O-297 Seasonal trends in sperm quality across Denmark and Florida: a study of 15,125 semen samples
Bibliographic record
Abstract
Abstract Study question Does seasonal variation affect the quality of ejaculates produced by candidate sperm donors in Denmark and Florida (US), and what factors contribute to these trends? Summary answer Sperm quality (grade A concentration) peaks in early summer, drops in winter, influenced by lifestyle and temperature, with unexplained factors remaining significant. What is known already Denmark has a temperate climate with four distinct seasons marked by warm summers and cool winters, whereas Florida (US), experiences a subtropical climate with hot, humid summers and mild winters. Spermatogenesis is temperature-sensitive, and heat exposure is known to affect both the concentration and motility of spermatozoa. Seasonal variation in semen has been studied previously with different methodological approaches and study designs. Existing studies have generally found the lowest sperm concentration and motility during summer (May-August) and the highest during winter (October-January). We suggest that some apparent trends in sperm concentration and motility may result from methodological anomalies introducing bias. Study design, size, duration Data on semen quality from 15,125 candidate sperm donors at the Cryos International sperm banks in the four largest cities of Denmark (Aarhus, Aalborg, Copenhagen, and Odense; 10,637 men) and in Orlando, Florida, USA (4,488 men) from 2018 to 2024 were collected from the sperm bank database and anonymized before analysis. All males were between 18 and 46 years old and lived in or near these cities. Participants/materials, setting, methods Ejaculates were analysed (at22oC) within one hour of production using the same protocols and CASA system in all years at each site. Semen parameters included ejaculate volume, total sperm concentration (106/mL), and the concentration of grade a and b spermatozoa. Semen parameters were analyzed with respect to year and month of production, the city where the ejaculate was produced, and monthly outdoor temperatures. We used longitudinal data from accepted donors to test for methodological biases. Main results and the role of chance While neither ejaculate volume nor total sperm concentration varied significantly across the months of the year in any city, the concentration of grade a spermatozoa (highest motility) varied seasonally in both Denmark and Florida. The same trends were seen in both countries although the monthly variation in Orlando was not statistically significant. Thus, sperm quality (measured as the concentration of grade spermatozoa) was lowest during the winter months (October-March) and highest during the early summer (May-July). The mean monthly temperature had a significant effect on the concentration of grade a sperm in Denmark but not in Orlando. Even accounting for temperature, the pattern in both countries remained unchanged, and unexplained. Results presented from this study are not congruent with previous studies showing that sperm motility is lowest during summertime, nor that sperm motility decreases as the outdoor temperature rises. It is also clear that other environmental factors influenced the seasonal variation in sperm motility in this study, including lifestyle, where winter clothing or the reduction in outdoor activities in winter create a warmer environment for the testes during sperm production, as well as a lower exposure to daylight in winter. Limitations, reasons for caution With the large sample size (15,125 study participants), statistical controls for potential confounds, and consistent protocols for analysing ejaculates across years, city and country, this study eliminated the potential biases in the sampling and analyses that have made previous studies of seasonal variation in sperm quality difficult to interpret. Wider implications of the findings These findings have implications for male fertility and the selection of sperm donors, where motile-sperm concentration and motility are crucial criteria. The results indicate that seasonal variations might have affected the initial semen samples of donor candidates, who could have been accepted had they applied a different time of year. Trial registration number No
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".