19 March 2026
A recent scientific study of approximately 15,000 men aged 18-45 years by the University of Manchester (England), Queen’s University (Ontario, Canada), and Cryos International (Aarhus, Denmark) has found that sperm motility (ability to swim forward) increases in summer and declines in winter regardless of seasonal changes in temperature. Researchers found that sperm motility peaks in June and July and reaches its lowest in December and January. (1)
Why study seasonal sperm motility?
Male fertility, along with human physiology, varies for reasons that are not yet fully understood (although hormone, metabolic and sleep patterns, diet and environmental factors are all thought to be factors). Sperm motility is an important measure of quality and its ability to reach and fertilize an egg, with higher motility thought to increase pregnancy outcomes. Previous studies into sperm motility have been small, often focused in one location, with conflicting results. As such, this recent study published on 21 February 2026 is important because it is large-scale, examining sperm of 15,581 men who applied to become sperm donors between 2018 and 2024 in two different countries and climates (Denmark and Florida) to see if sperm motility and quality changes during the year. In Denmark, where 10,670 of the male participants lived across four Danish cities (Aarhus, Aalborg, Odense, and Copenhagen), winters are cold and summers are mild. Whereas in Orlando in Florida, where 4,911 of the participants lived, weather is hot and sunny all year.
Researchers assessed each sample’s sperm concentration, volume, motility and number that were swimming within an hour of each sample being provided using the same computer-assisted semen analysis (CASA) system and standardised temperature-controlled protocols. They also studied data on temperatures at the time the sperm sample was taken and two months prior to this when sperm starts to develop. Their results showed that sperm motility is highest in June and July and reaches its lowest in December and January in both Florida and Denmark. As such, differences in temperature did not account for seasonal changes in sperm motility. They also found that sperm concentration and semen volume remained steady all year, indicating that seasonal changes do not impact sperm production. Moreover, they found that men’s age impacted sperm motility with highest rates amongst men aged 25-35 years old.
What do seasonal changes in sperm motility mean for male fertility?
These recent research findings indicate that seasonal changes in sperm motility are a relevant factor when assessing sperm quality and evaluating the suitability of prospective sperm donors. Understanding these seasonal changes in male fertility could also help clinicians and patients optimise the timing of fertility testing and treatment protocols and improve guidance for those looking to conceive.
Overall, these findings indicate that fertility clinicians should factor in the time of year when assessing sperm samples, with a winter sample differing from one provided in summer. That said, seasonal changes and impact on male fertility cannot be viewed in isolation and information on lifestyle, health and diet should also be taken into account as these are known to affect sperm quality. As such, further research is needed to study sperm quality and motility in different populations and factor in lifestyle data as well. This will help further improve understanding of human physiology and its correlation with male fertility.
Read more about male fertility in our previous blog “Male Infertility And Reproductive Health: A Growing problem?”.
Specialist Fertility and Family Law, Advisory & Consultancy
Giving falling fertility rates across the world, it is important to preserve and maximise individual fertility and adopt proactive approaches to family building, fertility treatment, pregnancy, birth and family life. Bespoke fertility and family law strategies and specialist advisory and consultancy help inform approaches to (in)fertility and reproductive health, as well as effectively plan family building journeys. They also navigate a range of legal and practical issues and risks, placing family building and life on a firm footing including:
- Complex personal and family situations.
- Legal and practical aspects of fertility preservation.
- Family building options and issues due to impaired fertility/infertility, cancer diagnosis or other illness, unsuccessful conception attempts, change in gender, change in personal circumstances, delayed parenthood.
- Posthumous conception with the eggs, sperm and embryos of a deceased loved one (e.g. due to illness or accident).
- Legal and practical aspects of assisted conception with a known donor, anonymous/identity-release donor or co-parent (e.g. legal parentage, parental rights, financial responsibility and dispute mitigation).
- Legal and wider aspects of international surrogacy or a UK surrogacy arrangement.
- Legal parentage issues and disputes (e.g. concerning DNA testing, direct-to-consumer genetic testing, rectification of birth certificate, declaration of parentage, step-parent adoption, recognition of overseas adoption, parental order).
- Care and upbringing of children following a dispute with an ex-partner, parent, donor or surrogate (e.g. contact, residence, financial arrangements, parental responsibility, specific issue or prohibited steps).
- Issues with importing frozen gametes/embryos into the UK for use in fertility treatment and surrogacy (e.g. due to anonymous and commercially obtained gametes/embryos which engage UK public policy restrictions).
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Footnote
(1) Lassen E, Pacey AA, Skytte AB, Montgomerie R. Seasonal trends in sperm quality in Denmark & Florida. Reprod Biol Endocrinol. 2026. doi: 10.1186/s12958-026-01537-w.
