Science Fair Project Encyclopedia
In vitro fertilisation
In vitro fertilization(AE) or fertilisation(BE) (IVF) is a technique in which egg cells are fertilized outside the woman's body. It is a major treatment in infertility. In brief, the process involves controlling the ovulatory process, removing ova (eggs) from the woman's body and letting sperm fertilize them in a fluid medium. The fertilized egg or embryo is then transferred to the patient's uterus with the intent to establish a successful pregnancy. "In vitro" is Latin for "in glass", referring to the test tubes, however neither glass nor test tubes are being used.
The technique was developed in the United Kingdom by Doctors Patrick Steptoe and Robert Edwards. The first so-called "test-tube baby", Louise Brown, was born as a result on July 25, 1978 amid intense controversy over the safety and morality of the procedure.
The first successful IVF treatment in the USA (producing Elizabeth Carr) took place in 1981. Since then IVF has exploded in popularity, with as many as 1% of all births now being conceived in-vitro, with over 115,000 born in the USA to date.
Initially the IVF was developed to overcome infertility due to problems of the fallopian tubes, but it turned out that it was successful in most infertility situations. The introduction of ICSI (see below) addresses the problem of male infertility to a large extent. Thus for IVF to be successful it may be easier to say that it requires healthy ova, sperm that can fertilize, and a uterus that can maintain a pregnancy. Cost considerations generally place IVF as a treatment when other, less costly reasonable options have failed.
Treatment cycles are typically started on the third day of menses and consist of a regimen of fertility medications to stimulate the development of multiple follicles of the ovaries. In most patients injectable gonadotropins (using FSH such as Pergonal) are used under close monitoring. Such monitoring checks frequently the estradiol level and, by means of gynecologic ultrasonography, follicular growth. Typically approximately 10 days of injections will be necessary. Endogenous ovulation is blocked by the use of GnRH agonists or GnRH antagonists.
When follicular maturation is judged to be adequate, hCG is given. This agent would lead to ovulation about 42 hours after injection, but just before that time a retrieval procedure will take place to recover the egg cells from the ovary. The eggs are retrieved from the patient using a transvaginal technique involving an ultrasound-guided needle piercing the vaginal wall to reach the ovaries. Through this needle follicles can be aspirated, and the follicular fluid is handed to the IVF laboratory to identify ova. The retrieval procedure takes about 20 minutes and is usually done under conscious sedation or deeper anesthesia.
In the laboratory, the identified eggs are stripped of surrounding cells and prepared for fertilization. In the meantime, semen is provided by the male partner and prepared for fertilization removing inactive cells and seminal fluid. The sperm and the egg are incubated together (at a ratio of about 75,000:1) in the culture media for about 18 hours. By that time fertilization should have taken place and the fertilized egg would show two pronuclei . In situations where the sperm count is low a single sperm is injected directly into the egg using intracytoplasmic sperm injection (ICSI) (see below). The fertilized egg is passed to a special growth medium and left for about 48 hours until the egg has reached the 6-8 cell stage.
Laboratories have developed grading methods to judge oocyte and embryo quality. Typically, embryos at the 6-8 cells stage are transferred three days after retrieval, however in many programs, especially if many day-3 embryos are available, embryos are placed into an extended culture system with a transfer done at the blastocyst stage. Blastocysts tend to give higher pregnancy rates.
The embryos judged to be the "best" are transferred to the patient's uterus through a thin, plastic catheter, which passes through her vagina and cervix. Often, several embryos are passed into the uterus to improve chances of implantation and pregnancy.
The patient has to wait two weeks before she returns to the clinic for the pregnancy test. During this time she may receive progesterone - a hormone that keeps the uterus lining thickened and suitable for implantation. Many IVF programs provide additional medications as part of their protocol.
The chances of a successful pregnancy is approximately 20-30 per cent for each IVF cycle. There are many factors that determine success rates including the age of the patient, the quality of the eggs and sperm, the duration of the infertility, the health of the uterus, and the medical expertise. It is a common practice for IVF programs to boost the pregnancy rate by placing multiple embryos during embryo transfer. IVF programs generally publish their pregnancy rates, however comparisons between clinics are difficult as many variables determine outcome.
The major complication of IVF is the development of multiple births. This is directly related to the practice of placing multiple embryos at embryo transfer. Spontaneous splitting of embryos in the womb after transfer does occur, but is rare (<1%) and would lead to fraternal twins. Another major complication, related to the use of ovarian stimulation is the development of the ovarian hyperstimulation syndrome. Birth defects appear not significantly increased in IVF, however, may be increased in cases where ICSI is utilized. In the latter situation it needs to be taken into account that men with significant sperm problems are at higher risk for genetic abnormalities, thus it remains to be seen if a possible increase in birth defects in offspring of couples where ICSI is used is not just a reflection of a higher genetic burden.
If multiple embryos are generated, patients may choose to freeze embryos that are not transferred. Those embryos are placed in liquid nitrogen and can be preserved for a long time. The advantage is that patients who fail to conceive may become pregnant using such embryos without having to go through a full IVF cycle. Or, if pregnancy occurred, they could return later for another pregnancy.
Cryopreservation of unfertilized mature oocytes has been sucessfully accomplished.
Ovarian tissue cryopreservation
Cryopreservation of ovarian tissue is of interest to women who want to preserve their reproductive function beyond the natural limit, or whose reproductive potential is threatened by cancer therapy. Research is trying to address this issue.
Intracytoplasmic sperm injection (ICSI) is a more recent development associated with IVF which allows the sperm to be directly injected in to the egg uysing micromanipulation . This is used for sperm that have difficulty the egg and when sperm numbers are very low. ICSI results in success rates equal to IVF fertilization.
Certain ethical issues have been raised from the beginning when IVF was introduced. Theses concerns include:
- Bypassing the natural method of conception.
- Creating life in the laboratory.
- Fertilizing more embryos than will be needed.
- Discarding excess embryos.
- Unnatural environment for embryos.
- Using untested technology.
- Not affordable for many.
- Disallocation of medical resources.
- Contributes to overpopulation.
- Creating embryos, freezing them, and keeping them "in limbo".
- Exposing embryos to unnatural substances.
- Destroying embryos in research.
- Potential to create embryos for medical purposes.
- Potential to select embryos (PGD).
- Potential to modify embryos.
Separating the traditional mother-father model
The IVF process requires sperm, eggs, and a uterus. To achieve a pregnancy any of these requirements can be provided by a third party (or more parties): third party reproduction. This has created additional ethical and legal concerns. The use of IVF provides also greater range of options for single people and same-sex couples wishing to have children. Although both groups already raise children, IVF facilitates this process. Some people object that this could give psychological problems to the child if they grow up without a mother/father role-model.
A number of cases have achieved notoriety:
- In 2001, a French woman received worldwide publicity when she posed as the wife of her brother in order to give birth to a donor egg fertilized by his sperm. Some saw this as a form of incest; others thought it would prove psychologically unhealthy for the child when he learned how he was delivered; whereas other people simply couldn't see anything wrong with the situation.
- In a few cases laboratory mix-ups (misidentified gametes, transfer of wrong embryos) have occurred leading inadvertent third part reproduction. This led to complex paternity issues and legal action.
Pregnancy past menopause
While menopause has set a natural barrier to further conception, IVF has allowed women to be pregnant in their fifties and sixties. These women whose uterus has been appropriately prepared receive embryos that originated from an egg of an egg donor. Therefore, their children are not genetically linked to them. Even after menopause the uterus is fully capable to carry out its function. Currently, the oldest women to give birth is Adriana Iliescu, age 66, from Romania.
While in the United States IVF programs operate under voluntary guidelines, programs in many other countries are subject to regulations that regulate many aspects of IVF practice. In such settings regulations may dictate:
- The number of oocytes that can be fertilized.
- The number of embryos that can be transferred.
- The use of cryopreservation.
- The use of third party reproduction.
- The ability to perform tests or interventions on the embryo.
- Steptoe, P. C., and Edwards, R. G. (1978) death after the reimplantation of a human embryo. Lancet. 2: 366
- Porcu E, Fabbri R, Damiano G, Fratto R, Giunchi S, Venturoli S.: Oocyte cryopreservation in oncological patients. Eur J Obstet Gynecol Reprod Biol. 2004 Apr 5;113 Suppl 1:S14-6. PMID 15041124.
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