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Spermatozoa

There are several ways to judge the quality of a spermatozoon. When analyzing morphology, the main question is to know what a “normal” spermatozoon 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 infertile 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 caliber 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

Parameters of the EQC test

The EQC test will present you several possible answers for the head, midpiece, and tail. You can make only one choice. Although you may not be used to grade head shapes in your day-to-day activity, grading head shape is a convenient way of communicating sperm characteristics both to colleagues and medical staff. In our view, it is an important parameter to monitor in an External Quality Control scheme.

Sperm head: size and shape

Several head shapes and sizes have been described by the WHO (1999, 2010).

Parameters Morphological aspects
Normal regular oval shape
Macrocephalic the head is clearly above the normal
Microcephalic the head is present but clearly smaller than the normal size
Elongated the head has the form of a cigar
Pyriform the head has the form of a pear
Amorphous the head has slight to strong deviation from oval form
Double two heads attached to one or two midpieces and tails
Pin the head is absent, but the cells are alive and usually move
Round the head is perfectly spheric and no acrosome is present

 

 

 

 

 

 

 

 

Presence of vacuoles

The presence 1-2 vacuoles in the sperm head can be considered as normal. More than 2, should be considered as abnormal, according to the strict criteria.

Acrosome size

The acrosomal region should be well defined and be comprising 40-70% of the head area.

Midpiece

The midpiece should be slender (<1 µm thick) and about 1.5 times the head length. The cytoplasmic droplet should be less than half the width of the head.

Parameters Morphological aspect
Angulated angulation of the midpiece with respect to the head axis
Asymetrical asymetrical insertion of the midpiece into the head
Thick or irregular midpiece
Thin abnormally thin midpiece (absence of mitochondrial sheath)
Cytoplasmic droplet cytoplasmic remnant larger than half of the head’s width

Tail

The tail should be straight, uniform, thinner than the midpiece, uncoiled and about 45 µm long. Tail defects are presented below.

Parameters Morphological aspect
Short or incompletely formed tail Normal tail length is about 40-50 µm.
Multiple A single head may be associated with multiple tails
Irregular width This parameter may be associated with osmotic effects or staining artifacts
Bent Depending on the smear flagella may be curved, indicating movement of the sperm during the fixation procedure, or remain straight
Coiled Various forms of coiling may occur, either during sperm maturation or after sperm collection (osmotic effects)

 

Bibliography

  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 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.