Hello again to everyone, today I am bringing to you the topic of Ovarian Hyperstimulation Syndrome (OHSS). Here you will read about the definition of OHSS, the causes and risks. You will see why OHS is what every good doctor strives to avoid, and of course, what every patient would like to avoid as well.

I would like to start by saying that you will read some things that may be frightening, because the most severe forms of OHSS can lead to significant medical problems. However, OHSS does not occur with great frequency and the severe forms are very rare. The next blog will review ways to lower the risks. In many cases it is preventable, although even when your doctor is very careful, OHSS can still occur.

OHSS occurs as a result of taking fertility drugs. These cause the ovaries to become larger than normal and to leak fluid. The more eggs that are produced in the cycle, the higher the risk of OHSS. The leaking fluid can cause significant abdominal swelling, and some of the fluid could make its way to the lungs. We will get back to these and other problems with OHSS in a bit.

OHSS, except for some very rare instances, can only be caused by fertility drugs. When we use infertility drugs, clomid or the injectables, we are hyperstimulating the ovaries. The goal of fertility treatment is to get the ovaries to make more eggs per month than usual. Sometimes we use the drugs to try to just make one egg, but usually we are going for more. In fact,therapy with any of these drugs is called Controlled Ovarian Hyperstimulation. Controlled is the key word. Therefore we expect all women receiving fertility drugs to have enlarged ovaries with the possibility of a small amount of fluid leaving the ovaries, and some cramping. When Controlled Ovarian Hyperstimulation becomes less controlled, OHSS can result.

The development of OHSS through the use of clomid is quite rare, but it has been known to occur. However,the injectables (examples are Follistim, Gonal-F, Menopur, Bravelle) pose much more of a threat. Clomid is a very different drug than the injectables. Clomid nudges along the normal ovulation process by getting the brain (actually the pituitary gland) to put out a little extra FSH. Because there is only so much FSH stored in the pituitary, usually 1-3 eggs will ovulate, as opposed to the one egg that ovulates when no drugs are used. For almost all women, this is not enough stimulation to cause OHSS. The injectables, on the other hand, are more powerful. They are FSH (sometimes with a bit of LH), and more FSH is delivered to the ovaries than in a natural cycle or with Clomid. The injections directly stimulate the ovaries to develop a larger number of eggs for ovulation. Because more eggs are produced, the injectables carry a higher risk of OHSS.

Who is at risk for OHSS? Women who are most likely to make a high number of eggs. The first and obvious group is younger women. For better or for worse, young women have more eggs, and develop more eggs for ovulation when given the injectables. Women with polycystic ovaries (PCO) are at higher risk for OHSS. This is because women with PCO have a very large number of eggs. These eggs are in follicles that have reached the stage just prior to entering the ovulation process. The fertility drugs can get many of these “almost ready” eggs to come up at once. And there are the exceptions, women who do not have risk factors, yet hyperstimulate when exposed to drug.

The severity of OHSS varies widely. Most textbooks divide the various degrees into mild, moderate and severe. Mild does not cause medical problems but may cause a woman to take notice of the changes in her body. In the mild form, the ovaries produce a few eggs and as a result have enlarged slightly. The ovaries have released some fluid, which the patient perceives as bloating. Cramping is mild. Many women have mild hyperstimulation, however they are not at all bothered by the symptoms and they go about business feeling no need to contact a physician for evaluation. The majority of women who take the injectable medications fall into this category. Some women with the same degree of mild hyperstimulation, are more bothered and concerned and may let us know that they do not feel well. Like many things in medicine, we can’t explain why 2 women with the same number of eggs and the same amount of fluid around the ovaries feel differently.

The two worse forms of OHSS are moderate and severe. In these cases, the problems are more complex than just large ovaries and a bit of fluid in the pelvis. In these cases, the OHSS can affect other areas of the body. Dehydration comes into play, and can be very problematic. This occurs as the ovaries leak larger amounts of fluid. The abdomen becomes noticeably distended. Women gain weight as the tummy accumulates more and more fluid. This probably doesn’t sound like dehydration to you, but it is. What’s happening is the leaking fluid comes from the blood which is circulating through the ovaries. As more fluid leaks out, less is fluid is in the blood and the blood becomes thicker, thus the dehydration. Not only does the blood lose water, but with the water flows sodium, so in the blood, sodium levels are low. Proper levels of sodium are necessary for normal function of the brain.

As the blood becomes more concentrated, levels of clotting factors increase. Clotting factors are proteins that are necessary for us to prevent excessive bleeding when injured; they make the blood clot. If the levels of these proteins get too high, the blood will be more likely to clot without any injury. For instance, clots can occur spontaneously in the legs, arms,neck and lungs. The worse the OHSS, the greater the risk if blood clotting.

OHSS can have a big effect on the kidneys. As the dehydration progresses, the overall volume of the blood decreases. Good blood volume is necessary for the normal kidney function of cleaning the blood. Decreased blood volume means that less blood is getting to the kidneys, and therefore the kidneys have trouble doing their job. The blood cannot be cleared of its waste, which is bad for the body.

OHSS has an effect on the lungs. The sheer volume of fluid in the abdomen can make breathing a problem for a couple of reasons. The first has to do with the pressure that builds in the chest as the abdomen fills. We’ve all heard that we breathe with our diaphragm, which is true statement. The abdominal fluid pushes up putting pressure on the diaphragm, making it harder to freely breathe in and out. The second problem has to do with fluid getting into the lungs. When the abdomen gets packed with fluid, it can squeeze through the diaphragm, into the spaces around the lungs. A small amount of fluid around the lungs is tolerable, but larger amounts make it harder to breathe and can cause chest pain.

If you have never taken these drugs, I do not want this blog to discourage you from taking the medicine you may need. If you have any concerns, talk to your doctor about the possible side effects and complications of these medications.
Next time we will discuss ways to prevent and treat OHSS.

Thanks for reading and don’t forget disclaimer 5.17.06.

Dr. Licciardi


  • Ovarian hyperstimulation syndrome. Practice Committee of American Society for Reproductive Medicine. Fertil Steril. 2008 Nov;90(5 Suppl):S188-93.
  • Grossman LC, Michalakis KG, Browne H, Payson MD, Segars JH. The pathophysiology of ovarian hyperstimulation syndrome: an unrecognized compartment syndrome. Fertil Steril. 2010 Sep;94(4):1392-8.
  • Mullin CM, Fino ME, Reh A, Grifo JA, Licciardi F. Symptomatic isolated pleural effusion as an atypical presentation of ovarian hyperstimulation syndrome. Case Rep Obstet Gynecol. 2011; 2011:967849.