Ovarian hyper-stimulation syndrome (OHSS) is the most common serious complication of the injectable fertility medications occurring in 2-3% of IVF and FSH/IUI cycles. The syndrome results from ovarian enlargement with ovulation of multiple follicles and accumulation of large quantity of fluid within the abdomen. The symptoms include distension, nausea, pain and shortness of breath.
The severity of OHSS varies widely. Mild degree of abdominal distension occurs in virtually all women given gonadotropin injections. Young age, presence of PCOS (What is PCOS?), development of many small follicles, small body habitus and high levels of estradiol are among the major predisposing factors towards moderate and severe forms of OHSS. Mild and moderate OHSS frequently respond to bedrest and supportive measures. Severe cases may require a minor operation to drain excess fluid from the abdominal cavity, intravenous fluids and even hospitalization. The severe OHSS may lead to such life-threatening complications as formation of clots, stroke, kidney failure and pulmonary embolism.
There are two types of severe OHSS: 1. early which occurs in response to hCG trigger within 5-7 days of ovulation; 2. late which is caused by the rising hCG hormone levels produced by the placenta in conception cycles. Over the years many strategies have been developed to prevent the occurrence of severe OHSS but most of them are not always effective. The single best technique to avoid early severe OHSS is to substitute LH trigger for hCG trigger while the single best strategy to eliminate the risk of late severe OHSS is to freeze all the embryos and delay the embryo transfer till the next cycle. Other approaches include reduction in dose of hCG trigger, “coasting” to allow estradiol levels to fall, administration of volume expanders during egg retrieval and cycle cancellation before hCG.
Avoidance of severe OHSS has become a major goal at the Alta Bates IVF program and it plays a major role in selecting the individualized stimulation protocol for each patient. Combination of close monitoring of ovarian response, use of LH to trigger ovulation and the strategy of freezing of all fertilized eggs for transfer in the subsequent cycle have allowed us to eliminate all cases of severe OHSS in IVF patients over the past 3 years.