Common Causes of Infertility
Infertility is typically due to medical problems experienced by one or the other partner. In reading about these medical problems (which you will have an opportunity to do in the following sections of this document), it is crucial, that you avoid the temptation of assigning blame to partners experiencing such medical problems. Even though the source of the inability to conceive may lie with a specific partner, it is not his or her "fault." Communicating such blame, either directly or inadvertently, will only compound the negative emotions and stress that typically accompany infertility.
Understanding the causes of infertility requires a brief introduction to the biological aspects of fertility. Fertility involves a complex set of coordinating biological process, all of which must work more or less perfectly, more often than not, in order to avoid infertility.
In the man, hormones that cause sperm to be produced act on the testicles. The testicles must be responsive to such hormones in order to begin or continue sperm production. Similarly, the prostate and other glands must produce seminal fluid that is nourishing and protective of the sperm. In order to send the sperm out of his body, a man must be able to obtain and sustain an erection (hardening of the penis) until he can ejaculate (when sperm mixed with other fluids exit the penis) inside the female. Sperm that is released must be strong enough to swim up the woman's reproductive tract. Along the way, many sperm will die trying to get to the egg, so it is also important that the sperm be numerous enough to allow some survivors after these casualties.
Male-Factor Infertility (or when the problem lies with the male) is most commonly due to low sperm count, defined as less than 20 million sperm per ml. Other causes include varicoceles, which are dilated veins of the spermatic cord (the blood/nutritional supply of the sperm). Varicoceles cause a lack of circulation of the developing sperm that results in a low sperm count. Men can also have damaged or blocked sperm ducts caused by anatomical pressure (e.g., from a varicocele) or scarring from an untreated sexually transmitted disease (most commonly gonorrhea and chlamydia). Hormonal abnormalities that impede the development and maturation of sperm can also cause male-factor infertility. Testicles may also be non-responsive to hormones, and not listen to the signals that turn on sperm development. About 10% of infertile men have antibodies (immune cells that attack other cells) to their own sperm. A woman may also have these antibodies to her partner's sperm.
The female reproductive system also involves a complex set of coordinated biological processes. A woman must produce specific hormones that cause eggs to mature and ovulate. Her ovaries must be healthy and capable of responding appropriately to these hormonal signals. Once an egg is mature enough to leave the ovary it must travel down healthy, unblocked fallopian tubes. The cervical mucous must change consistency to help facilitate the travel of sperm up the reproductive tract to the spot where it will meet the egg. In addition, the woman's uterus must have a good lining and surface for the pregnancy to attach to and start developing. Finally, her body must be able to "recognize" the developing embryo and not reject it as foreign matter.
Female-factor infertility is most commonly caused by lack of ovulation (e.g., the development and release of eggs from the ovary). Ovulation problems can be caused by hormonal deficiencies or lifestyle factors, such as obesity, alcohol intake, or being severely underweight. Fallopian tube blockage is another common cause of infertility. This blockage is most commonly caused by scarring from a previous (often untreated) sexually transmitted disease. Endometriosis (uterine tissue that grows outside the uterus) can also contribute to infertility. In addition, anatomical abnormalities, such as fibroids or scar tissue, can contribute to the inability of sperm to meet the egg or cause the egg to fail to implant in the uterine wall.
Age also impacts women's fertility. Women have more difficulty getting pregnant as they reach "advanced maternal age" (which is currently defined as over age 35), due to a decrease in the number of eggs which ovulate, as well as a decrease in the quality of eggs. Since women are born with all of the eggs that they will ever have, the longer a woman lives, the more likely it is that cell division and exposure to toxins can cause genetic problems within her remaining eggs. Genetic problems are the number one cause of miscarriages, which are described in the next section. Embryos with severe genetic abnormalities are more often miscarried, whereas, embryos with mild genetic disorders (such as Down's Syndrome) often remain in the uterus and grow into babies. This is why women over the age of 35 have a greater risk of having babies with Down's Syndrome and other genetic abnormalities. For this reason, older expectant moms are offered genetic testing. If you are over the age of 35 and want to become pregnant, don't panic. Current data show that many couples are waiting longer to have children, and many of these woman have uncomplicated conceptions, pregnancies, and childbirth.
In addition to male and female-factor infertility, there is also "Unexplained Infertility" which occurs when doctors cannot pinpoint a specific source causing infertility. Not knowing why infertility is occurring adds an additional painful layer of stress onto an already frustrating and confusing condition. The good news is, there are medical treatments for most types of infertility, including those that are 'unexplained.'