An analysis of 90,125 men with infertility in China found that the proportion meeting a sperm morphology reference threshold fell from 88.9% before the pandemic to 55.1% in 2024. Median testosterone was about 6% lower. Some sperm count and movement measures improved, and the study could not establish that COVID-19 infection caused these changes.
What happened to men's sperm across the pandemic years? An eight-year analysis of semen tests found a mixed pattern. Some measures of number and movement improved, while fewer men met a reference threshold for normal sperm shape and testosterone levels were lower.
Researchers reporting in Basic and Clinical Andrology reviewed records from 90,125 men assessed for infertility at a reproductive medicine center in Chongqing, China, between 2017 and 2024. They compared the period before COVID-19, the pandemic period and the years following the relaxation of public-health restrictions.
Fewer men met the morphology reference threshold
Sperm shape was one of the most striking findings. A sperm has a head, midpiece and tail. Heads can be unusually large or small, and tails may be bent or duplicated. Shape is one aspect considered when assessing sperm and their ability to reach and fertilize an egg.
The World Health Organization uses a reference threshold of 4% normally shaped sperm in semen assessment. In practical terms, this asks whether at least four of every 100 sperm examined have normal morphology.
Before the pandemic, in 2017–2019, 88.9% of the men met that threshold. The proportion fell to 72.7% during the pandemic and to 55.1% in 2024. Conversely, the proportion below the threshold rose from 11.1% to 44.9%, approximately four times the pre-pandemic figure.
These percentages describe the proportion of men meeting the 4% threshold. They do not mean that the percentage of normally shaped sperm in a sample fell from 88.9% to 55.1%.
Median testosterone was about 6% lower
Testosterone also changed over the study period. The hormone contributes to sexual function, muscle mass and reproductive function, including sperm production.
Median testosterone fell from 4.46 ng/mL before the pandemic to 4.19 ng/mL in 2024, a decrease of about 6.1%.
That does not mean the number of men with testosterone deficiency increased by the same percentage. The median concentrations reported remained above commonly used thresholds for assessing deficiency. The investigators drew attention to the downward trend over several years.
Some count and motility measures improved
The changes did not all point in the same direction. Despite the decline in morphology measures, sperm concentration and total sperm count increased during some periods. Progressive motility, the ability of sperm to swim forward, also improved in some comparisons.
Age mattered. Men aged 40 or younger showed recovery or improvement in some semen measures, while improvements were smaller among men older than 40.
A high sperm count alone does not establish good reproductive capacity. A sample may contain many sperm but have less favorable morphology or movement. Equally, a lower proportion of normally shaped sperm can coexist with favorable results on other measures.
Equipment and methods used to measure sperm count and motility changed during the study period. The measured improvements therefore cannot all be interpreted as improvements in biological fertility.
Did COVID-19 infection cause the changes?
The study cannot establish that the virus damaged sperm. It compared records from men attending an infertility center at different times. It did not directly compare men known to have been infected with men known to have remained uninfected.
The pandemic also changed living conditions, with potential effects from less exercise, weight gain, stress and insufficient sleep. Such factors could have contributed to changes in semen measures or reproductive hormones.
The participants were men assessed for infertility at a single center in China. The findings cannot simply be generalized to all men.
The results nevertheless illustrate why sperm count, morphology, motility, hormones and age need to be considered together. A low proportion of normally shaped sperm does not by itself establish that pregnancy is impossible. Semen measures can vary with health and the timing of a test.
Further research is needed to explain the changes observed across the pandemic years. Men preparing for pregnancy can discuss a comprehensive assessment with a fertility specialist rather than judging their reproductive capacity from a single semen test.
Source: “Divergent long-term trends in semen quality and reproductive hormones across the COVID-19 pandemic era in infertile men.” Basic and Clinical Andrology, reported November 5, 2026. DOI: 10.1186/s12610-026-00309-1. The original article's illustration was created with generative AI (ChatGPT, OpenAI).
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