SUMMARY OBJECTIVE: This study aimed to evaluate the prevalence of ovarian hyperstimulation syndrome (OHSS) and associated risk factors in patients undergoing fertilization cycles at risk of OHSS (≥15 antral follicles or ≥15 oocytes aspirated) and submitted to cryopreservation of all embryos in the Human Reproduction Service of the Pérola Byington Hospital (Referral Center for Women's Health) in São Paulo, SP, Brazil. METHODS: This cross-sectional, institutional, descriptive study of secondary data from patients’ charts enrolled in the Assisted Reproduction Service of the Pérola Byington Hospital at risk of OHSS after controlled ovarian stimulation and submitted to cryopreservation of all embryos was conducted between January 2015 and September 2017. RESULTS: OHSS occurred in 47.5% of cycles, all with mild severity, and there were no moderate or severe cases of OHSS. CONCLUSION: The cryopreservation of all embryos is associated with a reduction in moderate and severe forms of OHSS. Risk factors for OHSS should be evaluated prior to initiation of treatment, with less intense stimulation protocols accordingly.

SUMMARY OBJECTIVE: The aim of this study was to compare the use of micronized vaginal progesterone and oral dydrogesterone in the endometrial preparation for frozen-thawed embryo transfer. METHODS: This was a randomized, controlled, open, two-armed clinical trial, with women undergoing frozen-thawed embryo transfer along with hormone replacement therapy for endometrial preparation, between September 2019 and February 2021. A total of 73 patients were randomly selected and orally administered 40 mg/day dydrogesterone (dydrogesterone group, n=36) or 800 mg/day micronized vaginal progesterone (micronized vaginal progesterone group, n=37), after endometrial preparation with transdermal estradiol. The main outcome was a viable ongoing pregnancy with 12 weeks of gestation as evaluated by ultrasound. RESULTS: The reproductive outcomes in frozen-thawed embryo transfer cycles were similar, with pregnancy rates in the dydrogesterone and micronized vaginal progesterone treatment groups being, respectively, 33.3 and 32.4% at 12 weeks pregnancy (confidence interval= -22.4-20.6, p=0.196). CONCLUSIONS: The use of oral dydrogesterone may be a more patient-friendly approach to endometrial preparation in frozen-thawed embryo transfer cycles, avoiding undesirable side effects and discomfort resulting from vaginal administration, while also providing similar reproductive results.