Kruger's strict criteria
The Kruger method (or strict morphology) is the most precise and widely accepted standard for assessing morphological defects in spermatozoa. The Kruger criteria evaluate only those sperm that are completely normal in each anatomical part.
What is sperm morphology?
The morphology of sperm describes their shape and structure — head, neck and tail. Deviations in these structures can affect the ability of the sperm to reach and fertilize the egg. Accurate assessment of morphology is a critically important part of sperm analysis, especially in couples with reproductive difficulties.
What are Kruger's strict criteria?
The Kruger method (or strict morphology) is the most precise and widely accepted standard for assessing morphological defects in spermatozoa. Unlike more general methods, the Kruger criteria evaluate only those sperm that are completely normal in each anatomical part. All even minimal deviations are considered “abnormal”. This makes the method more sensitive, but also more informative.
Why is this important?
Spermatozoa that meet all these requirements are the ones that most successfully:
- They reach the ovum;
- Penetrate through its shell (zona pellucida);
- They contribute to the development of a healthy embryo.
Why is the norm of 14% better than that of 4%?
According to older requirements, normal morphology ≥ 14% is considered an indicator of good fertility. In 2010 The WHO has reduced the reference limit to 4%, which often leads to an underestimation of subclinical problems. Many males with a morphology of 5— 6% have difficulty fertilization or a poor prognosis in insemination.
Advantages of the threshold of 14%:
- Allows earlier detection of male factor;
- Better correlation with success in natural conception and insemination;
- More accurate planning of in vitro strategy (for example, need for ICSI).
What does low Kruger morphology mean?
A low percentage of normal forms (less than 4— 5%) usually indicates:
- Disrupted process of spermatogenesis;
- Possible genetic or epigenetic abnormalities;
- Decreased ability to enter the ovum;
- Increased risk of fertilization with defective sperm.
Our approach in the clinic
In our laboratory, we use the strict Kruger criteria and a threshold of 14% not because it is stricter, but because it is more informative. Our goal is not just to measure fertility, but to understand and improve it. This helps us to make more precise decisions and offer the most appropriate treatment method for each couple.
Don't worry about numbers — we'll guide you through them. The important thing is not how “perfect” your sperm are, but how we can get the best out of them together.