25.16 Reproductive technology has benefits and dangers.

A needle penetrates an egg as the DNA from a single sperm is injected into the cytoplasm of the egg.

Many methods exist that help otherwise infertile couples to have children. In this section we examine some of these techniques, beginning with the somewhat low-tech procedure that, more than a hundred years ago, started it all.

In 1884, a woman came to see Dr. William Pancoast because she had not been able to conceive a child. After examining the couple, Dr. Pancoast determined that the husband was infertile. In a discussion about the case with his medical students, someone suggested that semen be collected from “the best-looking” member of the class to inseminate the woman. Dr. Pancoast agreed and arranged to see the patient again, under the pretense of another examination, at which point he injected the semen into the woman’s uterus. Only when it became clear that the woman was pregnant did the doctor inform the husband of what he had done. The husband, however, was happy and requested only that the doctor not tell his wife how she had become pregnant. Eventually, a healthy son was born, the first recorded child born as the result of artificial insemination with a donor’s sperm. From these inauspicious beginnings, there have been tremendous advances in the technologies available to couples experiencing difficulty having children.

Infertility is defined as the inability to get pregnant after one year of trying. It affects approximately 7% of married couples in the United States in any given year. There are many causes of infertility—evenly divided between males and females—including low sperm counts and insufficient sperm motility, Fallopian tube damage or blockage, and ovulation problems. In 10% of cases, no cause can be found.

The reproductive technologies available are varied and include such interventions as surgery to repair blocked Fallopian tubes and hormone treatments to increase sperm counts or egg production. They also include a range of options called assisted reproductive technology (ART), the use of fertility treatments in which both sperm and egg are handled. These procedures typically involve removing eggs from a woman’s ovaries, combining them with sperm to achieve fertilization in a Petri dish, and reinserting the fertilized eggs into the reproductive tract of that woman, or another woman. In many cases, the eggs, sperm, or fertilized eggs may be frozen for some period of time (FIGURE 25-32). The methods used in ART include the following:

Figure 25.32: ART procedures.

1. IVF-ET. This stands for in vitro fertilization–embryo transfer. It is the most common of all ART methods. Several secondary oocytes are collected and combined with sperm in a Petri dish. After several days, the fertilized eggs, at the eight-cell stage, are inserted into the woman’s uterus.

2. ZIFT. Zygote intra-Fallopian transfer differs from IVF-ET in only two respects. After fertilization in a Petri dish, the fertilized eggs are transferred not to the uterus but to one of the Fallopian tubes instead. Also, they are transferred earlier, at the one-cell stage. Perhaps because surgery is needed to place a fertilized egg within the Fallopian tube, ZIFT is used by only 1% of couples seeking ART. In some cases, transfer to the Fallopian tube is not made until the fertilized egg is in the two- to four-cell stage (this is referred to as tubal embryo transfer). Some studies have shown ZIFT to have a higher implantation rate than IVF-ET.

3. GIFT. The method known as gamete intra-Fallopian transfer differs from ZIFT only in that the oocytes are mixed with sperm and immediately transferred to a Fallopian tube, so that fertilization occurs in the body, rather than in a Petri dish.

In some cases, if the male’s sperm counts are particularly low or if his sperm have low motility, a procedure called ICSI, or intracytoplasmic sperm injection, may be used in conjunction with IVF-ET or ZIFT. In this procedure, a single sperm is injected directly into an egg. While this method can be effective as a treatment for male infertility, there are concerns because sperm selection is bypassed. That is, instead of one sperm “winning” the competition to fertilize the egg, a sperm is selected by the individual doing the procedure. This may be why there’s an increased incidence of genetically carried birth defects with ICSI.

Outside the definition of ART is the increasingly effective process for selecting the sex of a baby, known as “sperm sorting.” In this method, a fluorescent dye that binds to the DNA is applied to a sperm sample. Because the X chromosome is larger than the Y chromosome (by about 3%), the X-chromosome-bearing sperm bind more dye. The dyed sperm are then given a small electric charge, positive or negative, depending on which chromosome they carry, and as they are passed through a tube in single file, the sperm cells are deflected to a collecting tube on one side or the other, depending on their charge. The selected sperm carrying an X or Y sex chromosome can then be used in any of the ART methods described above. The purities of the X versus Y samples of sperm range from 70% to 90%.