannies in the cervix where sperm wait for a bit before traveling to the tubes, and sperm are available to fertilize the egg for two to three days after ejaculation. The egg's journey At ovulation, the follicle pops open and the egg is released. Fingerlike projections at the ends of the tubes (the fimbria) are drawn by chemical attractants to the egg, and pick it up for transport down one of the woman's two fallopian tubes. The egg enters the tube within a few minutes of its release by the ovary. The hormones of the woman's body help the tube contract and push the egg towards the uterus. Little hair-like projections in the tube (cilia) also wave the egg down the tube. The egg waits in the midpoint of the tube for the sperm to arrive. It is ripe for fertilization for about 24 hours. Fertilization When the sperm find the egg, the first one to penetrate the egg creates a barrier to all the other sperm. The cells of the fertilized egg (zygote) begin to multiply, staying clustered together in a ball. This ball of cells, called a blastocyst, slowly makes its way down to the uterus (three or four days after ovulation) and burrows into the uterine wall (five to seven days after ovulation), a process known as implantation. Even before the placenta and umbilical cord are formed, the cells of the developing embryo start getting their nourishment from the mother-to-be's uterine wall. For more on embryonic development, see our articles on the developing fetus.
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