O-016 Sperm motility has declined between 2017 and 2022 among candidate sperm donors in Denmark
Authors: Montgomerie R , Lassen E , Skytte A B , Pacey A 
Published: June 2023

Study question

Has sperm quality among candidate sperm donors in Denmark changed in recent years (2017-2022)?

Summary answer

Although sperm concentration of candidate donors did not change, sperm quality (motility) declined by ∼35% after controlling for age and other potential confounds.

What is known already

Questions remain about whether human sperm quality has declined in recent decades. Whilst some studies support this trend, others dispute it due to potential biases in the populations studied or the different methodological approaches to measuring sperm quality. Resolution of this issue is important because of the implications for human fertility, as well as for those involved in the recruitment of donors for use in Medically Assisted Reproduction.

Study design, size, duration

We analyzed the semen quality of 6,774 candidate sperm donors attending for their first semen analysis at Cryos International from 2017 to 2022 at four cities in Denmark: Aarhus, Aalborg, Copenhagen, and Odense. We analyzed only the first sperm sample, whether or not the candidate was eventually accepted as a donor. All donor candidates were between 18 and 46 years old and lived in or near these four cities.

Participants/materials, setting, methods

Ejaculates were examined within one hour of production. Semen volume (mL) was estimated by weight and both total sperm concentration (106/mL) and the concentration of grade A and B spermatozoa were measured using the same protocols and CASA-system across all years at each site. Analyses were controlled for age, site, ejaculate volume, and the average monthly temperature when the ejaculate was produced. We used longitudinal data from accepted donors to test for methodological biases.

Main results and the role of chance

From 2017 to 2022, there was no evidence of changes in either semen volume (median = 3.5 mL) or sperm concentration (median = 58 million/mL) in the ejaculates of candidate donors. There was, however, clear evidence of a decline in the concentration (and total number) of grade A and B motile sperm. For the average candidate sperm donor that we studied, the concentration of grade A sperm declined from 5.15 [95% CL: 4.18, 6.34] million/mL in 2018 to 3.33 [2.71, 4.08] million/mL in 2022. This corresponds, for example, to a predicted decline in sperm quality of ∼35% for a 25-year-old candidate from Aarhus in a month when the average daily high temperature was 18.5 °C. The same pattern was evident from all four cities, but candidates at Aarhus had lower overall sperm quality (grade A sperm motility) than candidates at the other three cities. Analysis of the longitudinal data from repeated donations from all 'accepted' donors during this same period (2017 – 2022), allowed us to rule out methodological factors (sperm collection, CASA, statistical anomalies) that might have influenced these findings.

Limitations, reasons for caution

We cannot rule out the possibility that men with poor sperm quality were more likely to apply to be donors during the global pandemic, or that the lifestyles of candidate donors had changed during this period because of lockdowns or changes in work patterns.

Wider implications of the findings

Candidate sperm donors are a useful population in which to monitor changes in human semen quality over time. The results may have implications for human fertility and the recruitment of sperm donors, where motile sperm concentration is an essential selection criterion.

Trial registration number

not applicable