There are several ways to judge the quality of a spermatozoon. When analyzing morphology, the main question is to know what a “normal” spermatozoa is and which link may exist with fertility. Fertile men, i.e. who were able to induce a viable pregnancy and give rise to a child, have a percentage of normal spermatozoa that is not considerably different from that found for unfertile men.

Laboratories performing sperm tests may use either the WHO Laboratory Handbook (1999, 2010), the strict criteria (Kruger TF et al. Fertil.Steril. 46, 1118 (1986)) or other classifications as reference guides. The WHO 2010 edition aggregates the most advanced knowledge on the subject, the reason why we will follow here its recommendations.

Definition of a normal spermatozoon according to WHO (2010)

For a spermatozoon to be considered normal, both its head and tail must be normal. All borderline forms should be considered abnormal. The head should be smooth, regularly contoured and generally oval in shape. There should be a well-defined acrosomal region comprising 40–70% of the head area (Menkveld et al. 2001). The acrosomal region should contain no large vacuoles, and not more than two small vacuoles, which should not occupy more than 20% of the sperm head. The post-acrosomal region should not contain any vacuoles. The midpiece should be slender, regular and about the same length as the sperm head. The major axis of the midpiece should be aligned with the major axis of the sperm head. Residual cytoplasm is considered an anomaly only when in excess, i.e. when it exceeds one third of the sperm head size (Mortimer and Menkveld 2001). The principal piece should have a uniform calibre along its length, be thinner than the midpiece, and be approximately 45 µm long (about 10 times the head length). It may be looped back on itself, provided there is no sharp angle indicative of a flagellar break.

Head sizes

The ideal head is oval and smooth. The morphometric measurements (length, width, ellipticity, …) depend on the stain used (Papanicolaou, Diff-Quick). Here are examples of dimensions published by various authors after Papanicolaou staining.
Head sizes Katz (1986) Soler (2003) WHO (2010)
Length (µm)  3.50 – 4.00  4.28 ± 0.50  4.12 ± 0.70
Width (µm)  2.50 – 5.00  2.69 ± 0.31  2.68 ± 0.41


  1. Katz, D.F., Overstreet, J.W., Samuels, S.J., Niswander, P.W., Bloom, T.D., Lewis, E.L. (1986) Morphometric analysis of spermatozoa in the assessment of human male fertility. Journal of Andrology, 7, 203-212. Kruger, T.F., Franken, D.F. Atlas of Human Sperm Morphology Evaluation. Francis & Talor. A Parthenon Book, ISBN 1842142771
  2. Kruger, T.F., Franken, D.F. Atlas of Human Sperm Morphology Evaluation. Francis & Talor. A Parthenon Book, ISBN 1842142771
  3. Soler, C., De Montserrat, J.J., Gutiérrez, R., Nunez, J., Nunez, M., Sancho, M., Pérez-Sanchez, F., Cooper, T.G. (2003) Use of the Sperm-Class Analyser for objective assessment of human sperm morphology. International Journal of Andrology, 26, 262-270
  4. Faber (2007)
  5. Kruger TF, Menkveld R, Stander FS, Lombard CJ, Van der Merwe JP, van Zyl JA, Smith K. 1986. Sperm morphologic features as a prognostic factor in in vitro fertilization. Fertil Steril 46: 1118-1123.
  6. Menkveld R, Wong WY, Lombard CJ, Wetzels AM, Thomas CM, Merkus HM, Steegers-Theunissen RP. 2001. Semen parameters, including WHO and strict criteria morphology, in a fertile and subfertile population: an effort towards standardization of in-vivo thresholds. Human reproduction 16: 1165-1171.
  7. Mortimer D, Menkveld R. 2001. Sperm morphology assessment–historical perspectives and current opinions. Journal of andrology 22: 192-205.
  8. WHO. 1999, 2010. WHO Laboratory Manual for the Examination of Human Semen and Sperm-Cervical Mucus Interaction. Cambridge: Cambridge University Press.