Abstract
Abstract Study question Is there a seasonal influence on fresh in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) treatment outcomes? Summary answer Season does not seem to affect live birth rate, clinical pregnancy rate or miscarriage rate after fresh IVF/ICSI treatment. What is known already Seasonal variations in human natural conception and birth rates are well described. However, the impact of seasonal variation on IVF outcomes has not yet been clarified and conflicting reports have been published. Study design, size, duration Nationwide, register-based cohort study including all first time fresh IVF/ICSI treatments (n = 52 788) leading to oocyte pick up (OPU) in Sweden between 2009 and 2018. Participants/materials, setting, methods First time fresh IVF/ICSI cycles leading to OPU were identified in the National Quality Registry of Assisted Reproduction (Q-IVF). Data collected included patient characteristics, information about the treatment cycle and pregnancy outcome. The patients were divided into season subgroups based on the date for OPU. The primary outcomes of the study were live birth per OPU and per embryo transfer (ET), clinical pregnancy per ET and miscarriage per clinical pregnancy. Logistic regression was performed. Main results and the role of chance The impact of seasons on the outcome of first time fresh IVF/ICSI cycles leading to OPU was assessed. A statistically significant overall seasonal influence was seen on live birth rate per OPU in the unadjusted analysis (p =0.036), where cycles performed in summer showed lower live birth rate (OR 0.92, 95% CI 0.87-0.97, p =0.004) compared with the other seasons. After adjustment for relevant confounders the overall impact of seasons on live birth rate was no longer statistically significant (p =0.10). Although post-hoc analyses still showed lower live birth rate in summer compared with the other seasons (OR 0.93, 95% CI 0.88-0.99, p =0.019). The impact of seasons on clinical pregnancy rate, miscarriage rate and live birth rate was further assessed through the analysis of the first cycles where ET was performed. No overall statistically significant seasonal influence was seen on clinical pregnancy, miscarriage and live birth rates after adjustment for confounders. Limitations, reasons for caution Possible limitations are the retrospective design of the study and the lack of adjustment for other important confounders i.e. cause of infertility, not included in Q-IVF. Wider implications of the findings This large cohort study shows a lack of seasonal influence on live birth-, clinical pregnancy- and miscarriage rate after fresh IVF/ICSI treatment. In the clinical setting, season should not be taken into consideration when planning and performing fresh IVF/ICSI. Trial registration number non applicable
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