The testicles of adult men produce about half a billion sperm each day. By contrast, a woman's ovaries are stimulated to grow only a few eggs each month. Usually, only one of these eggs reaches maturity and is able to be fertilized.
Fertilization can only occur during ovulation: the time in a woman's monthly cycle where the mature egg is released from the ovary and travels through the fallopian tube. For conception to occur, one sperm must fertilize the mature egg while in the fallopian tube. The fertilized egg must then implant in the uterus, thereby creating an embryo.
Infertility is defined as the inability to naturally produce an embryo despite trying to conceive for at least 1 year. This condition can be caused by both male and female factors.
In vitro fertilization, or IVF, is a highly sophisticated technique used to assist infertile couples in achieving pregnancy. In a typical IVF procedure, a woman is first treated with fertility drugs to stimulate the production of numerous mature eggs. Once these eggs have matured, a needle is inserted through the vagina to remove the eggs. The eggs are then placed in a specially prepared laboratory dish.
After a process called sperm washing, sperm are mixed with the retrieved eggs. This can be achieved by using another needle to inject the sperm into the nucleus of an egg. Or the sperm can be placed with the eggs in the special laboratory dish. A sign that fertilization has occurred is when the eggs begin to cleave, or divide, into multiple cells. Embryos need to be placed in the uterus, approximately 72 hours after fertilization.
For the embryo transfer procedure, a flexible tube, called a catheter, is inserted into the vagina, through the cervix and into the uterus. The embryos are placed in the uterus via the catheter. Additional medications may be given to improve the likelihood of the embryos implanting in the uterus. In order to increase the chance for a successful pregnancy, more than one embryo is usually transferred. This can sometimes result in multiple births.