What Is Kruger Morphology? Does Sperm Shape Affect the Chances of Pregnancy?

A semen analysis (sperm test) is one of the first evaluations performed for couples embarking on the journey to have a child. This test provides a clear picture of a man’s reproductive potential by examining critical parameters such as sperm count, motility, and morphology. The Kruger Criteria (Strict Criteria) are widely recognized as one of the most reliable and precise methods for evaluating sperm quality. At Umay IVF Center, we evaluate sperm morphology using these rigorous criteria to increase the success of IVF treatment and create the right, personalized treatment plan. So, what exactly do the Kruger criteria mean, and how do they affect the chances of pregnancy? In evaluating male factors during IVF treatment, the shape and structure—or morphology—of sperm cells are just as important as sperm count and motility. As we explained in our blog post titled “Spermiogram,” a Kruger analysis is also performed after a sample is collected. One of the methods used to evaluate sperm morphology is known as the Kruger Strict Criteria. So, what is Kruger morphology? What should the Kruger value be? If the Kruger value is below 4%, is it impossible to have children? Does sperm shape affect IVF success?

What is Kruger morphology?

Kruger morphology is a sperm morphology method based on the evaluation of sperm cells’ shape and structural characteristics using very strict criteria. The sperm cell consists primarily of:

• head,
• midpiece,
• tail

are examined. It is important for these structures to possess the appropriate characteristics so that the sperm can reach the egg, move, and participate in the fertilization process. In the Kruger approach, sperm cells are evaluated according to stricter morphological criteria. For this reason, the percentage of normally shaped sperm may be lower compared to a standard evaluation. Patients sometimes interpret this as “very poor sperm quality.” However, the result should be considered in conjunction with the evaluation criteria used and other sperm parameters.

What is the Kruger sperm test?

In fact, the “Kruger test” is not a separate blood test or a different laboratory test. Kruger is one of the methods used to evaluate sperm morphology in semen analysis. In other words, during a semen analysis, the shape of sperm cells can be evaluated using strict morphological criteria such as the Kruger Strict Criteria. For this reason, the patient’s report may include a result such as: Sperm morphology: 4% . This result indicates that approximately 4% of the sperm cells examined were assessed as having normal morphological characteristics according to the criteria used.

What should the Kruger morphology score be?

When using the Kruger Strict Criteria, around 4% is one of the commonly used lower reference values for normal morphology. However, there is an important detail here: 4% is not a definitive threshold indicating whether pregnancy is possible or not. For example, it is not correct to say that a man with a morphology result of 3% cannot conceive naturally. Similarly, it is not possible to say that a man with a morphology of 5% or 6% necessarily has a higher chance of pregnancy. Sperm morphology should be evaluated in conjunction with sperm concentration, total sperm count, motility, and other characteristics of the couple.

What happens if the Kruger score is below 4%?

This is one of the questions patients ask most frequently. A Kruger morphology below 4% does not, by itself, indicate infertility. For example;

• If the Kruger score is 3%,
• sperm concentration is normal,
• motility is good,

, it may still be possible to achieve pregnancy naturally. Similarly, pregnancy may not occur even in a man whose Kruger morphology is within normal limits. This is because conception does not depend solely on sperm shape. The woman’s age and ovarian reserve, ovulation, the condition of the fallopian tubes, the endometrium, sperm count and motility, embryo development, and other factors specific to the couple must all be evaluated together.

How Does Abnormal Sperm Morphology (Teratozoospermia) Prevent Pregnancy?

The primary function of a normal sperm is to travel through the vagina and uterus to reach the egg and successfully transfer its DNA by penetrating the egg’s outer membrane (fertilization). Abnormalities in sperm morphology can lead to the following problems:

• Inability to Move Forward: Sperm with defects in the tail or neck cannot swim fast enough or in a straight line.
• Failure to Fertilize: Abnormalities in the head structure can prevent the sperm from dissolving the egg’s outer membrane and entering it.
• DNA Damage: Sperm with structural abnormalities may sometimes have a higher risk of DNA integrity being compromised.

Does Kruger morphology affect IVF success?

The relationship between sperm morphology and the success of assisted reproductive technologies has been studied for many years. Poor sperm morphology may be an indicator of male factor infertility in some patients. However, poor sperm morphology alone does not mean that IVF treatment will fail. In particular, with ICSI (intracytoplasmic sperm injection), the embryologist evaluates sperm cells under a microscope, selects a suitable sperm cell, and injects it directly into the egg. For this reason, fertilization and pregnancy can be achieved with ICSI even in patients with severely low morphology. However, it is also incorrect to say that ICSI is mandatory for every patient solely because of low morphology. The treatment method should be determined by evaluating all of the couple’s clinical characteristics. Additionally, in necessary cases, supplementary preparation techniques and microfluidic chip systems aimed at improving sperm DNA quality can also be used.

If the Kruger score is 1% or 2%, is IVF necessary?

The decision to undergo IVF is not based solely on the Kruger result. The Kruger morphology may be as low as 1% or 2% (teratozoospermia). In this case, sperm count, motility, total motile sperm count, history of previous pregnancies, and female factors are evaluated together. While natural conception may be possible for some couples, artificial insemination or IVF may be more appropriate options for others. In particular, when there is a severe male factor, ICSI may be considered as part of the treatment.

Does Kruger morphology change over time?

Yes. Sperm production is a dynamic, ongoing process. For this reason, semen parameters may change over time. Feverish illnesses, infections, smoking, excessive alcohol consumption, obesity, certain medications, severe stress, and environmental factors can affect sperm parameters. For this reason, it is not always accurate to make a definitive assessment based on a single semen analysis result. Especially when an unexpectedly low morphology result is obtained, repeating the semen analysis may be considered depending on the clinical situation.

Are Kruger morphology and sperm DNA damage the same thing?

No. These two concepts are often confused with one another. Kruger morphology evaluates the shape and structure of sperm. Sperm DNA fragmentation tests, on the other hand, aim to provide information about DNA integrity and DNA damage within the sperm cell. Therefore, good morphology does not necessarily mean that the sperm DNA is completely normal. Similarly, poor morphology does not necessarily mean that there is high DNA fragmentation. These tests evaluate different biological characteristics. A sperm DNA fragmentation test is not routinely necessary for every infertile man. Depending on the clinical history—particularly in cases of recurrent pregnancy loss or certain failed assisted reproductive treatments—a physician may consider ordering this test.

How should Kruger morphology be evaluated?

The most accurate approach is not to evaluate the morphology result in isolation. For example, in a semen analysis:

• Sperm concentration: 20 million/mL
• Total motility: 45%
• Progressive motility: 32%
• Kruger morphology: 3%

these results may be found. Simply stating “Kruger 3%, low” is not sufficient to explain the patient’s true reproductive potential. The total number of motile sperm, ejaculate volume, sperm concentration, motility, and the couple’s other clinical characteristics must be evaluated together.

Our Approach at UMAY IVF Center

At UMAY IVF Center, we do not evaluate male infertility based on a single sperm parameter. Sperm count, motility, and morphology must be considered as a whole. Even in cases of low Kruger morphology, we first seek to understand the extent to which this may affect the couple’s overall chances of pregnancy. If necessary, we may plan to repeat the semen analysis, investigate the causes of male factor infertility, or evaluate assisted reproductive techniques. What matters to us is not simply labeling a laboratory result as “normal” or “abnormal,” but accurately explaining what that result means for you. Because in IVF treatment, a single sperm parameter does not, on its own, determine success. UMAY IVF Center A scientific approach. Personalized evaluation. The right treatment at the right time.