The main risk of gonadotropins is ovarian hyper stimulation syndrome (OHSS). Ovarian hyper stimulation occurs in a small percentage of patients when too many follicles develop in the ovary. The ovary then grows to a large size and leaks fluids, resulting in nausea and bloating, dehydration, and, if severe, fluid collection around the abdominal organs, or ascites. In very severe cases, fluid collects around other organs, such as the lungs and heart, and blood clots and strokes can occur. If the ovary enlarges too much, rupture of the ovary and abdominal bleeding can occur. In rare cases, hospitalization and removal of abdominal fluid may be required to regulate fluid balance. In years past, fatalities have been reported, but are extremely rare.
Fortunately, serious cases of ovarian hyper stimulation are quite rare, and your doctor can predict and prevent hyper stimulation by monitoring the ovaries with ultrasound and blood estrogens levels. Removal of the granulosa cells during egg retrieval reduces the risk of hyper stimulation, so the risk with in vitro fertilization is lower than with gonadotropin use for simple ovulation induction. If the risk is very high, a cycle may be cancelled. Although this is a rare event, it provides complete safety, in that hyper stimulation almost never occurs after a cancelled cycle. If a cycle proceeds to egg retrieval, embryos may be frozen and saved for a later cycle, after the risk of hyper stimulation has subsided.
Multiple pregnancies are a risk when several embryos are transferred. Since several eggs will be retrieved from the ovaries and inseminated, multiple embryos are likely to develop. If multiple embryos are transferred into the uterus, twins, triplets, or even quadruplets or more could occur, perhaps requiring a selective reduction. Higher multiples are rare. In IVF, the risk of multiple pregnancies depends on the number and quality of embryos replaced; your doctor will estimate the risk of multiples for you. Some patients are not willing to accept any risk of multiple pregnancies and therefore elect to transfer fewer embryos, freezing the remainder for use in a later frozen transfer cycle. Your doctor will discuss this with you before the transfer.