Morphology refers to the shape, size, and structure of sperm. Sperm morphology typically takes into consideration the head and tail of the sperm, as these can have a direct impact on the sperm's ability to reach and fertilize the egg. Abnormal sperm morphology can have an adverse effect on fertility and can be diagnosed in a semen analysis. 

What is sperm morphology?

Sperm morphology refers to the size, shape, and structure of sperm. Analyzing sperm morphology involves looking at sperm under a microscope to check the shape, size, alignment, and texture of the head, acrosome (a cap-like structure covering the sperm head), midpiece or “neck,” and tail. Sperm morphology has been used to evaluate male fertility since the early 1900s, and remains a central part of semen analysis.

While humans have greatly varied sperm shapes — both across and within different individuals — having some amount of morphologically “normal” sperm is important for fertility. Normal morphology values depend on the type of testing performed. Using Kruger’s strict criteria, which regards even minute alterations of sperm as “abnormal,” 4% or more normal sperm is considered normal. Using the less strict WHO protocols, morphology results of at least 14% is normal.

Morphology and male fertility 

Research indicates that infertile people tend to have lower normal morphology and higher numbers of sperm defects compared to fertile people, along with reduced sperm count and motility and increased sperm DNA fragmentation.

However, in a study from 2017, even men with 0% normal forms of sperm still conceived without assisted reproduction in 30% of cases. This suggests that, while morphology may impact fertility, it should not be used on its own to predict the potential for pregnancy. While sperm morphology remains an important component in semen analysis, more research is needed to clarify its impact on fertility.

Improving sperm morphology

Studies suggest that lifestyle changes may improve your sperm morphology, which may in turn benefit your fertility. These changes may include:

  • stopping smoking
  • limiting alcohol consumption and avoiding recreational drugs (in particular, cocaine use has been associated with increased numbers of abnormal sperm)
  • maintaining a healthy weight, though evidence is mixed
  • reducing stress
  • following a healthy diet, such as the Mediterranean diet, or taking antioxidant supplements

Normal sperm morphology may also worsen with age. If possible, conceiving or freezing sperm at a younger age may yield better sperm parameters, including morphology.

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