A semen analysis is used to determine whether a man might be infertile—unable to get a woman pregnant. The semen analysis consists of a series of tests that evaluate the quality and quantity of the sperm and the environment they reside in, the semen.
The semen analysis also can be used to count sperm after a man has had a vasectomy, a procedure that prevents sperm from being released within the ejaculate and that is considered a permanent method of birth control (99.9%) when performed by an experienced surgeon. If sperm are present in the semen, whether still active or not, the man and his partner will have to take precautions to avoid pregnancy. He will have to return for one or more sperm counts until sperm are no longer present in his sample(s).
A semen analysis is performed when a health practitioner thinks that a man or couple might have a fertility problem. Male factors are implicated in up to 50% of infertility cases. Male infertility can have many causes, some that can be treated successfully. If male factors are involved, analysis of the semen is necessary to determine what is inhibiting fertility and, when indicated, to evaluate the feasibility of using assisted reproductive technology (ART) to facilitate pregnancy.
A semen analysis to determine fertility should be performed on a minimum of two samples at least seven days apart over a period of two to three months. Sperm count and semen consistency can vary from day to day, and some conditions can temporarily affect sperm motility and numbers.
When a semen analysis shows abnormal findings, the test is repeated at intervals as determined by the health practitioner.
A semen analysis is also typically ordered following a vasectomy to confirm success of the procedure and repeated as necessary until sperm are no longer present in the semen sample.
The typical volume of semen collected is between 1.5 and 5.5 milliliters (mL) of fluid per ejaculation. Decreased volume of semen would indicate fewer sperm, which diminishes opportunities for successful fertilization and subsequent pregnancy. Excessive seminal fluid may dilute the concentration of sperm.
The semen should initially be thick and then liquefy within 15 to 30 minutes. If this does not occur, then it may impede sperm movement.
Sperm concentration (also called sperm count or sperm density) is measured in millions of sperm per milliliter of semen. Normal is at least 20 million or more sperm per mL, with a total ejaculate volume of 80 million or more. Fewer sperm and/or a lower sperm concentration may impair fertility. Following a vasectomy, the goal is to have no sperm detected in the semen sample.
Motility is the percentage of moving sperm in a sample and graded based on speed and direction travelled. At least 50% should be motile one hour after ejaculation, moving forward in a straight line with good speed. The progression of the sperm, best measured using an automated system, is rated on a basis from zero (no motion) to 4, with 3-4 representing good motility. If less than half of the sperm are motile, a stain is used to identify the percentage of dead sperm. This is called a sperm viability test.
Morphology analysis is the study of the size, shape, and appearance of the sperm cells. The analysis evaluates the structure of the sperm, whereby greater than 50% of those cells examined must be normal in size, shape, and length. The more abnormal sperm that are present, the lower the likelihood of fertility. Abnormal forms may include defective heads, midsections, tails, and immature forms. More than 14% should have normal heads. To see an image of a normal sperm, see the MedlinePlus Medical Encyclopedia page on sperm.
Semen pH should be between 7.2 and 7.8, fructose at 150-600 mg/dL, and there should be fewer than 2000 white blood cells per mL. A pH of 8.0 or higher may indicate an infection, while a pH less than 7.0 suggests contamination with urine or an obstruction in the ejaculatory ducts.
Agglutination of sperm occurs when sperm stick together in a specific and consistent manner (head to head, tail to tail, etc.) suggesting an immunologic cause to infertility. Clumping of sperm in a nonspecific manner may be due to bacterial infection or tissue contamination.
In an evaluation of a man's fertility, each aspect of the semen analysis is considered, as well as the findings as a whole. Each part of the semen analysis either contributes to confirming male fertility or, if abnormal, lessens it. While abnormal results decrease the chances of fertilization, some couples with poor results may still conceive, with or without assistance, and those with apparently good results may experience difficulties.
Several factors can affect the sperm count or other semen analysis values, including use of alcohol, tobacco, caffeine, many recreational and prescription drugs (e.g., cimetidine), and some herbal medicines such as St. John's wort.
This article was last reviewed on September 30, 2013. | This article was last modified on February 24, 2015.
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