Sperm navigating a maze, symbolizing fertility challenges.

Sperm Morphology: Does Shape Really Matter for Fertility?

Jordan Keane in Health & Wellness August 2025 • 4 min read.

"Unpacking the latest research on sperm shape and its impact on assisted reproductive technologies (ART)."

Sperm shape has long been linked to a man's fertility. The 'strict morphology criteria' (SMC), developed by Menkveld and Kruger, has been a standard for evaluating sperm forms, based on the spermatic forms recovered from the os of female cervices. The World Health Organization (WHO) recommends using SMC, setting 4% normal forms as the lower limit. But is morphology as crucial as we once thought?

When couples face infertility, sperm morphology is often one of the first things assessed. However, the importance and clinical application of morphology results are now being questioned. This article examines the current research on sperm morphology and its value in guiding decisions about assisted reproductive technology (ART).

Once considered a strong predictor of pregnancy rates, especially in procedures like intrauterine insemination (IUI) or in vitro fertilization (IVF), recent studies challenge this view. This article clarifies the evolving role of sperm morphology and helps couples understand how it factors into their fertility journey.

The Shifting Significance of Sperm Morphology

Sperm navigating a maze, symbolizing fertility challenges.

It's true that men in infertile relationships often have a lower percentage of sperm with normal shapes compared to fertile men. While testicular issues can lead to more abnormal sperm, the absence of normal-shaped sperm doesn't necessarily prevent pregnancy through natural means, IUI, or IVF. This challenges the long-held belief that <4% normal sperm automatically necessitates IVF.

A recent meta-analysis revealed that pregnancy rates via IUI didn't significantly differ whether men had >4%, <4%, or even <1% normal sperm morphology. Hotaling et al. found similar results for IVF and IVF with intracytoplasmic sperm injection (ICSI). The current consensus suggests that abnormal sperm morphology alone isn't a major obstacle to pregnancy across various ART methods.

Intra- and interlaboratory variation: The evaluation of sperm morphology can vary widely between labs, even when using the same standards.
SMC Stringency: Over time, the criteria for 'normal' sperm have become stricter, impacting average counts.
Sample Size: Morphology assessments are based on only 200 sperm, a small fraction of daily sperm production.

These limitations raise questions about the reliability of sperm morphology as a standalone predictor. A survey by Gatimel et al. revealed that only 23% of physicians found sperm morphology assessment to be very relevant, while 53% considered it fairly relevant and 24% sparsely relevant. Significant differences exist even among reproductive endocrinologists, embryologists, and urologists, further complicating the clinical picture.

Rethinking the Role of Morphology in Fertility Decisions

While specific, rare morphological issues (like globozoospermia) require IVF with ICSI, routine morphology assessments may not be as critical as once believed. Instead of focusing solely on sperm shape percentages, doctors should consider a broader range of factors when guiding couples through ART options.

Quantitative assessments of abnormal sperm shape are inconsistent. As a result, abnormal sperm morphology does not reliably predict lower pregnancy rates for IUI or IVF. Further research is needed to develop a more objective and standardized sperm morphology assessment to return the clinical significance of morphology criteria.

All men in an infertile relationship should be evaluated by a male infertility specialist. Many male factors can be improved to yield better chances of achieving a pregnancy. A quantitative percentage threshold for normal sperm is not sufficiently reliable for routine use in the reproductive clinical setting and certainly should not be used in selecting the ART route for the treatment of infertile couples.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.euf.2018.07.029, Alternate LINK

Title: Role Of Sperm Morphology In Deciding Between Various Assisted Reproduction Technologies

Subject: Urology

Journal: European Urology Focus

Publisher: Elsevier BV

Authors: Taylor P. Kohn, Jaden R. Kohn, Dolores J. Lamb

Published: 2018-05-01

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Everything You Need To Know

1

What is sperm morphology and why is it important?

Sperm morphology refers to the shape of sperm cells. It's a critical aspect of fertility assessment because sperm shape has been linked to a man's fertility. The 'strict morphology criteria' (SMC), developed by Menkveld and Kruger, is a standard for evaluating sperm forms, where the World Health Organization (WHO) recommends using SMC and setting 4% normal forms as the lower limit. The implications involve the ability to penetrate and fertilize an egg, with abnormal shapes potentially hindering this process. Different ART methods such as intrauterine insemination (IUI) or in vitro fertilization (IVF) are being explored as a result.

2

How has the understanding of sperm morphology's impact on pregnancy changed?

Sperm morphology was once considered a strong predictor of pregnancy rates, especially in procedures like intrauterine insemination (IUI) or in vitro fertilization (IVF). However, recent studies challenge this view. It was believed that if a man had less than 4% normal sperm morphology, it would automatically necessitate IVF. Recent studies showed that pregnancy rates via IUI didn't significantly differ whether men had >4%, <4%, or even <1% normal sperm morphology. For IVF and IVF with intracytoplasmic sperm injection (ICSI) the results were similar, suggesting that abnormal sperm morphology alone isn't a major obstacle to pregnancy across various ART methods.

3

What are the main limitations when evaluating sperm morphology?

Several limitations affect the reliability of sperm morphology assessments. Intra- and interlaboratory variation means that the evaluation of sperm morphology can vary widely between labs, even when using the same standards. The SMC stringency also impacts average counts because the criteria for 'normal' sperm have become stricter over time. Finally, morphology assessments are based on a small sample size of only 200 sperm, a small fraction of daily sperm production. These factors raise questions about sperm morphology as a standalone predictor.

4

How is the role of sperm morphology changing in fertility decisions?

The significance of sperm morphology in fertility decisions is shifting. While specific, rare morphological issues like globozoospermia may require IVF with ICSI, routine morphology assessments may not be as critical as once believed. Doctors are now advised to consider a broader range of factors when guiding couples through ART options, rather than focusing solely on sperm shape percentages. A survey revealed that only 23% of physicians found sperm morphology assessment to be very relevant.

5

How does sperm morphology relate to Assisted Reproductive Technologies (ART)?

Assisted Reproductive Technologies (ART) are medical procedures used to help couples conceive. Examples of ART methods include intrauterine insemination (IUI), in vitro fertilization (IVF), and IVF with intracytoplasmic sperm injection (ICSI). Sperm morphology is relevant to ART because it helps assess the quality of sperm, which affects the success rates of these procedures. When sperm morphology is abnormal, it may impact the choice of ART method, such as considering IVF with ICSI, where a single sperm is injected directly into an egg.