What is Ovarian Hyperstimulation Syndrome (OHSS)? Causes, Symptoms & Treatment Explained

Ovarian hyperstimulation syndrome (OHSS) is a condition that can sometimes develop during fertility treatments, especially when hormonal medications are used to encourage the ovaries to produce multiple eggs.

In OHSS, the ovaries swell and become painful due to an exaggerated reaction to these hormones. This condition ranges from mild discomfort to more serious health problems that need medical care.

Although OHSS is less common today because of improved fertility treatment protocols, it remains an important concern for women undergoing assisted reproduction techniques like in vitro fertilization (IVF) or ovulation induction. Knowing the symptoms, causes, and prevention strategies can help women recognize and manage OHSS effectively.

Why Does OHSS Occur?

Typically, a woman releases one egg during each menstrual cycle. Fertility medications, especially injectable hormones, stimulate the ovaries to develop multiple eggs at once for procedures likeIVF. These drugs increase the number of follicles, fluid-filled sacs in the ovaries that hold eggs.

In some women, especially those with a high ovarian reserve or heightened hormone sensitivity, the ovaries respond too strongly. This leads to swelling and fluid leaking into the abdomen.

The hormone most often linked to OHSS is human chorionic gonadotropin (HCG). Fertility specialists give HCG as a "trigger shot" to help eggs mature before retrieval. However, HCG can make blood vessels near the ovaries more porous. It causes fluid to leak out and swelling to occur. If pregnancy happens in the same cycle, the body produces its own HCG, which can make OHSS symptoms worse.

Who Is More Likely to Develop OHSS?

Some women face a higher risk of OHSS. Those with polycystic ovary syndrome (PCOS) often have more follicles and hormone imbalances that increase this risk. Other factors that raise the chance of OHSS include:

• Being younger than 30 years old
• Having low body weight
• Experiencing very high estrogen levels during stimulation
• Developing many follicles during treatment
• Women who had OHSS before

Even women without these risks can develop OHSS, so it's important for everyone undergoing fertility treatments to be aware.

Symptoms of OHSS

OHSS symptoms usually start within a week after taking ovarian stimulation medications. If pregnancy occurs, symptoms might start later or last longer. The signs vary depending on severity:

Mild to Moderate OHSS Symptoms

• Feeling bloated and having abdominal swelling
• Mild to moderate lower belly pain
• Nausea
• Vomiting or diarrhea
• Tenderness in the lower abdomen
• Gaining a small amount of weight (more than 1 to 2 pounds per day)

Severe OHSS Symptoms

• Rapid weight gain (over 2.2 pounds or 1 kg within 24 hours)
• Intense abdominal pain
• Decreased urination
• Difficulty breathing or chest pain
• Tight or distended belly
• Blood clots, often in the legs or lungs
• Persistent nausea and vomiting

What Happens Inside the Body with OHSS?

The main problem in OHSS is that blood vessels become abnormally leaky. When hormones especially HCG, overstimulate the ovaries, the ovaries release substances that increase the permeability of nearby blood vessels. This causes fluid to move out of the blood vessels and accumulate in spaces like the abdomen or chest.

This fluid shift can lead to dehydration, low blood pressure, thicker blood (hemoconcentration), and imbalanced electrolytes. In serious cases, kidney function can suffer, and blood clots may form. Early detection and treatment are critical to avoid complications.

How Do Doctors Detect OHSS?

Doctors diagnose OHSS by combining physical symptoms with tests and imaging. The evaluation usually includes:

• Physical exam: Checking for swollen or tender abdomen and monitoring weight changes
• Blood tests: Measuring hormone levels, kidney function, and electrolyte balance
• Ultrasound: Using transvaginal scans to check ovary size and look for fluid buildup in the abdomen
• Chest X-ray: Rarely, to check for fluid in the lungs if symptoms suggest it

Doctors generally avoid pelvic exams in severe OHSS cases because they might cause ovarian rupture.

Treatment Options for OHSS

Treatment depends on how severe the condition is. The goals are to ease symptoms, correct fluid imbalances, and prevent serious complications.

For Mild to Moderate OHSS

• Drink plenty of fluids, especially those with electrolytes
• Avoid heavy exercise or strenuous activity
• Weigh yourself daily and measure your waist size to monitor swelling
• Rest and take acetaminophen to relieve pain if needed
• Keep in regular contact with your doctor

For Severe OHSS

• Hospital stay for close monitoring
• IV fluids to restore hydration and balance electrolytes
• Blood thinners to reduce the risk of clots
• Paracentesis (draining fluid from the abdomen) to relieve pressure
• Medications to decrease ovarian activity

Most mild or moderate OHSS cases resolve on their own within two weeks. When pregnancy occurs, symptoms can last longer because the body continues to produce HCG.

Can Women Have Healthy Pregnancies After OHSS?

Yes, healthy pregnancy is possible. OHSS usually does not affect the health of the pregnancy. With proper care and monitoring, most women recover fully and have normal pregnancies and deliveries. Doctors may keep a closer watch for a few weeks to prevent any complications.

How to Prevent OHS?

Modern fertility clinics use several strategies to lower the risk of OHSS:

• Starting with low doses of stimulation medications and adjusting carefully
• Monitoring hormone levels and ovarian response through frequent blood tests and ultrasounds
• Temporarily stopping hormone injections if estrogen levels get too high before the trigger shot ("coasting")
• Using GnRH agonists instead of HCG to trigger ovulation, reducing risk
• Freezing embryos in high-risk cases and delaying embryo transfer until hormone levels normalize
• Adding medications (especially in women with PCOS) to reduce OHSS risk
• Using a “freeze-all” approach to avoid fresh embryo transfer in risky cycles

These steps are personalized based on each patient’s risk factors and help keep OHSS rates low.

Diet and Lifestyle Tips During OHSS

No specific diet prevents OHSS, but good hydration and balanced nutrition support recovery. Eating small, protein-rich meals with electrolytes helps. Include foods such as:

• Lean proteins like chicken, tofu, or lentils
• Potassium-rich fruits like bananas and oranges
• Coconut water for electrolytes
• Whole grains and complex carbohydrates

Avoid intense workouts or heavy physical activity during and after treatment to reduce ovarian stress.

How Long Does OHSS Last?

Mild OHSS symptoms usually improve within 7 to 10 days. Severe cases may take longer, especially if pregnancy occurs, as the body continues producing HCG. With medical care, even serious OHSS typically resolves without lasting health problems.

Frequently Asked Questions (FAQs)

When is the highest risk of OHSS?
The risk of OHSS typically peaks around five to ten days after egg retrieval. During this time, the hormones that were used to stimulate your ovaries to produce multiple eggs are still in your system, and your ovaries may continue to produce hormones even after the eggs have been retrieved.

How many eggs cause OHSS?
Some women still develop an excess number of follicles or eggs and are therefore at risk of OHSS. If you have 20 or more follicles on ultrasound, or 20 or more eggs collected at the time of Egg Collection (Ovum Pick-up, OPU), you are at an increased risk of developing OHSS.

Why salt after egg retrieval?
Focusing on including more sodium rich foods is often recommended post retrieval. A way to minimize the effects of OHSS involves consuming sodium rich foods for a few days post retrieval to help draw the extra fluid out of your ovaries.

How many follicles indicate OHSS?
The presence of more than 15 follicles ≥10 mm on the day of triggering final oocyte maturation represents the best predictor of severe OHSS in IVF cycles.

Conclusion

Ovarian hyperstimulation syndrome is a possible side effect of fertility treatments, especially those that use hormone injections to stimulate egg production. While it can cause discomfort and, in rare cases, serious complications, most cases are mild and resolve naturally. Advances in fertility medicine have significantly reduced OHSS incidence.

If you undergo fertility treatments and experience symptoms like rapid weight gain, abdominal bloating, or pain, don’t ignore them. Contact your healthcare provider immediately. With careful monitoring and timely treatment, OHSS can be managed safely, allowing you to focus on your journey to pregnancy with confidence.