If you are having trouble getting a woman pregnant after a year of unprotected sex, it may be a good idea to consult a doctor. At that point, you’ll likely be given a semen analysis, also known as a sperm test.
Optimally, the man produces semen by masturbation in a private room in the analysis laboratory, but if that is not possible, a man may bring in semen collected at home. Because men with low numbers of sperm may deplete their sperm reserve by ejaculating too frequently, it is best for a man to wait two to three days after his last ejaculation before he performs a semen analysis.
While the semen analysis is the most commonly used initial test for male fertility, it is unfortunately not very accurate. Many men with a “normal” semen analysis by the numbers have problems conceiving children and, not infrequently, men with an abnormal semen analysis successfully impregnate their partners.
The semen analysis measures average aspects of sperm, whereas male fertility is characterized not by the average, but the most exceptional sperm. The most exceptional sperm travels through the entire female reproductive tract, penetrates and fertilizes the egg, and no test currently exists that can characterize this extraordinary sperm.
As the exceptional sperm is more likely found in a larger number of good sperm, the better the results of the semen analysis, the better a man’s chances, and the shorter time it should take to impregnate his partner. Because a better initial screening test for male fertility is not yet available, doctors currently use the semen analysis to assess the chance a man is likely contributing to a couple’s difficulty conceiving children.
The semen analysis varies widely from sample to sample, and throughout the year. Typically, a doctor requests that a man obtain two semen analyses to judge that patient’s fertility. The semen analysis itself is a complex test, performed by a specially trained technician. Semen analyses may vary substantially among laboratories.
The World Health Organization (WHO) publishes the criteria most widely used for semen analysis, now in its fifth edition. The values in the WHO criteria are designed to identify infertile men, but many men with infertility have values above these numbers. In other words, being above the reference value does not guarantee fertility, or a medical condition that may be treated to improve fertility. The main parts of the semen analysis include:
|Semen analysis part||Reference value for WHO Criteria for Infertile Men|
|Volume||Less than 2.0 ml|
|pH||Less than 7.2|
|Sperm concentration||Less than 20 million sperm per ml|
|Total sperm number||Less than 40 million sperm per ejaculate|
|Motility||Less than 50% with progressive motility|
|Vitality||Less than 75% live|
|White blood cells||More than 1 million per ml|
Morphology: The Shape of the Sperm
In general, sperm vary in shape even in fertile men. According to the fairly loose WHO criteria, the semen analysis is normal if 30% of sperm look normal. In an attempt to make morphology a more precise measurement, “strict criteria” were devised. Although the number may vary, laboratories often use 4% as the cutoff for strict morphology. That means if up to 95% of sperm are oddly shaped by strict criteria, the semen analysis is considered normal.
Scientific studies do not agree on the ability of strict morphology to predict sperm function, and even highly trained laboratory personnel may disagree on how many sperm are normal by strict morphology in a single sperm sample. As a result, a strict morphology result may or may not be meaningful in assessing a man’s fertility. Two good rules of thumb are:
- If all of the sperm are abnormally shaped in the same way (for example, they all have perfectly round instead of oval heads) there’s a problem.
- If the abnormal shape is associated with an identified condition, such as a varicocele (varicose veins in the scrotum), the condition is likely a problem.
Sperm are typically protected from the body’s immune system by specialized bridges between Sertoli cells. If that blood-testis barrier is broken, a man’s body may begin to attack his own sperm. Conditions that may break the blood-testis barrier include injury to the testis, the testis twisting on itself, undescended testes in childhood, vasectomy, and infection. Antibodies made by a man to his own sperm, known as “antisperm antibodies,” are measured by the “immunobead” test (IBT).
White blood cells may be drawn to the semen by infection or inflammation, and damage the sperm. This condition is known as “pyospermia.” Tests for pyospermia count the number of white blood cells in the semen. Typically, less than one million cells per milliliter is normal, but more than three million white blood cells per milliliter may affect a man’s fertility.
A sperm’s basic job is to transport its genetic cargo to the egg. The quality of the DNA contained within the sperm may affect egg fertilization and early embryo development. One commercial test of DNA quality is the “Sperm Chromatin Structure Assay” (SCSA). The SCSA measures DNA melting in acid, called “denaturation.” Studies in the scientific literature disagree over whether DNA denaturation as measured by the SCSA predicts embryo development and pregnancy.
Other tests of DNA quality include the Comet and the terminal uridine deoxynucleotidyl transferase nick end labeling (TUNEL) assays, both commonly performed in molecular biology laboratories for scientific studies of cells. In scientific journals, researchers have reported correlation between Comet and TUNEL results and embryo quality and in-vitro fertilization (IVF) outcomes. Although not yet widely available, Comet and TUNEL may be promising tests to measure sperm DNA quality.
DNA is organized in cells in chromosomes. Two currently available ways of testing chromosomes are the karyotype, in which a picture is made of the 23 pairs of human chromosomes and missing or extra areas are identified, and the Y-chromosomal microdeletion assay, where specific regions of the Y chromosome are determined to be missing.
These tests screen only a fraction of the many genes that contribute to male fertility. While recommended for men with very low sperm counts or no sperm in the ejaculate, a doctor will balance the costs of these tests and the chance of discovering a genetic condition in an individual man.