Atypical presentation of severe ovarian hyperstimulation syndrome complicated by isolated pleural effusions: a case series and literature review

Pleural effusion as the predominant manifestation of severe ovarian hyperstimulation syndrome (OHSS) is rare and may occur with minimal or absent ascites. We present a recent retrospective case series from two UK centres describing presentation, investigations, management and outcomes of three patients developing large pleural effusions after medically assisted reproduction (MAR) in 2024-2025. All patients underwent antagonist stimulation with human chorionic gonadotropin (hCG) trigger and single fresh day-5 blastocyst transfer. Pleural effusions were diagnosed within a week of transfer, were predominantly right sided, and occurred despite modest ovarian enlargement and minimal or absent ascites. Patients required ultrasound-guided intercostal drainage with controlled outflow and albumin support. Pleural biochemistry was assessed in one case and this met 'Light's criteria' for exudate effusions. All patients improved rapidly after drainage and supportive management. Two pregnancies continued (one to term, one viable at 7 weeks), and one cycle did not result in pregnancy. In conclusion, pleural-predominant OHSS is a rare, yet recognisable phenotype. Early thoracic ultrasound, with careful interpretation of pleural biochemistry (including the serum-pleural albumin gradient in equivocal cases), avoidance of diuretics, selective albumin for intravascular support, timely ultrasound-guided drainage and venous-thromboembolism prophylaxis can optimise management. These cases also highlight the importance of preventive OHSS measures for future cycles.