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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

Study question To develop an alternative fertility preservation method for young female cancer patients based on an ex vivo perfusion of whole ovaries serving as a platform for future ovarian stimulation studies. Summary answer It is possible to maintain viable follicles and to retrieve oocytes after ex vivo perfusion of ewe ovaries for up to 7 days. What is known already Some progress has been made in terms of follicular growth and the isolation of mature oocytes in vitro. However, full development, from early follicular stages to a viable offspring, has only been described in rodent models. The complex events controlling follicular expansion and the long time required for folliculogenesis and oocyte maturity in large mammalian species creating challenges and limitations for in vitro studies. Ex vivo perfusion of a whole ovary could potentially be a solution by exploiting the intact ovarian architecture to support folliculogenesis and oocyte maturation. Study design, size, duration Thirty-one ewe ovaries were divided into 4 groups and ex vivo perfused in a bioreactor. Group 1 (n = 14) perfusion for 48 hours with no hormone supplementation; Group 2 (n = 4) perfusion 96–101 hours with follicle stimulating hormone (FSH); Group 3 (n = 3) perfusion 120–168 hours with human menopausal gonadotropin (hMG); Group 4 (n = 10) perfusion 72–144 hours with hMG. Participants/materials, setting, methods Ewe ovaries from sexually mature ewes were ex vivo perfused in a bioreactor under normothermic conditions for up to 7 days (max total 168 hours). Histomorphological, immunohistochemical, hormonal and biochemical analyses were performed to assess ovarian structure and viability after cold ischemia and after perfusion which was subsequently compared to control ovaries. Main results and the role of chance The perfused ovaries in group 2 and 3 showed no significant differences in follicular density, viability and oocyte quality after ischemia and perfusion compared to control ovaries. Estradiol and progesterone levels did not increase during the perfusion. The perfused ovaries in group 1 and 4 showed a significant decrease in the ovarian reserve and oocyte quality. In total, 16 GV-MI oocytes were retrieved from groups 3 and 4. Limitations, reasons for caution 1. Ovaries were retrieved from ewes of unknown cycle and reproductive history. 2. The perfusion medium was changed after 24 hours from perfusion start to remove detrimental metabolites and this could affect the measured concentrations of hormones and metabolites in the perfusion medium. Wider implications of the findings: These results pave the way to propose ex vivo perfusion as a good platform for fertility preservation studies on whole mammalian and human ovaries to retrieve fully mature oocytes. Trial registration number Not applicable