In Vitro Fertilization
When performed by an experienced practitioner and in an experienced clinic, IVF generally results in pregnancy rates of about 28 percent after one attempt and 51 percent after three. One study has reported the pregnancy rate after six attempts as being 56 percent. Another has reported it as being 66 percent.
Generally, one attempt at IVF is made per menstrual cycle. The IVF process begins when couples are first screened. Clinicians first must rule out infertility in the male partner. If the problem is with the female partner, various courses of treatment may be available. Generally, couples are expected to try to achieve pregnancy for a year after the initial screening before intervention is attempted. However, if a woman is in her late thirties or older, or if she is experiencing irregular menstruation, a clinical investigation may begin earlier.
Especially in older women, the blood level of follicle-stimulating hormone, a hormone that acts on the ovary to stimulate the maturation of viable eggs, is measured. If the hormone's level is found to be elevated early in a woman's menstrual cycle (after the first week of the new cycle), her ovaries may not be responding to it. In that case, hormonal treatment to stimulate ovulation would be ineffective, and assisted reproductive technology would be unable to help achieve pregnancy. Elevated estrogen levels at day three would also indicate that the ovaries are not responding correctly to estrogen or hormones.
In women whose ovaries are capable of generating viable eggs, the first step in IVF is referred to as "superovulation." To increase the chance of success, the woman's ovaries are stimulated to develop many follicles. Normally, only one or perhaps two follicles develop and are released by an ovary during a single menstrual cycle, which is why usually only one or, on rare occasions, two children are born. In superovulation, a doctor forces multiple follicles to develop so that many oocytes can be collected.
To stimulate the ovaries to develop many follicles, the woman undergoes the "long protocol." The action of the pituitary gland is suppressed hormonally, and ten days later the woman is treated with follicle-stimulating hormone. To see how well her ovaries are responding to the hormone, doctors measure estrogen blood levels and observe the ovaries with ultrasound scans. The number and size of the follicles can be visualized. When the doctors judge that the time is right (that is, when the follicle is enlarged to the point that it protrudes above the surface of the ovary), they give the woman human chorionic gonadotropin, wait thirty-six hours, and collect the oocytes from the mature follicles.
In the past, to collect follicles, doctors performed laparoscopy, in which a thin optical tube with a light (called a laproscope) is inserted through a very small incision in the abdominal wall, and the pelvic organs are viewed with fiber optics. Today, the use of a needle guided by ultrasound makes the procedure much faster. The ovary is visualized, mature follicles are located, the needle is inserted, and the follicular fluid that contains the mature oocyte (the unreleased egg) is aspirated. The doctors may collect up to eleven oocytes from a single patient.
Viable sperm are collected from the man and washed in a special solution that activates them so they can fertilize the egg. The process of sperm activation is called "capacitation" and normally occurs when sperm are ejaculated and enter the female reproductive tract. Capacitation involves activating enzymes in the sperm's acrosomal cap, allowing the sperm head, which contains the sperm's genetic material, to penetrate the outer and inner membranes of the egg (zona pellucida and vitelline membrane). For males with azoospermia, microsurgical or aspiration techniques can directly extract sperm from either the epididymis or the testicles. Azoospermia is the most severe form of male infertility, caused by obstructions in the genital tract or by testicular failure.
To allow fertilization to take place, a single egg and about 100,000 sperm are placed together in special culture medium and incubated for about twenty-four hours. Doctors then use a microscope to see if there are two pronuclei (one from the egg and one from the sperm) in the egg, indicating that fertilization occurred. In some cases, the sperm are unable to penetrate the egg. They may be unable to swim correctly, or they may not have been capacitated successfully. In the past, the only solution was to use sperm from another man. Now, however, sperm can be injected directly into the egg's cytoplasm, in a process called microassisted fertilization.
There are three ways used successfully by doctors and researchers to micro-fertilize the egg. The first is "zona drilling," in which a hole is punched into the zona pellucida, letting sperm penetrate the egg. The second method is called "subzonal sperm insertion," in which a sperm is injected directly under the zona pellucida. A third, related method is "intracytoplasmic sperm injection," in which a sperm is injected directly into the egg cytoplasm. The second method is reported to have a higher fertilization success rate (59%) than the third (13%).
- Reproductive Technology - The Risks Of Ivf
- Reproductive Technology - Pregnancy And Infertility
- Other Free Encyclopedias
Medicine EncyclopediaGenetics in Medicine - Part 4Reproductive Technology - Pregnancy And Infertility, In Vitro Fertilization, The Risks Of Ivf, Embryo Transfer Techniques, Gamete Intrafallopian Transfer