In vitro fertilization (IVF), with subsequent embryo transfer, involves the fertilization of eggs by sperm in a test tubeÑin vitroÑrather than in the body. It is used as a treatment for some types of infertility. The technique involves removal of the eggs from the ovary prior to ovulation, collection of a sperm specimen, and mixing the gametes in specially prepared growth media to allow the process of fertilization to occur. The fertilized eggs are then placed in the uterus to establish a pregnancy and complete their maturational development. This technique has contributed significantly to understanding the mechanism of fertilization and early embryonic development, as well as providing many couples with a baby.
IVF was originally tested successfully in animals and was subsequently modified and attempted in humans in the 1970s. The first report of the birth of a baby via IVF and embryo transfer came from England in 1978, by a group led by Drs. Patrick Steptoe and Robert G. Edwards.
The technique was originally introduced as a treatment for mechanical infertility, to bypass blocked or absent fallopian tubes. The encouraging results in women with this condition prompted the use of IVF for couples whose infertility was the result of other conditions not necessarily related to fallopian tube malfunctionÑfor example, poor sperm quality, the presence of antibodies to sperm, and endometriosis.
IVF treatment starts with drug therapy, to induce the ovary to develop multiple eggs, in contrast to the single egg that develops in the natural cycle. Multiple eggs will result in multiple embryos and offer a higher chance of success. The response to therapy is monitored closely until the eggs reach developmental maturity. The eggs are then harvested by needle aspiration and put into specialized growth media. Sperm is collected, added to the eggs, and the mixture is placed in an incubator under a controlled atmosphere. Fertilization is usually evident after 24 hours, and by 48 hours the embryos are ready to be inserted into the uterus through the cervical canal. Pregnancy can usually be detected 10 to 14 days later. A standard cycle of IVF usually results in the development of multiple embryos.
However, it is undesirable to place more than four embryos into the uterus at one time, due to the high risk of multiple pregnancy. The unused embryos can be frozen and stored in liquid nitrogen, to be thawed and used at a future date.
Despite the enthusiasm and improvements in technology, the success of IVF and related techniques continues to be modest, with approximately 20-percent incidence of full-term pregnancy. This has prompted investigators to search for alternatives that attempt to minimize the exposure of the egg, sperm, or embryo to the artificial environment. In gamete intrafallopian transfer (GIFT), the egg and the sperm are mixed and placed directly into the fallopian tube and not in vitro. The tubal embryo transfer (TET) technique combines IVF and GIFT. The eggs and the sperm are mixed in vitro, but the fertilized egg is placed into the fallopian tube and not into the uterus as in standard IVF. The transfer in both GIFT and TET is usually performed surgically through a small incision in the abdominal wall (laparoscopy). Definitive proof is still lacking for claims of higher success rates with GIFT and TET, over standard IVF. Researchers are focusing on two problems: embryos that may be abnormal and less-receptive endometria, both related to the aging uterus and ovaries. Development of genetic testing for embryos, not yet done routinely in humans, will help.
The successes of IVF and embryo freezing technology have raised some unusual legal and ethical issues, including what to do with frozen embryos if the parents die and custody of the embryos in case of a divorce. The Vatican issues a statement in 1987 condemning IVF, surrogate motherhood, and other practices involving embryos.