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Ovarian Hyperstimulation Syndrome

Adapted from Fact Sheet by The American Society for Reproductive Medicine.

What is Ovarian Hyperstimulation Syndrome?

Ovarian hyperstimulation syndrome (OHSS) is an exaggerated response to taking the medicines used to make eggs grow.

OHSS is characterized by enlarged ovaries and fluid accumulation in the abdomen. A mild form occurs in 10% to 20% of In Vitro Fertilization cycles and results in some discomfort but usually resolves quickly without complications. The severe form occurs approximately 1% of the time.

The hallmark of OHSS is an increase in capillary permeability resulting in fluid leaking into the abdomen. This can cause bloating, nausea, and swelling of the abdomen. When OHSS is severe, blood clots, shortness of breath, abdominal pain, dehydration, and vomiting requiring hospitalization and intensive care are possible.

Mild manifestations of OHSS include:

  • Transient lower abdominal distention and discomfort
  • Mild nausea
  • Vomiting
  • Diarrhea


Onset of symptoms typically occurs soon after oocyte retrieval, but it may be delayed. These symptoms usually go away without treatment within a few days.

Severe OHSS includes:

  • Sudden onset of abdominal pain
  • Significant abdominal swelling
  • Difficulty breathing
  • Continued vomiting or nausea
  • Difficulty tolerating fluids
  • Decreased urination
  • Weight gain of over 3 pounds in 2 days


Which factors increase the risk for developing OHSS?

The following factors increase the risk for developing OHSS:

  • Large number of growing follicles along with high estradiol (estrogen, E2) levels.
  • Young age
  • History of polycystic ovary syndrome (PCOS)
  • High or rapidly rising serum estradiol levels
  • High antral follicle count (25 or more)
  • High number of medium size follicles developing during ovarian stimulation
  • If you become pregnant, the pregnancy will increase the likelihood, duration, and severity of OHSS symptoms.


How is OHSS treated?

The OHSS condition is temporary, usually lasting only a week or two and will typically self-resolve.

  • Drinking lots of electrolyte-rich fluids (over 120 ounces per day) are recommended.
  • Medicines for pain and nausea are available.
  • Strenuous physical activity should be avoided.
  • Strict bed rest is unwarranted and may increase risk of blood clots.
  • Light physical activity should be maintained to the extent possible.
  • Full-length venous support stockings are recommended.
  • A medicine called cabergoline can reduce the fluid accumulation.
  • If there is excessive fluid in the abdomen, drainage of fluid can provide significant relief. On occasion, more than one drainage is helpful.
  • Avoiding immediate pregnancy by freezing (cryopreserving) embryos and transferring them at a later date may be required.
  • When symptoms of OHSS emerge even before administration of hCG, cycle cancellation may be required.
  • There is rarely a need for hospitalization.


What other complications occur with severe OHSS?

Complications from OHSS can be severe. Patients may become dehydrated and pressure in the abdomen may increase from too much fluid. These problems can lead to blood clots forming within the blood vessels. Blood clots can travel to lungs or to other important organs. This can be potentially life-threatening.

These complications can usually be avoided by recognizing the signs and symptoms that OHSS is getting worse and getting appropriate treatment.

How long does it take for OHSS to get better?

OHSS symptoms usually appear a few days after oocyte retrieval and usually resolve within two weeks, unless pregnancy occurs. Pregnant women often continue to have symptoms for 2-3 weeks or more after a positive pregnancy test. The symptoms gradually go away, and the rest of the pregnancy is not affected.

Is there anything that can reduce the risk of having OHSS?

Pregnancy can make OHSS worse or last longer. If a woman develops OHSS, avoiding immediate pregnancy by freezing her embryos for transfer at a later time can help the OHSS resolve more quickly and keep it from progressing.

February 2016


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