For COVID-19 and vaccination updates, view our information for the community. If you're experiencing symptoms, call your primary care provider.

Understanding Ovarian Hyperstimulation Syndrome

If you’re undergoing fertility treatment or at least considering it, you know how daunting the process can be. While the pregnancy rates associated with treatment are promising, rare complications can occur – one of them being ovarian hyperstimulation syndrome (OHSS). 

OHSS, a condition characterized by ovarian enlargement with or without abdominal distension and discomfort, occurs when a woman’s ovaries over-respond to fertility medication designed to induce egg development (controlled ovarian stimulation). Symptoms can include:

  • Nausea and/or vomiting
  • Abdominal bloating
  • Fluid buildup in the pelvis or abdomen
  • Rapid weight gain
  • Shortness of breath
  • Diminished kidney function
  • Decreased urine output
  • Blood abnormalities and clots

Before embarking on treatment, here’s what you need to know about OHSS:

Severe OHSS is rare

Less than half (33%) of fertility treatments utilizing injectable medications are complicated by mild OHSS, which includes ovarian enlargement and abdominal discomfort with or without nausea or vomiting.

Moderate OHSS occurs in 3 to 4% of cycles and is similar to mild OHSS with the addition of the ascites (fluid in the pelvis and abdomen).

The treatment for mild and moderate OHSS is generally supportive. Patients should rest, stay hydrated and monitor their weight and urine output.

Patients with severe OHSS, which occurs in 0.1 to 0.2% of cycles, may experience rapid weight gain, decreased urine output and severe abdominal pain. Blood clots in the legs are a rare complication.

Severe OHSS usually warrants a trip to the hospital for monitoring and IV fluids. In some cases, anticoagulation medication may be prescribed and paracentesis – or aspiration of pelvic or abdominal fluid – may be necessary.

Keep in mind that OHSS is virtually unheard of when oral fertility medications are used.


Incidence has dramatically decreased over the years

Because many providers now recommend the less risky Lupron trigger shot over a Human Chorionic Gonadotropin (hCG) trigger shot, cases of OHSS have steadily decreased over the past several years. Both trigger shots assist in egg maturation, but Lupron has been shown to dramatically decrease the risk of OHSS.

A Lupron trigger shot cannot be used if a couple is planning intrauterine insemination (IUI). It can only be utilized with in vitro fertilization (IVF).

Again, when hCG is administered, there is an increased risk of OHSS. The two forms of OHSS, which can range from mild to severe, are:

  • Early-onset OHSS, which typically presents three to seven days after an hCG trigger shot and conveys an increased risk of preclinical miscarriage.
  • Late-onset OHSS, which is associated with pregnancy and presents 12 to 17 days after an hCG trigger shot. Late-onset OHSS tends to be more severe, but the risk of miscarriage is relatively low.


There are risk factors

You may be at higher risk for OHSS if you:

  • Are young
  • Have irregular menstrual cycles
  • Have polycystic ovary syndrome
  • Have a higher AMH level (anti-müllerian hormone)
  • Have a higher number of antral (egg-containing) follicles
  • Have a history of OHSS
  • Used an hCG trigger shot as part of your fertility treatment
  • Needed to increase the total dose of injectable medication
  • Have an aggressive response to medications


But there are also prevention strategies

Aside from a Lupron trigger shot, other OHSS prevention strategies include:

  • Deferring an embryo transfer
  • Undergoing a short course of cabergoline, which modulates hormone levels
  • Discontinuing injectable medications or canceling the current treatment cycle

It’s important that you contact your provider right away if you experience any of the symptoms mentioned, but rest assured that your specialist is working diligently to keep you healthy and prevent complications.

More resources

About the Author

Dr. Meghan Oakes is a reproductive health physician who specializes in helping couples with fertility issues.

You can visit Dr. Oakes at Methodist Reproductive Health Specialists on the campus of Methodist Women's Hospital.

See more articles from Meghan Oakes, MD
Photo of Meghan Oakes, MD