In vitro fertilization (IVF) is a procedure that aids in the conception of a child. Conception, or fertilization, is the point in reproduction when an egg and sperm combine and an embryo begins to form. An embryo is the earliest stage of human development. IVF is one of a number of treatments called assisted reproductive technology (ART) that was developed in the late 1900’s to treat infertility. Infertility is the inability of a sexually active couple to achieve pregnancy in one year.
During in vitro fertilization, an egg cell is combined with a sperm cell in a laboratory to produce an early embryo. The embryo generated by IVF is allowed to grow in the laboratory for a few days. Then, it is transferred to a woman’s uterus (womb), where it develops until delivery. Embryos produced through IVF can also be frozen for later use. In vitro fertilization has been used for many species of organisms, including humans. Human babies resulting from IVF are sometimes called test tube babies. However, fertilization does not actually take place in a test tube. It occurs in a shallow glass or plastic container called a Petri dish.
Most infertile couples do not require IVF. They can be helped to conceive a child through other methods. But about 3 to 10 percent of infertile couples may need IVF and related treatments (see Infertility ). People may also use IVF in an attempt to avoid transmitting certain inherited diseases from parents to children.
Techniques.
In vitro fertilization requires a number of steps. In order for IVF to work, the woman’s eggs must be mature. The woman takes injections of hormone medications that stimulate her ovaries (egg-producing organs) to produce several mature eggs. The use of medications increases the probability that more than one egg will mature, improving the chances of successful fertilization and pregnancy. During the process, the physician closely monitors the woman, using blood tests and ultrasound examinations to determine the best time for removing the eggs. Ultrasound is the use of high-pitched sound waves to ”see” inside the body.
When the eggs appear mature, a physician performs an egg retrieval. The procedure is done while the woman is sedated (calmed with medication), so that she feels no pain. The procedure involves the use of a special ultrasound probe to which a needle guide is attached. The probe is inserted into the woman’s vagina. A needle is then passed through the needle guide. The needle pierces the vaginal wall to reach the woman’s ovaries and remove the eggs.
After the eggs have been removed, they are taken straight to a laboratory. There, they are placed in a Petri dish containing a nutrient-rich solution. The dish is placed in an incubator, and the eggs are allowed time to adjust to this new environment.
Today, IVF procedures can be carried out using either freshly retrieved eggs or eggs that have been frozen. Scientists have largely overcome the technical problems associated with egg freezing. As a result, IVF procedures using frozen eggs have similar rates of success to those in which freshly retrieved eggs are used. It is also possible for a woman to donate eggs to women who do not generate mature eggs or are unable to get pregnant with their own eggs.
Around the same time that the eggs are collected, a sperm specimen is collected from the male partner or a sperm donor. If donor sperm is used, the specimen must be frozen for six months to make sure it is free of transmissible diseases. The donor is tested for various diseases prior to donation and again after six months. The donor must be disease free at both test times before the sperm can be used.
The sperm must be specially treated by washing and incubation before it can be used. A small amount of sperm is then placed together with the eggs and left for about 18 hours. In cases of severe male infertility, doctors may use a special microscope and a microscopic needle to inject a single sperm into each mature egg. This procedure is called intra-cytoplasmic sperm injection (ICSI). Following either procedure, the eggs are examined to see if fertilization has occurred. If it has, the fertilized eggs are returned to the incubator.
Following fertilization, embryos are allowed to develop in the laboratory for two to seven days. Embryos may be frozen for later use or transferred to the woman’s uterus. In order to transfer an embryo to the uterus, a physician places an extremely thin tube containing one or more embryos through the cervix (opening of the uterus) and into the uterus. This largely painless procedure requires no anesthetic. To minimize the risk of multiple pregnancy, physicians transfer as few embryos as needed to achieve a pregnancy. Any surplus embryos can be frozen for future use.
Couples can also use IVF to avoid transmitting genetic diseases to their offspring. Such diseases include sickle cell anemia and cystic fibrosis . The egg retrieval process is the same, except that an additional procedure is performed before the embryos are transferred to the woman. This procedure is called pre-implantation genetic testing (PGT). With PGT, a special microscope and microscopic surgical tools are used to obtain cells from an embryo. The cells are taken five to seven days after fertilization, when the embryo has developed into a blastocyst. A blastocyst is the first stage of differentiation. Differentiation is the process by which a cell changes from one cell type to another during human development. The blastocyst is made up of two distinct parts: One part develops into the placenta, and the other, into the fetus. The placenta provides the unborn baby with food and oxygen and carries away the baby’s waste products. Fetus is the term used for an embryo after about two months of development. The cells removed from the embryo come from the part that becomes the placenta. These cells are tested to determine if they carry genes known to cause a genetic disease. Only embryos that are incapable of causing the disease are transferred to the uterus.
Rate of success.
The success of in vitro fertilization depends largely on the age of the female and the quality of the eggs that the ovaries mature. According to the United States Centers for Disease Control and Prevention (CDC), women under the age of 35 can expect about a 40 percent likelihood of pregnancy following one IVF procedure. Women between ages 40 and 42 have less than a 20 percent likelihood of pregnancy after one procedure. And women 45 years or older have less than a 2 percent likelihood of having a baby following a single IVF procedure.
Multiple birth is the most common risk of IVF pregnancies. Multiple birth means having more than one infant during a single pregnancy. In the United States, about 18 percent of IVF pregnancies are multiple pregnancies. Multiple-birth pregnancies are far more likely to result in premature birth, low birth weight, and infant disability or death than single-birth pregnancies are. Such serious complications also affect single-birth IVF pregnancies at a slightly higher rate than naturally conceived single-birth pregnancies.
Ethical concerns.
The development of IVF has led to a number of ethical (moral) concerns. For example, some people believe that the fertilization of the egg is the beginning of life. They might thus object to freezing embryos, because some embryos may die in the process. Other people are concerned about what may happen to embryos that a couple never uses. Still others object to IVF because of their religious beliefs. In 1987, the Roman Catholic Church issued a statement opposing the use of in vitro fertilization. However, not all religions oppose the use of IVF.
History.
Scientists made the first attempt to fertilize mammals’ eggs in the laboratory in the late 1800’s. By the mid-1900’s, they had succeeded. In 1971, a British team of two doctors, Robert Edwards and Patrick Steptoe, and a nurse, Jean Purdy, reported the first account of a human blastocyst that had been formed in a glass dish. Purdy was the first person to recognize and describe the formation of a human blastocyst. Seven years later, Edwards and Steptoe, along with Purdy, achieved the world’s first human IVF birth. The first IVF baby, Louise Brown, was born in Oldham, England, in 1978. In 2010, Edwards, the only surviving member of this pioneering team, won the Nobel Prize in Physiology and Medicine for developing IVF. Today, IVF deliveries account for about 1 percent of all babies born annually in the United States.
In the 2010’s, scientists developed a controversial IVF technique that involves the transfer of a cell nucleus. The nucleus is the part of a cell that contains nearly all its genetic material. The technique involves transferring the nucleus from the egg of one woman to the egg of another woman that has had its own nucleus removed. The newly formed egg is then fertilized with sperm from a donor. The resulting embryo gets most of its genetic material from the donors of the sperm and of the egg nucleus. Its mitochondria, however, come from the donor of the egg to which the nucleus is transferred. Mitochondria are the parts of a cell that produce energy. Mitochondria have their own genetic material and are found outside the nucleus. This three-donor procedure may help women with inheritable diseases of the mitochondria to conceive healthy children.
See also Edwards, Robert Geoffrey ; Fertilization ; Reproduction, Human ; Surrogate birth .
