Wildfire smoke exposure is associated with decreased sperm concentration and total motile sperm count

To examine the impact of smoke exposure on semen analysis parameters of intrauterine insemination (IUI) patients in the greater Seattle, Washington area, as wildfire becomes more prevalent. We hypothesized that wildfire smoke exposure was associated with a decline in total motile sperm count.

Retrospective cohort study.

Patients undergoing fertility treatments at the University of Washington from 2018 to 2022.

Subjects were exposed to seasonal wildfire events in the fall of 2018, 2020, and 2022. Pre-exposure semen was a diagnostic fresh sample before each respective wildfire event, whereas post-exposure semen was taken at the time of IUI during the wildfire smoke exposure windows. All subjects acted as their own controls in a paired pre-post analysis.

Primary outcome measure was total motile sperm count; secondary outcome measures were semen volume, sperm concentration, total sperm count, total progressively motile sperm count, percent motile sperm, percent progressively motile sperm.

Eighty-four subjects were identified who underwent IUI across the 2018 (n = 27), 2020 (n = 30), and 2022 (n = 27) wildfire smoke events. Median time between initial semen analysis and semen analysis for IUI was 4 months. We observed a decline in sperm concentration, total sperm count, total motile sperm count, and total progressively motile sperm count. We also observed an increase in percent progressively motile sperm. These trends did not differ across event years.

Our results are consistent with a prior small study demonstrating that wildfire smoke exposure is associated with declines in sperm quality. These findings highlight the need for further research on the effects of wildfire smoke exposure on human sperm and fertility treatments, especially as smoke exposures are expected to increase with climate change.