Influence of Seasonal Variation on in Vitro Fertilization Success

Introduction: Several studies have yielded conflicting results regarding the influence of seasonal variation on in vitro fertilization (IVF) cycles outcome.

Aim: To evaluate the influence of seasonal variation on IVF outcome in a large cohort population.

Methods & Materials: A total of 5765 IVF cycles conducted in Sheba medical center between 2013 and 2016 were retrospective analyzed, of which 4215 and 1551 were fresh and frozen-thawed embryo transfers (FET) cycles, respectively. Cycles were assigned to seasons according to date of ovum pick up (OPU) for fresh embryo transfer cycles or according to the date of embryo thawing for FET cycles.

Results: There were no statistically significant differences between the calendar months or seasons concerning the number of oocytes retrieved or fertilization rate in the fresh cycles. Throughout the 4 years of the study, the monthly clinical pregnancy rate fluctuated between 18.2 and 27.9% per fresh embryo transfer (mean 23%) and between 18.2 and 29.4% per frozen-thawed embryo transfer (mean 23.3%). These fluctuations did not follow any specific seasonal pattern.

Conclusions: Our study did not demonstrate any significant influence of the calendar months or seasons on the clinical pregnancy rates of fresh or frozen-thawed embryo transfers. It might be speculated that the complete pharmaceutical control of the ovarian and endometrial functions, as well as the homogeneous treatment, procedures and laboratory equipment during the study period have lowered the influence of seasonal effect on fertilization treatment.