Characteristics of Ovarian Hyperstimulation Syndrome During Pregnancy Resulting from Frozen-Thawed Embryo Transfer: A Case Report and Literature Review

Ovarian hyperstimulation syndrome (OHSS) is a rare complication often associated with superovulation cycles for fertility treatment. This report presents a case of spontaneous OHSS (sOHSS) during a frozen-thawed embryo transfer (FET) cycle, an event rarely documented in the literature. We describe herein the case of a 37-year-old nulligravida woman who presented with features suggestive of polycystic ovarian syndrome (PCOS), underwent FET using an artificial endometrial preparation protocol, and was transferred with two frozen-thawed blastocysts, which finally resulted in a diamniotic twin pregnancy. At the 12th week of gestation, the patient developed sOHSS with hyperthyroidism, which was successfully managed conservatively, and favorable outcomes were observed at delivery. This case contributes to the limited literature on sOHSS in FET cycles, reinforcing the importance of tailored monitoring and conservative management for optimal outcomes in such infertile patients.