Ovarian Hyperstimulation Syndrome (OHSS)

Overview

Ovarian hyperstimulation syndrome (OHSS) is a condition in which the ovaries overreact to the hormones used in fertility treatment, becoming swollen and enlarged. As part of this reaction, fluid can leak from blood vessels into the abdomen and other tissues.

OHSS most often occurs during fertility treatments that stimulate the ovaries to produce multiple eggs, such as in vitro fertilization (IVF). Most cases are mild and improve on their own, but a small number become moderate or severe, with significant fluid buildup and other complications that require medical care. Knowing the warning signs helps people getting fertility treatment seek help early.

OHSS is one of the more important risks of fertility treatment, and clinics watch carefully for it during ovarian stimulation. Most people who develop it have a mild form that improves on its own, but because a small number become seriously unwell, knowing the warning signs and staying in contact with the clinic is essential.

Symptoms

Symptoms usually begin within a week or so after the ovaries are stimulated or after egg collection.

• Bloating and abdominal swelling
• Mild to moderate pelvic or abdominal pain
• Nausea, vomiting, or diarrhea
• Tenderness in the ovary area
• Weight gain from fluid buildup

Severe warning signs include rapid weight gain, severe abdominal pain, persistent vomiting, much reduced urination, shortness of breath, and pain or swelling in the legs. These can signal severe OHSS or a blood clot and need urgent medical care; call your clinic or emergency services right away.

Causes

OHSS is caused by the ovaries responding too strongly to hormones used in fertility treatment, particularly the hormone hCG given as part of treatment, which can trigger the syndrome.

• Fertility medications: Injectable hormones that stimulate the ovaries to develop multiple follicles.
• hCG trigger: The hormone used to mature eggs can set off the fluid shifts seen in OHSS.
• Pregnancy: If pregnancy occurs in the same cycle, the body's own hCG can prolong or worsen symptoms.

The swollen ovaries release substances that make blood vessels leak fluid into the abdomen, which drives the symptoms.

Risk Factors

• Undergoing ovarian stimulation for IVF or other fertility treatment
• Polycystic ovary syndrome (PCOS)
• Younger age and lower body weight
• High numbers of developing follicles or high estrogen levels during treatment
• A previous episode of OHSS
• Becoming pregnant in the treatment cycle

Diagnosis

Doctors diagnose OHSS based on the timing, symptoms, and tests during fertility treatment:

• Symptom review: Bloating, pain, and other symptoms after ovarian stimulation.
• Physical examination: Checking for abdominal swelling and tenderness.
• Ultrasound: To see the enlarged ovaries and any fluid in the abdomen.
• Blood tests: To assess hydration, kidney function, blood concentration, and electrolytes in moderate or severe cases.

Treatment

Treatment depends on severity. Most cases are mild and managed at home.

• Mild cases: Rest, drinking fluids, monitoring weight and symptoms, and over-the-counter pain relief as advised by the clinic.
• Moderate cases: Closer monitoring, sometimes draining excess abdominal fluid to relieve discomfort.
• Severe cases: Hospital care with intravenous fluids, careful monitoring, fluid drainage, and treatment to prevent or manage blood clots.
• Adjusting treatment: The fertility team may modify or delay parts of the cycle to reduce risk.

Symptoms often improve within one to two weeks, though they may last longer if pregnancy occurs. Following the clinic's instructions closely is important.

Prevention

Fertility teams take steps to lower the risk of OHSS, especially in people known to be at higher risk:

• Using the lowest effective dose of stimulating medicines
• Careful monitoring of follicles and hormone levels during treatment
• Adjusting or changing the trigger medication when risk is high
• Sometimes freezing embryos and delaying transfer to a later cycle
• Promptly reporting symptoms so care can begin early

When to See a Doctor

Contact your fertility clinic if you develop bloating, pelvic pain, or nausea after treatment. Seek urgent or emergency care for severe warning signs, including:

• Rapid weight gain or severe, worsening abdominal pain
• Persistent vomiting or much reduced urination
• Shortness of breath
• Pain, swelling, or redness in a leg, which may signal a blood clot
• Fainting or feeling very unwell

Severe OHSS can become serious quickly, so do not wait to seek help.

Related Topics

Frequently Asked Questions

References

1. American Society for Reproductive Medicine (ASRM). Ovarian Hyperstimulation Syndrome.
2. Mayo Clinic. Ovarian hyperstimulation syndrome.
3. MedlinePlus, U.S. National Library of Medicine. In vitro fertilization (IVF).
4. National Health Service (NHS). Ovarian hyperstimulation syndrome (OHSS).