Sperm Morphology

Sperm morphology, one of the many attributes found in a semen analysis, looks at the shape and size of sperm. The understanding is that if a sperm is not normal – it doesn’t have the ideal shape, then the sperm will have difficulty swimming all the way up to the fallopian tube to meet the egg. However, fertility experts don’t take this number too seriously.

Background

A given sperm has a limited amount of time to swim up to the fallopian tube to fertilize the egg – typically between 12 to 18 hours. If the egg is not fertilized during that time, the egg is reabsorbed by the body and the couple has to wait until her next fertile window to try again. Many factors contribute to the success of the sperm’s journey, including morphology. It is understood that sperm with a less than ideal shape will not reach the fallopian tube on time. It is with this understanding that several decades ago fertility experts began to create systems to assess sperm morphology.

Introduction

While some doctors have used sperm morphology assessment for several decades to grade male fertility, others have rejected the importance of this measurement. According to a review released in 2017 by Andrology, the disagreement between doctors on the importance of sperm morphology has to do with the lack of technical standardization. The scientific community has been classifying and developing sperm morphology assessments since the early 1950’s. In an effort to try to standardize these assessments, in 1980 the World Health Organization (WHO) began the process of standardizing semen analysis procedures, including sperm morphology evaluation.

The Decline of Morphology

The WHO published the first manual for the Examination and Processing of Human Semen in 1980. The lowest allowable percentage for what is considered normal morphology in 1980 was 80.5%. Seven years later, in 1987, the second edition of the manual was published. This time the percentage for normal morphology had dropped to 50%. By 1999, after incorporating the Kruger criteria – which added a significant advancement in assessing sperm morphology, the WHO dropped the minimum normal sperm morphology to 14%. The 2010 edition of the WHO manual, which we are currently using, defines a normal sperm morphology as 4%. While it is true that over the decades the WHO criteria for normal sperm morphology have become progressively more rigorous, there is sufficient data available indicating that during the past few decades there has been a constant decline in sperm morphology. A study conducted in southern Europe, and published in 2022 by Biology, looked at semen samples analyzed between 1997 and 2017. The study noted that between 1977 and 2017 the average sperm morphology dropped from 20 to 4%. The Mayo Clinic performed a retrospective study which was published in 2011 by the Journal of Fertility and Sterility. The study looked at patients from two different eras: 1996–1997 (era 1) and 2005–2006 (era 2). The conclusion of the study was that sperm morphology was better a decade earlier allowing for better IUI results. The study concluded by saying:

“ There was a strong relationship between morphology and IUI outcome in era 1 that was not present in era 2”.

Assessing Sperm Morphology

Sperm morphology analysis involves preparing a stained semen smear and examining it under a high-power microscope (often ×1000 magnification). Depending on the lab, between 100 to 200 sperm are looked at to calculate the percentage of normally shaped sperm. The lab technician looks at the sperm's head, midpiece, and tail for any abnormalities. For example, the head must be oval-shaped with smooth edges, a specific size (5-6 μm long, 2.5-3.5 μm wide), and an acrosome (enzyme cap) covering 40-70% of the head. The midpiece should be about the same length as the head, but much thinner, and the tail should be uncoiled, about 45 μm long, and thinner than the head and midpiece. A sperm that does not meet this criteria is considered abnormal. As can be expected, since the measurements are done manually, there is a lot of room for human error. Anyone can tell if a sperm has two heads or two tails, but it becomes more subjective to determine if a sperm has an oval-shaped head with smooth edges. It is because of this lack of precision that many fertility experts are ignoring this parameter on a semen analysis.

Abnormally Shaped Sperm Are Not That Bad After All

According to the American Society of Reproductive Medicine (ASRM), an abnormally shaped sperm can not only fertilize an egg, but there is also no correlation between the shape of a sperm and its genetic material that are passed to the offspring. So then why worry about sperm morphology? While it is true that some men with abnormally shaped sperm may have no trouble getting their partners pregnant, having a higher number of abnormally shaped sperm has been associated with decreased fertility. In clinic, when we see a high number of abnormally shaped sperm, it is typically associated with other sperm issues such as low count and/or motility.

Several hypothesis have been proposed to explain the decline in human sperm morphology. The Kamikaze hypothesis proposes that different kinds of sperm might be adapted for different functions. In this case, the abnormally shaped sperm surround the normally shaped sperm, protecting it from possible invaders. Similar to football where the offensive line protects the quarterback. Another hypothesis, one that is very common in the animal kingdom, is Sperm Competition. Here sperm from two or more males compete to fertilize the egg of a single female. In bottlenose dolphins, for example, where as many as eight males compete for the same egg of one female, sperm motility is about 90% and normal sperm morphology is about 95%. The Sperm Competition hypothesis proposes that as humans have evolved to more monogamous relationships, sperm don’t have to fight so hard to make it to the egg. In other words, human sperm morphology appears to be a consequence of their evolutionary history of a lack of sperm competition. Emeritus Professor Gerhard van der Horst, a leading comparative spermatologist, once wrote: "Why produce a Rolls Royce sperm like dolphins (energy expensive) if you can produce poor sperm as in humans that are still capable of fertilizing the oocyte (egg)”.

“ Why produce a Rolls Royce sperm like dolphins (energy expensive) if you can produce poor sperm as in humans that are still capable of fertilizing the oocyte (egg)”.

How To Improve Morphology And Other Sperm Attributes

Until scientists figure out a way to consistently measure sperm morphology, the question will remain of how much importance sperm morphology has on fertility. However, embracing a healthy lifestyle, which can include daily aerobic exercise, a plant-based diet, stress-reducing exercises, and acupuncture, can help not only improve sperm morphology, but also sperm motility and count. And, unlike sperm morphology, there is no doubt that low motility and low count will negatively affect fertility.

Acupuncture And Sperm Morphology

Recent research has shown time after time the benefits of acupuncture on male fertility. A review published on December of 2024 by the journal of Integrative Medicine in Nephrology and Andrology, gives an overview of TCM’s perspective on male infertility, explores the clinical efficacy of acupuncture in treating male infertility and the corresponding mechanisms. The review mentions several clinical studies indicating that acupuncture improves sperm concentration, viability, and morphology, while also enhancing blood viscosity and reducing varicocele (an enlargement of the veins in the scrotum) diameter.

Conclusion

While there is no agreement on how to assess sperm morphology, or even a clear understanding to say that the decline in sperm morphology in the past 40 years is due to a real decline in sperm morphology or that the standards to measure this parameter are now more strict, there is no doubt that a high number of abnormally shaped sperm can have a negative impact on fertility. Maintaining a healthy exercise routine, a lifestyle conducive to low stress, and a diet free from inflammatory foods such as animal protein, can not only improve male fertility, but improve overall health.