Ovarian Hyperstimulation Syndrome (OHSS)
An exaggerated ovarian response to fertility treatment
Quick Facts
- Type: Reproductive / fertility-treatment condition
- Cause: Strong response to ovary-stimulating medicines
- Common with: IVF and other assisted reproduction
- Seek urgent care: Severe pain, breathlessness, rapid weight gain
Overview
Ovarian hyperstimulation syndrome (OHSS) is a complication of fertility treatment in which the ovaries respond too strongly to the medicines used to stimulate egg production. The ovaries become enlarged and swollen, and fluid can shift out of the blood vessels into the abdomen and, in severe cases, around the lungs.
OHSS most often occurs after the use of injectable hormones in assisted reproduction such as in vitro fertilization (IVF), particularly around the time of egg retrieval or after a trigger injection. Most cases are mild and settle on their own, but a small number become severe and require hospital care. Fertility clinics monitor closely to reduce the risk and to catch the condition early.
Symptoms
Symptoms usually begin within a week or so of the trigger injection or egg retrieval and range from mild to severe.
- Mild: Bloating, mild abdominal discomfort, nausea, and slight weight gain.
- Moderate: Increasing abdominal swelling, more pain, vomiting, and noticeable weight gain.
- Severe: Rapid weight gain, severe abdominal pain and swelling, marked reduction in urination, shortness of breath, and persistent vomiting.
Severe symptoms, especially breathlessness, severe pain, or a sharp drop in how much you are passing urine, are warning signs that need urgent medical assessment.
Causes
OHSS is driven by the fertility medicines that stimulate the ovaries and the trigger injection that prompts the eggs to mature.
- Ovary-stimulating hormones: Injectable medicines encourage multiple follicles to grow at once.
- The trigger injection (hCG): The hormone used to mature the eggs is a key trigger for OHSS, prompting the ovaries to release substances that make blood vessels leaky.
- Pregnancy hormone: If pregnancy occurs in the same cycle, the body's own hCG can prolong or worsen the condition.
The leaking of fluid from blood vessels into the abdomen is what causes the swelling, weight gain, and, in severe cases, thickening of the blood and clotting risk.
Risk Factors
- Polycystic ovary syndrome (PCOS)
- Younger age and lower body weight
- A high number of follicles or very high hormone levels during stimulation
- A previous episode of OHSS
- Pregnancy occurring in the treatment cycle
Diagnosis
Diagnosis is based on the timing after fertility treatment along with symptoms and tests.
- Pelvic ultrasound: Shows enlarged ovaries and any free fluid in the abdomen.
- Blood tests: Check how concentrated the blood has become, kidney function, and salt balance.
- Symptom and weight monitoring: Tracking abdominal girth, weight, and urine output helps grade the severity.
Treatment
Treatment depends on severity. Mild cases are managed at home, while severe cases may need hospital care.
- Mild cases: Rest, drinking fluids to thirst, over-the-counter pain relief as advised, and monitoring for worsening symptoms.
- Moderate cases: Closer monitoring and sometimes medicines to ease symptoms.
- Severe cases: Hospital admission for intravenous fluids, drainage of excess abdominal fluid if it causes pain or breathlessness, and treatment to lower the increased risk of blood clots.
OHSS usually resolves over one to two weeks, or longer if pregnancy occurs. Clinics also use prevention strategies during treatment to lower the chance of it happening.
Prevention
- Careful dosing of stimulation medicines based on individual response
- Close monitoring with ultrasound and hormone levels during treatment
- Using an alternative trigger medicine in people at higher risk
- Freezing all embryos and delaying transfer in high-risk cycles
- Following clinic instructions about fluids, activity, and reporting symptoms
When to See a Doctor
Contact your fertility clinic if you develop bloating, abdominal pain, or nausea after fertility treatment. Seek urgent or emergency care for severe symptoms:
- Severe or worsening abdominal pain or swelling
- Shortness of breath or difficulty breathing
- Rapid weight gain over a few days
- Passing very little urine
- Calf swelling or pain, which could signal a blood clot
These signs can indicate severe OHSS or a complication and should not be ignored.
Frequently Asked Questions
What is ovarian hyperstimulation syndrome?
OHSS is a complication of fertility treatment in which the ovaries overrespond to stimulating medicines, becoming swollen and leaking fluid into the abdomen. It causes bloating, pain, and weight gain, and ranges from mild to, rarely, severe and serious.
When does OHSS usually happen?
It typically develops within about a week of the trigger injection or egg retrieval during fertility treatment such as IVF. If pregnancy occurs in the same cycle, the body's own pregnancy hormone can prolong or worsen the condition.
Is OHSS dangerous?
Most cases are mild and settle on their own within one to two weeks. A small number become severe, causing significant fluid buildup, breathing difficulty, kidney strain, and a higher risk of blood clots, which require hospital treatment.
When is OHSS an emergency?
Seek urgent care for severe abdominal pain or swelling, shortness of breath, rapid weight gain over a few days, passing very little urine, or calf pain and swelling. These can indicate severe OHSS or a blood clot.
Can OHSS be prevented?
Fertility clinics reduce the risk with careful medication dosing, close monitoring, using alternative trigger medicines for higher-risk people, and sometimes freezing all embryos to delay transfer. Following clinic advice about symptoms and fluids also helps.
References
- Mayo Clinic. Ovarian hyperstimulation syndrome (OHSS).
- American Society for Reproductive Medicine (ASRM). Ovarian hyperstimulation syndrome.
- MedlinePlus, U.S. National Library of Medicine. Infertility.