Extreme ambient heat and outcomes of assisted reproduction in the continental United States, 1996 to 2018

Background: While extreme ambient heat has been associated with several adverse pregnancy and birth outcomes little is known regarding the link between extreme ambient temperatures and human fertility. Objective: To evaluate the associations between extreme ambient heat and assisted reproductive technology (ART) outcomes. Methods: Our analysis includes 1,087,379 patients in the continental United States who underwent 1,648,907 autologous oocyte, fresh embryo ART cycles reported to the National ART Surveillance System (1996–2018). Daily ambient temperature was derived by linking patient residential ZIP-code to a spatially refined gridded meteorology dataset. Three extreme heat metrics were created using different combinations of duration and intensity of hot days (mean daily temperature exceeding the ZIP-code-specific 98th percentile), as well as a continuous measure of temperature during folliculogenesis (90 days prior to cycle start) and ovarian stimulation. We estimated the adjusted odds ratio of cycle cancellation and live birth associated with extreme heat using generalized estimating equations, accounting for correlation within patients and clinics. Results: Extreme heat during folliculogenesis and ovarian stimulation had no or modest associations with cycle cancellation or live birth; however, there was significant heterogeneity by region. Patients in the West with ≥15 days of extreme heat during folliculogenesis had 21 % (confidence interval [CI] 5–41 %) greater odds of cycle cancellation and 28 % (CI 20–36 %) lower odds of live birth compared to patients with no extreme heat in that region. Most associations were null in other regions. Nationally, a 10 °F higher ambient temperature during folliculogenesis and ovarian stimulation was associated with a modest (1–2 %), but statistically significant, increased odds of cycle cancellation and decreased odds of live birth. Conclusions: We did not find strong evidence for an association between extreme ambient heat and ART outcomes.