What is Sperm Morphology?

One of the most controversial areas in the field of reproductive medicine is the potential impact of psychological factors on pregnancy rates. Although there are a variety of old wives’ tales which support the notion that stress hampers reproduction function, this theory has been challenging to confirm. There have been dozens of studies which have investigated the relationship between psychological symptoms prior to and during ART cycles and subsequent pregnancy rates, with conflicting results. Some have shown that the more distressed the women prior to and during treatment, the lower the pregnancy rates, while other studies have not.

Not all of an individual’s sperm look exactly alike. Abnormalities in sperm size and shape can occur in the head, midpiece, or tail.

In some cases, these mutations or changes do not impact the sperm’s overall functionality. In other situations, the sperm may not be able to move properly or quickly enough to reach, puncture, or enter the egg’s membrane.

Doctors usually assess sperm morphology during a general semen analysis or fertility test. On its own, an abnormal or low sperm morphology score is typically not an indication of infertility.

Sperm morphology tests

Sperm morphology tests examine semen samples under a microscope and calculate the percentage of sperm with a normal form (NF) in the total sample.

Requirements for a normally formed sperm include:

  • a smooth rimmed, oval shaped head
  • A head that is between 2.5 to 3.5 micrometers (μm) wide and 5 to 6 μm long
  • An acrosome (a membrane with enzymes capable of penetrating the egg’s membrane) tip that covers between 40 and 70 percent of the sperm head
  • A head free of large vacuoles (fluid filled organelles) and have no more than two small vacuoles that take up less than 20 percent of the total head
  • Midpiece of the sperm (the segment between the head and tail) should be about the same length as the head but much slimmer
  • An uncoiled, 45 μm-long tail that should be thinner than the sperm head and midpiece
  • Free from head or tail defects

Lab technicians usually process sperm morphology tests by putting a small portion of the semen on a glass slide, letting it air dry, and then staining it with a dye that makes individual sperm easier to see under the microscope.

Technicians typically calculate the percentage of NF sperm out of 200 or more sperm in one segment of the sample.

Sperm morphology tests can also be assessed using image analysis technology, such as a computer-aided sperm morphometric assessment (CASA).

According to the World Health Organization, computer based tests are more precise and reliable than manual tests because of the removed risk of human error.

One round of testing is not enough to fully assess semen or sperm quality.

There is a high level of variation between different people, as well as between samples from the same individual. Factors such as human error, contamination, mislabeling, and time before processing also make multiple tests necessary.

It typically takes three or more tests that produce the same or similar results to confirm qualities such as morphology, vitality, and mobility.

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