Exposure to ambient temperature extremes during peri-conception and fecundability

Background and Aim: Ambient temperature extremes, particularly high heat, have been associated with adverse pregnancy outcomes; however, fecundity has been little examined. We assessed the relationship of exposure to ambient temperature extremes during the menstrual cycle with fecundability. Methods: A total of 1,228 women enrolled in the EAGeR trial at study sites in Salt Lake City, Denver, Buffalo, and Scranton, United States. Analyses evaluated exposure to ambient temperature, obtained from local weather monitors during the first two menstrual cycles of follow-up, and pregnancy, assessed at the end of each menstrual cycle using urinary hCG. Mean daily temperature and hours per day above and below set thresholds (≥20°C, ≥25°C, ≥30°C, and <0°C) were calculated during the follicular phase (menses through ovulation), luteal phase (ovulation through next menses), ovulation (-5 to 0 days before ovulation), and implantation (6 to 10 days post-ovulation). Cox proportional hazards models calculated the fecundability odds ratio (FOR). Models were stratified by warm (Apr. 1-Sep. 30) versus cold (Oct. 1-Mar. 31) season and adjusted for participant characteristics. Results: A total of 2,147 cycles were observed. During the warm season, a 2°C increase in temperature across the menstrual cycle was associated with a trend of lower fecundability, though estimates were imprecise. Each additional hour per day of temperatures ≥30°C during ovulation and implantation was associated with lower fecundability (FOR 0.86, 95% CI 0.73-1.00 and FOR 0.89, 95% CI 0.78-1.01, respectively). During the luteal phase, overnight (10pm-6am) temperatures ≥25°C were most strongly associated with lower fecundability as compared to daytime temperature extremes (FOR 0.52, 95% CI 0.28-0.98 for each additional hour per night ≥25°C). No clear associations were observed during the cold season. Conclusions: Exposure to high temperatures ≥30°C during ovulation and implantation and overnight temperatures ≥25°C during the luteal phase may reduce chance of pregnancy. Keywords: Temperature, Pregnancy, Fecundability