General information about semen characteristics

By Sofia Spanou –Embryologist, Sperm-bank Director

Quantifiable attributes of semen

Semen has two major quantifiable attributes, the total number of spermatozoa that reflects sperm production by the testes and the patency of the post-testicular duct system; and the total fluid volume contributed by the various accessory glands that reflects the secretory activity of the glands.

Days of abstinence

The days of abstinence for a semen sample to be collected is optimum between a minimum of 2 days and a maximum of 7 days.

pH of semen

WHO retains the consensus value of 7.2 as a lower threshold value for the semen from fertile men. If the pH is less than 7.0 in a semen sample with low volume and low sperm numbers, there may be ejaculatory duct obstruction or congenital bilateral absence of the vas deferens, a condition in which seminal vesicles are also poorly developed.

Categories of sperm movement

According to WHO 5th edition, the motility of each spermatozoon is graded as follows:

  • Progressive motility (PR): spermatozoa moving actively, either linearly or in a large circle, regardless of speed.
  • Non-progressive motility (NP): all other patterns of motility with an absence of progression, e.g. swimming in small circles, the flagellar force hardly displacing the head, or when only a flagellar beat can be observed.
  • Immotility (IM): no movement.

With the lower reference limit for total motility (PR + NP) is 40% and for progressive motility (PR) is 32%.

Lower reference limit for sperm concentration

According to WHO 5th edition, the lower reference limit for sperm concentration is 15 × 106 spermatozoa per ml.

Lower reference limit for total sperm number

According to WHO 5th edition, the lower reference limit for total sperm number is 39 × 106 spermatozoa per ejaculate.

Normal forms of spermatozoa

Human semen samples contain spermatozoa with different kinds of malformations. Abnormal spermatozoa generally have a lower fertilizing potential, depending on the types of anomalies, and may also have abnormal DNA. Morphological defects have been associated with increased DNA fragmentation, an increased incidence of structural chromosomal aberrations, immature chromatin and aneuploidy. The lower reference limit for normal forms is 4%.

Reference values

At least 50% of couples referred for infertility investigation and treatment are found to have a contributing male factor the lower reference limits 15 × 10 6 /mL for concentration, 32% for good forward progressive movement within 60 minutes of ejaculation and 4% for normal morphology (WHO manual, 5th edition, 2010).