Spontaneous Ovarian Hyperstimulation Syndrome in a Naturally Conceived Singleton Pregnancy With Familial Predisposition: A Case Report.

Spontaneous ovarian hyperstimulation syndrome (sOHSS) is an uncommon condition that can occur in naturally conceived pregnancies and may present a significant diagnostic challenge because its clinical and radiological features can resemble ovarian malignancy. We describe the case of a 30-year-old primigravida who presented in early pregnancy with abdominal pain and was found to have bilateral multicystic ovarian enlargement, ascites, and a markedly elevated cancer antigen-125 (CA-125) despite a viable singleton pregnancy conceived without fertility treatment. A detailed history revealed a strong familial pattern of sOHSS, raising suspicion of an inherited predisposition. Following multidisciplinary assessment, she was managed conservatively with close clinical, biochemical, and ultrasound surveillance, resulting in progressive resolution of ovarian enlargement and ascites with an ongoing uncomplicated pregnancy. This case highlights the importance of recognizing sOHSS as a differential diagnosis in natural conception pregnancies, obtaining a thorough family history, and adopting an appropriate multidisciplinary approach to avoid unnecessary intervention while achieving favorable maternal and fetal outcomes.