How reliable is sperm morphology as a fertility indicator? 

Sperm morphology refers to the shape and structure of sperm and is one of the key factors assessed in a semen analysis. According to World Health Organization guidelines, a sample is considered normal if at least 4% of sperm have a normal shape. If fewer than 4% are normal, the condition is called teratozoospermia (WHO, 2021). However, these thresholds have changed over time, and this has raised questions about how reliable morphology alone is as a measure of fertility. 

In many cases, morphology results are reported as a single percentage, without identifying the specific types of abnormalities. This makes it difficult to fully understand the underlying causes, which may include genetic, environmental, or medical factors. 

Some genetic conditions are known to cause very specific sperm abnormalities. For example, globozoospermia is a rare condition where sperm have round heads and lack the structure needed to fertilize an oocyte. Another condition, macrozoospermia, involves abnormally large sperm heads and is often linked to genetic mutations. In these cases, specialised fertility treatments such as ICSI may be required (Pelzman et al., 2024). 

Environmental and lifestyle factors can also affect sperm shape. Heat exposure is particularly important, as sperm production requires a temperature slightly lower than body temperature. Frequent use of saunas, tight clothing, or heated environments can negatively affect sperm development (Hoang-Thi et al., 2022). Medical conditions such as varicocele can also increase testicular temperature and impair sperm quality. Treating varicocele has been shown to improve sperm morphology in some men (Fallara et al., 2023). 

Overall, sperm morphology is influenced by a combination of genetic, environmental, and medical factors. While it provides useful information, it should not be considered in isolation. A more complete assessment includes identifying specific abnormalities and considering underlying causes. 

Pelzman DL, Sandlow JI. Sperm morphology: Evaluating its clinical relevance in contemporary fertility practice. Reprod Med Biol. 2024 Jun 24;23(1):e12594. doi: 10.1002/rmb2.12594. PMID: 38915912; PMCID: PMC11194684. 

Fallara G, Capogrosso P, Pozzi E, Belladelli F, Corsini C, Boeri L, Candela L, Schifano N, Dehò F, Castiglione F, Muneer A, Montorsi F, Salonia A. The Effect of Varicocele Treatment on Fertility in Adults: A Systematic Review and Meta-analysis of Published Prospective Trials. Eur Urol Focus. 2023 Jan;9(1):154-161. doi: 10.1016/j.euf.2022.08.014. Epub 2022 Sep 20. PMID: 36151030. 

Hoang-Thi AP, Dang-Thi AT, Phan-Van S, Nguyen-Ba T, Truong-Thi PL, Le-Minh T, Nguyen-Vu QH, Nguyen-Thanh T. The Impact of High Ambient Temperature on Human Sperm Parameters: A Meta-Analysis. Iran J Public Health. 2022 Apr;51(4):710-723. doi: 10.18502/ijph.v51i4.9232. PMID: 35936544; PMCID: PMC9288403. 

World Health Organization. (2021). WHO laboratory manual for the examination and processing of human semen (6th ed.). Geneva: World Health Organization.