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The seminal fluid (semen) itself is analysed for abnormalities. Most men ejaculate 2.5 to 5 cc (1/2 to 1 teaspoon) of semen. Amounts greater than 1 cc but lower than 2.5 cc may indicate prostate problems or frequent intercourse. A semen sample that is less than 1 cc could indicate a blockage of the ejaculatory ducts or other tubular abnormalities. No ejaculate at all may signal retrograde ejaculation. High amounts of ejaculate may, in some cases, also contribute to infertility. Normal semen is liquefied within 20 minutes by certain enzymes, if it remains sticky, however, fertility may be impaired. An absence of fructose (sugar) and sperm indicates that an obstruction has occurred either in the vas deferens or the epididymis, since fructose is added to the semen in the epididymis. Conversely, if there is fructose in the semen but no sperm, then the channel from the epididymis is open but there is a defect in sperm production. Infections may be detected. Low levels of a substance called inhibin B, which appears to be produced only in the testes, may indicate blockage or abnormalities in the seminiferous tubules. Similarly, low levels of another compound, alpha–glucosidase, indicate blockage in the epididymis.
The hamster test, or micro–penetration assay test, uses the sperm sample to fertilise hamster eggs that have had their covering removed to allow penetration. If less than 5% to 20% of the eggs are fertilized, infertility is diagnosed. This test is not used often, it is very expensive, does not test the ability of the sperm to penetrate the egg’s covering, may lead to an incorrect diagnosis of infertility, and so may be no more useful than less expensive semen analyses. A newer procedure, the human zona penetration test, uses sperm to fertilize dead human eggs, which are usually obtained from an ovary that was removed for medical purposes. (Like the hamster test, the procedure cannot result in a living embryo.) Researchers hope it will provide the same information as the hamster test and also indicate whether the sperm can penetrate the outer coating of an egg.
The postcoital, also known as Simms–Huhner, test is designed to evaluate the effect of a woman’s cervical mucus on a man’s sperm. To perform this test, a woman is asked to come into the physician’s office within two to 24 hours after intercourse at mid–cycle (when ovulation should occur). A small sample of cervical mucus is obtained and examined under a microscope. A problem is detected if the physician observes no surviving sperm or no sperm at all. If results are poor, the woman’s cervical mucus should also be cultured for the presence of infection. The test can indicate that a problem exists but cannot determine its cause in most cases. The test also cannot evaluate sperm movement from the cervix into the fallopian tubes or the sperm’s ability to fertilize an egg.
The swim–up test may prove to be a good method for testing the ability of sperm to escape from the semen into the cervical mucus. A specially prepared semen sample is placed in a tube. A culture media (a substance in which organisms can multiply) is placed on top of the sample. The medium is a hospitable environment for sperm, and those that are healthy will swim up to it. After an hour or more, the culture is examined, and the number of sperm that have reached the medium is compared to the number still remaining in the semen. The result gives a fair estimation of the number of sperm potentially capable of fertilization. The swim–up test has the added advantage of providing healthy sperm for intra–uterine insemination and assisted reproductive techniques.
If sperm counts are low, blood tests may be taken to determine levels of the hormones FSH, LH, and testosterone. Normal results, however, do not ensure fertility. For example, germ cells may produce adequate amounts of sperm in response to normal hormone levels, but there may be a defect in sperm maturation or a blockage in the sperm transport system that does not depend on hormones but does reduce the final sperm count. Usually, only if the testicles are very defective will FSH hormone levels rise abnormally.
If a man has had a vasectomy reversed and still cannot conceive or if semen analysis shows sperm clumping together, blood tests for anti–sperm antibodies will be conducted. The primary negative effect of these antibodies is to bind the sperm to the woman’s cervical mucus, preventing the sperm from swimming further up.