Ambient temperature in relation to ovarian reserve and early outcomes following ovarian stimulation and in vitro fertilization.

Introduction: There is limited epidemiologic evidence on the associations between ambient temperature and early outcomes of in vitro fertilization (IVF). This study examined the association between ambient temperature exposures during spermatogenesis in males and folliculogenesis in females with early IVF outcomes.

Methods: This retrospective cohort study included 529 oocyte donors linked to male partners of 1154 recipient couples who underwent 1379 oocyte thaw cycles between 2008 and 2020 at an IVF clinic in Atlanta, Georgia, USA. Daily ambient mean (T), minimum (T), maximum (T), and apparent temperature (T) estimated at a 4 km resolution were linked to donor and recipient addresses and then averaged during folliculogenesis, controlled ovarian stimulation, and spermatogenesis. We used generalized estimating equations to estimate effect estimates (per interquartile range [IQR] increase) and 95% confidence intervals (95% CI) for the associations between average ambient temperature exposures in relation to ovarian reserve, oocyte yield, and proportion of oocytes surviving thaw, oocytes fertilized, and useable embryos.

Results: Higher ambient temperature exposures during folliculogenesis and ovarian stimulation generally had negative, though imprecise, associations with oocyte yield (% change in total oocytes retrieved per IQR increase in mean temperature = -6.9% 95% CI -18.5,6.3). Higher temperature exposures during folliculogenesis (aOR = 1.85 95% CI 1.16, 2.95) and ovarian stimulation (aOR = 2.14 95% CI 1.44, 3.19) were associated with higher oocyte survival and higher T during ovarian stimulation was associated with higher oocyte fertilization (aOR = 1.27 95% CI 1.01, 1.59).

Conclusions: Higher ambient temperature exposure during follicular development was positively associated with oocyte survival and fertilization. These findings highlight the reproductive health implications of increasing global average temperatures, though more research is needed to clarify these associations.