Human beings are remarkably fertile. Most females are capable of conceiving and bearing children beginning in their mid-teen years. While women in industrialized societies usually bear children in their 20s and 30s, women can give birth well into their 40s and beyond. Men can be fertile into extreme old age. Unlike most mammals, humans can mate successfully year round; fertility is not restricted to a particular season of the year or to brief episodes of female heat.
But the process of reproduction is immensely complex. For conception to take place and pregnancy to begin, hundreds of individual hormonal, chemical, and physical events must take place in a precise order. For example, a sperm must form in the testicle, mature in the epididymis, be released into the female vagina, "swim" through the cervical opening, continue through the uterus and into a fallopian tube. In the tube, it must encounter a viable egg within 12 hours or so of its monthly release, attach itself to the egg, penetrate its outer vestments and fertilize the ovum within. After staying in the fallopian tube for about two days, the fertilized egg must descend into the uterus, grow and divide for a few more days, and then implant itself on the uterine wall.
A single disruption, small or large, in any of these events and conditions can cause infertility. The sperm may not be viable it may be dead, it may contain the wrong number of chromosomes, it may have been stored too long after its formation. Or it may be viable but immotile, meaning that it cannot "swim" correctly. It may be perfectly healthy but not accompanied by enough other sperm, for although only one sperm is ultimately required for fertilization, men whose semen contains less that 20 million sperm per milliliter frequently have infertility problems. The sperm ducts may be blocked, because of past infection or injury. The man may not be able to ejaculate, or his ejaculation may propel the sperm backward into his bladder rather than out through the penis. Once inside the cervix, the sperm may meet mechanical or chemical roadblocks. A muscle spasm may eject the sperm, the cervical mucus may be too thick to penetrate, or chemically hostile to the sperm. The fallopian tube may be blocked by scar tissue. If the sperm does manage to reach the egg, it may not be able to penetrate its defenses to fertilize it. A fertilized egg may become stuck in the fallopian tube. Or it may not be able to implant successfully in the uterus.
In the late 20th century, medical science has made great advances in understanding each stage of the reproductive process and in identifying the problems that can occur at each step. In an increasing number of cases these barriers can be corrected or worked around in order to achieve fertility for about 65% of couples who seek the help of fertility specialists. Although most of the biological work of creating children must still be done by the human body—the gestation bottles depicted in Aldous Huxley's 1946 novel Brave New World are still impossible—science can provide substitutes for a few key processes.
Is infertility becoming more common? Despite public worry and discussion, the actual incidence of infertility has remained fairly stable over the years. One American couple out of 5 or 6 currently experiences infertility. Infertility grows more common with increasing age; about 33% of couples in their late 30s are infertile. The age factor has taken on new importance as many people in the United States and similar industrialized countries have put off marriage and children until certain educational or career goals are reached. For some time during the "sexual revolution" of the 1960s and '70s, doctors did see higher incidence of infertility caused by tubal blockages left by untreated venereal diseases such as gonorrhea and chlamydia. But this trend seems to have reversed since the appearance of AIDS has forced the adoption of barrier methods of contraception, which prevent most venereal diseases. Another social factor, the increasing difficulty of adoption (a result of improved birth control and the availability of legal abortion) has increased the demand for medical answers to infertility, regardless of their complexity and high cost.
Even the most fertile human couple does not necessarily conceive the first time sexual intercourse takes place. In fact, the chance of conception in any given month among fertile couples attempting to conceive is about 20%, or one chance in five. To avoid unnecessary testing and treatment, most doctors will not make the diagnosis of infertility until one year of unprotected intercourse has failed to result in pregnancy. Some cases, involving older couples or existing evidence from previous marriages, may be diagnosed sooner and treated more aggressively.
Once the diagnosis is made, examinations, testing and history-taking begin to find the cause(s) of infertility. In about 30% of infertility cases, the problem can be found solely in a medical problem of the woman's; in another 30%, male factors alone cause the infertility; and in another 30% of cases, both partners have conditions which render the couple infertile. In the remaining 10% of cases, no clear cause can be found.
Women are given a physical and pelvic examination, laboratory tests, and one or more imaging procedures to locate the problem which may be causing infertility. Testing may include exploratory surgery, using laparoscopy. In this technique, a small fiber-optic tool is inserted through a "keyhole" incision to allow the physician to inspect the reproductive system. Advanced ultrasound imaging may also reveal structural or functional problems. One commonly found condition during the infertility evaluation is endometriosis. In this disorder, cells from the endometrium, which normally line the uterus, spread in patches and cysts throughout the female reproductive system. Additionally, some women do not ovulate regularly or at all. Others may produce eggs regularly that are prevented from being fertilized, descending or implanting.
Men are tested for the presence, quantity and quality of their sperm. The most common problem affecting male sperm levels is a varicocele, a tangle of veins surrounding the testicle. Surgical correction of large varicoceles restores fertility in about two-thirds of cases. Other causes of male infertility include insufficient hormone levels (which may be supplemented); blocked tubes which carry sperm (which can sometimes be surgically repaired or bypassed), untreated diabetes or prostate disease and other conditions.
After testing is complete, doctors devise a strategy for each couple to increase fertility. The optimum treatment is one that allows existing natural processes to take place. Sometimes, very small adjustments in sexual frequency and timing may result in pregnancy. Patients are taught to identify the woman's most fertile times so that intercourse can take place. Practices that temporarily result in lowered sperm counts or abnormally formed sperm, including the use of certain medications, alcohol, marijuana, and hot tubs or saunas—can be curtailed.
If the problem is insufficient sperm, a sperm sample can be concentrated by centrifuging, chemical treatment, or other procedures to be more potent. Following such adjustments, the sperm can be introduced into the woman's body. Lack of ovulation can be treated with hormones and chemicals to produce "superovulation," which can be followed by normal intercourse, artificial insemination or other ways of bring sperm and egg together.
Once thought radical and futuristic but now considered quite routine, the best-known medical "fix" for infertility is in vitro fertilization. "In vitro" means "in glass," and it involves the mixing of sperm and egg in the laboratory, outside the human body. After fertilization takes place, the zygote (fertilized egg) may be surgically placed in the woman's fallopian tube. Alternatively, it may be allowed to develop further outside the body and then be introduced into the uterus in an effort to establish a pregnancy.
One of the most recent developments in ART (assisted reproductive technology) is intracytoplasmic sperm injection, (ICSI). This microsurgical procedure involves injecting a single sperm into an egg, allowing men with extremely low sperm counts to become fathers. Further advances in ART are expected from the quickly evolving fields of genetics, imaging, and biotechnology.
The rapid development of new medical technology has raised many ethical and legal issues. Society is only beginning to devise acceptable answers.
Philosophers and theologians ask whether humans have the right to tamper with natural processes.
Practitioners and their patients have more immediate concerns—what shall be done with "extra" eggs, sperm, and zygotes? Must they be kept frozen indefinitely? At whose expense? Who "owns" them if the parents divorce or die?
New reproductive technologies are changing many cherished ideas about family relationships. Today a child can be born from a donated egg, with donated sperm, from the uterus of a woman who is a "gestational carrier." In this way, a woman with no hereditary link to the offspring may deliver a child who is also not related by genetics to the eventual parents of the child. When all parties agree to such unconventional arrangements, they can be quite satisfactory. But when disagreements arise, the legal issues involved are formidable.
Another issue involves the identification and selection of "the best" sperm, egg or embryo. Many people wonder about the moral effect on our society of any attempt to prevent all children with defects from being born.
When fertility treatment results in multiple pregnancies, couples face an ethical dilemma. While it is possible to selectively abort one or more embryos to improve the chances of the others survival and to reduce the burden on parents of raising quintuplets or sextuplets, this is a difficult decision for couples. Is this a justifiable act? Does this differ substantially form abortion as traditionally practiced?
Others question the wisdom of spending many thousands of scarce medical care dollars to give an affluent couple a baby of their own biological parentage, when millions of existing children around the world are parentless. Healthcare policy makers debate whether infertility treatment is a basic right that should be paid for by medical insurance, or an elective luxury, similar to cosmetic surgery, available only to those who can afford it.
Because infertility and its treatment raise all these issues, and because the treatment itself may involve considerable time, expense, and loss of privacy, many couples find the procedure extremely stressful. Physicians experienced in the field recommend both private counseling and infertility support groups to assist couples in their journey through the process.