Ovarian hyperstimulation syndrome (OHSS) is a medical condition that can occur in some women who take fertility medication to stimulate egg growth, and in other women in very rare cases. Most cases are mild, but rarely the condition is severe and can lead to serious illness or death. Signs and symptoms Symptoms are set into 3 categories: mild, moderate, and severe. Mild symptoms include abdominal bloating and feeling of fullness, nausea, diarrhea, and slight weight gain. Moderate symptoms include excessive weight gain (weight gain of greater than 2 pounds per day), increased abdominal girth, vomiting, diarrhea, darker urine, decreased urine output, excessive thirst, and skin and/or hair feeling dry (in addition to mild symptoms). Severe symptoms are fullness/bloating above the waist, shortness of breath, pleural effusion, urination significantly darker or has ceased, calf and chest pains, marked abdominal bloating or distention, and lower abdominal pains (in addition to mild and moderate symptoms). Complications OHSS may be complicated by ovarian torsion, ovarian rupture, venous thromboembolism, acute respiratory distress syndrome, electrolytes imbalance, thrombophlebitis and chronic kidney disease. Symptoms generally resolve in 1 to 2 weeks, but will be more severe and persist longer if pregnancy occurs. This is due to human chorionic gonadotropin (hCG) from the pregnancy acting on the corpus luteum in the ovaries in sustaining the pregnancy before the placenta has fully developed. Typically, even in severe OHSS with a developing pregnancy, the duration does not exceed the first trimester. Cause Sporadic OHSS is very rare, and may have a genetic component. Clomifene citrate therapy can occasionally lead to OHSS, but the vast majority of cases develop after use of gonadotropin therapy (with administration of FSH), such as Pergonal, and administration of hCG to induce final oocyte maturation and/or trigger oocyte release, often in conjunction with IVF. The frequency varies and depends on a woman's risk factors, management, and methods of surveillance. About 5% of treated women may encounter moderate to severe OHSS. Risk factors include polycystic ovary syndrome, young age, low BMI, high antral follicle count, the development of many ovarian follicles under stimulation, extreme elevated serum estradiol concentrations, the use of hCG for final oocyte maturation and/or release, the continued use of hCG for luteal support, and the occurrence of a pregnancy (resulting in hCG production). Mortality is low, but several fatal cases have been reported. Medications Ovarian hyperstimulation syndrome is particularly associated with injection of a hormone