Seasonal effects on ivf-icsi-pgta cycle outcomes: a retrospective multi-center study

To study seasonal effects on oocyte retrieval and subsequent FET outcomes in different US geographical locations. SART data of 8 ART centers from reporting years 2018 to 2021 were included in this retrospective multi-center study. 12,804 consecutive IVF-ICSI-PGT cycles were analyzed. Mean age at cycle start was 36.3 (range 21-45 y/o) were analyzed. Cycles using donor oocytes were excluded. Oocyte retrievals performed during a 90-day period with coldest daily average temperature (T) or shortest clear-daylight hours (D) were compared to a 90-day period with warmest T or longest D, respectively. There are some unique climate zones in the US: states like CA and AZ are usually warm all year round. However, states in Midwest as well as WA, have distinctive seasonal changes. Therefore, three geographical areas were selected: California and Arizona in the Southwest (SW, 2198 cycles), with seasonal variations from mean T and from mean D of 46% and 92%, respectively; Washington and Oregon in the Northwest (NW, 4401 cycles), with seasonal variations from mean T and mean D of 54% and 304%, respectively; and Illinois, Ohio, and Virginia in the Midwest (MW, 6205 cycles), with seasonal variations from mean T and mean D of 151% and 158%, respectively. The numbers of oocytes retrieved and fertilized, usable blastocyst rates, euploid rates, and rates of implantation, clinical pregnancy and live birth in subsequent FETs were compared by Duncan’s t-test or Chi-squared test. The T and D data were retrieved from www.weather.gov. The study was approved by Pinnacle Research Ethics Committee. The numbers of oocytes retrieved and fertilized, usable blastocyst rates, and euploid rates were comparable within each geographical location between the coldest and warmest T periods and between longest and shortest D periods. The rates of implantation (61% vs 55%), clinical pregnancy (58% vs 52%) and live birth (54% vs 48%) in subsequent FETs were all significantly higher in the warmest T period than in the coldest period in MW (p<0.05), while there were no significant differences in SW or NW. The rates of implantation (60% vs 49%), clinical pregnancy (57% vs 47%) and live birth (53% vs 43%) in subsequent FETs were significantly higher in longest D period than in shortest D period in NW (p<0.05) but were similar in the other two regions. This is the first multi-center study to investigate seasonal effects on ART outcomes in different geographical locations while using only euploid embryos for transfer. The present study is novel in that it demonstrates that seasonal effects on ART outcomes are dependent on the magnitude of seasonal variations in specific geographical location. This may explain the controversy in previously reported studies from different regions. Further prospective studies may be needed to better understand these phenomena.