Ovarian Hyperstimulation Syndrome: Causes and Treatment

Ovarian Hyperstimulation Syndrome


Ovarian hyperstimulation syndrome (OHSS) is a side effect of hormone medications that are taken to stimulate the ovaries to produce large numbers of eggs in women undergoing in vitro fertilization (IVF), ovulation induction, or artificial insemination. OHSS is usually caused by high doses of injectable hormone medications, but can also occasionally be caused by oral medications, such as clomifene (Clomid, Serophene). Sometimes it can even occur spontaneously although this is rare.


OHSS results in ovaries that are swollen and painful. In addition, mild-to-moderate OHSS can result in symptoms such as:

  • Mild-to-moderate abdominal pain
  • Diarrhea
  • Mild-to-moderate nausea and/or vomiting
  • Sudden weight increase of up to 6.6 pounds (3 kilograms)
  • Abdominal bloating or increased waist size

Severe OHSS can result in symptoms such as:

  • Shortness of breath
  • Rapid weight gain of up to 33 to 40 pounds (15 to 20 kilograms)
  • Severe persistent nausea and vomiting
  • Severe abdominal pain
  • Reduction in frequency of urination
  • Tight or enlarged abdomen

You should see your doctor if you suspect you have OHSS, even if the symptoms appear to be quite mild. If you develop pains in your legs or shortness of breath you should seek medical attention straight away.

Although the specific cause of OHSS isn’t fully understood, one main contributing factor seems to be high levels of human chorionic gonadotropin (HCG), a hormone produced naturally in pregnancy but which is also administered as a trigger in fertility treatments so the mature follicles in your ovary will each release an egg. Ovarian blood vessels react abnormally to HCG and begin to leak fluid. This fluid then swells the ovaries, and occasionally enters the abdomen in large amounts.3 OHSS usually happens within the week following an injection of HCG and if you become pregnant from the fertility treatment, OHSS may worsen as your body starts to make its own additional HCG.

Who is at risk?

Women most at risk of OHSS have one or more of the following risk factors:

  • Low body weight
  • Under 30 years of age
  • Large number of follicles
  • Previous OHSS episodes
  • High or sharply increasing levels of estradiol (estrogen) before the HCG trigger shot is given
  • Polycystic ovary syndrome (PCOS)*,


Severe OHSS can lead to life-threatening complications in approximately 1 to 2 per cent of women undergoing ovarian hyperstimulation, such as:

  • Pregnancy loss (from miscarriage or a necessary abortion due to complications)
  • Kidney failure
  • Electrolyte (such sodium or potassium) disturbances
  • Rupture of a cyst in the ovary which can lead to serious bleeding
  • Twisting of an ovary (ovarian torsion)


In order to prevent OHSS, your doctor should individualize your treatment plan and monitor you carefully throughout your treatment cycle. Monitoring should include frequent ultrasounds to check the size and number of follicles and blood tests to check hormone levels.

Some strategies used to avoid OHSS include:

  • Reducing or adjusting the treatment dose
  • Giving women with PCOS metformin during the treatment cycle
  • Coasting, whereby the patient waits a few days longer to receive the HCG trigger due having estrogen levels being high or a large number of developing follicles
  • Using a different type of medication than HCG for the trigger shot, such as leuprolide/leuprorelin (Lupron)
  • Freezing all the embryos, if doing an IVF cycle, and transferring them in another treatment cycle – either a natural menstrual cycle or one in which estrogen is used to thicken the uterine lining


With no treatment OHSS usually resolves within a week if caused by medication, or within two or more weeks if caused by becoming pregnant. Treatment for OHSS aims to alleviate symptoms and reduce ovarian activity.

Mild OHSS does not usually require treatment and treatment for moderate OHSS may include:

  • Anti-nausea medication
  • Prescription pain relief
  • Drainage of excess abdominal fluid
  • Adequate fluid intake

Patients with moderate OHSS need to also undergo frequent physical exams and ultrasounds as well as daily weigh-ins and waist measurements to check for large changes in weight. Blood tests are also performed to monitor problems such as dehydration and electrolyte imbalance and the amount of daily urine is measured. In addition, support stockings should be worn in order to prevent blood clots.

If you have severe OHSS you may need to go to the hospital in order to be monitored closely and to undergo more aggressive treatment such as intravenous administration of fluids. Ovarian activity may be suppressed with a certain type of medication called gonadotropin-releasing hormone antagonists and you may be given anticoagulants to reduce the risk of developing a blood clot. Occasionally surgery is required for a ruptured ovarian cyst or you may need to undergo intensive care if you are experiencing liver or lung complications.

*PCOS is a common reproductive disorder that is associated with irregular menstruation, excessive hair growth and a large number of follicles on each ovary.

Melody Watson
Melody Watson holds Bachelors degrees in Biochemistry and Microbiology. She works as a medical writer for a medical communications agency in Berlin, Germany, where her work ranges from medical translation to writing publications for medical journals. Melody is passionate about promoting science, including evidence-based medicine, and debunking pseudoscience.

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