OHSS in IVF: Symptoms, Causes, Risk Factors, Prevention and Treatment

What Is OHSS in IVF?

Ovarian hyperstimulation syndrome (OHSS) refers to a condition where the ovaries become swollen and tender due to an increased reaction to fertility medicines. In a regular menstrual cycle, one ovary releases a single egg. The process of stimulation for IVF involves the injection of hormones to cause multiple eggs to be produced by the ovaries. This may also lead to the ovaries producing certain chemicals that cause fluid to leak into the abdominal area, and may result in bloating and discomfort. According to a 2024 study published in the Journal of Personalized Medicine, OHSS is one of the most frequent complications, accounting for 30% of IVF cycles.

What Causes OHSS During IVF?

OHSS is caused by the same fertility medicines that help your ovaries produce multiple eggs, particularly the injection used to trigger final egg maturation. Two parts of the process matter most:

How Fertility Medicines Can Lead to OHSS

Gonadotrophins, injectable hormones such as FSH (a hormone that stimulates egg growth), help many eggs develop at once during stimulation instead of just one. When the ovaries overrespond, they produce many follicles (fluid-filled sacs, each holding a developing egg) and raise blood oestrogen, making them more likely to release the chemicals behind OHSS.

The Role of hCG in OHSS

Human chorionic gonadotropin (hCG) is the 'trigger injection' that helps eggs finish maturing roughly 36 hours before retrieval. Since it resembles a pregnancy hormone, hCG prolongs and intensifies the ovaries' response, which is why it is closely linked to OHSS. Doctors sometimes use an alternative trigger in higher-risk women.

Symptoms of OHSS

Signs and symptoms of ovarian hyperstimulation syndrome usually appear within a week or two of the trigger injection and range from mild to severe.

Mild Symptoms of OHSS

Mild OHSS is the most common form. You may notice abdominal bloating, mild pelvic discomfort, nausea, and fullness in the lower abdomen. These symptoms usually settle on their own within a week.

Moderate to Severe Symptoms of OHSS

Moderate OHSS adds vomiting, diarrhoea and rapid weight gain from fluid retention. Severe OHSS includes gaining more than a kilogram in a single day, severe abdominal pain, persistent vomiting, breathlessness, a tight, swollen abdomen and passing very little urine. These are signs that the fluid shift needs medical review.

When Should You Contact Your Fertility Specialist?

Call your clinic for rapid weight gain, severe abdominal pain, breathlessness, or noticeably less urine, so your doctor can check your hydration and kidneys before symptoms progress.

Risk Factors for OHSS

Certain factors make some women more likely to develop OHSS, which is why your fertility team assesses your risk before stimulation begins.

Previous History of OHSS

Having had OHSS in an earlier IVF cycle makes it more likely to happen again, so your doctor may adjust your protocol.

Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a hormonal condition in which the ovaries contain many small, immature follicles. These ovaries tend to respond more strongly to stimulation medicines, which raises OHSS risk.

High Ovarian Response During IVF

Women with high anti-Müllerian hormone (AMH, a blood marker of egg supply) who produce many follicles during stimulation are called high responders. This is one of the strongest predictors of who is at risk of OHSS during IVF.

Other Factors That May Increase OHSS Risk

A few other factors can also raise OHSS risk:

• Being under 35 years of age
• Having a lower body weight
• Becoming pregnant in the same cycle, since pregnancy produces more hCG
• Using hCG, rather than an alternative medicine, as the trigger injection

How Is OHSS Diagnosed?

OHSS is diagnosed through your symptoms, a physical exam, and tests checking how much fluid has shifted into your abdomen.

Medical History and Physical Examination

Your doctor will ask about your symptoms and how many days have passed since your trigger injection, then examine your abdomen for tenderness and swelling.

Ultrasound and Blood Tests

An ultrasound shows the size of your ovaries and any fluid collecting in your abdomen. Blood tests check your haematocrit (the concentration of red blood cells, which rises when fluid leaks from blood vessels), kidney function and electrolytes, helping your doctor grade OHSS severity.

Types and Severity of OHSS

Doctors classify OHSS into four severity levels:

Mild OHSS

Mild OHSS brings abdominal bloating, mild discomfort, and slightly enlarged ovaries, with no significant change on blood tests.

Moderate OHSS

Moderate OHSS adds nausea, vomiting and visible abdominal fluid on ultrasound, with more enlarged ovaries.

Severe OHSS

Severe OHSS brings a tense, fluid-filled abdomen, breathlessness, a marked rise in haematocrit, and reduced urine output, usually needing hospital monitoring.

Critical OHSS

Critical OHSS is rare, involving blood clots, significant kidney impairment or fluid around the lungs, and needs intensive hospital care.

Can OHSS Affect Fertility or IVF Success?

OHSS itself does not damage your ovaries or reduce your long-term fertility. If you develop moderate or severe OHSS, your fertility team may freeze your embryos and postpone the transfer to a later cycle, once your body has recovered.

Can OHSS Affect Pregnancy?

A common concern is whether OHSS can affect pregnancy after IVF once a cycle has triggered symptoms. As per the American Society for Reproductive Medicine, OHSS does not harm a developing pregnancy, though symptoms can last two to three weeks longer, since pregnancy produces more hCG.

How Can OHSS Be Prevented During IVF?

Knowing how to prevent OHSS during IVF starts with adjusting your protocol to your risk. Your fertility specialist has several tools:

Adjusting Fertility Medication Dosage

If you are a high responder, your doctor may prescribe a lower stimulation dose from the start, reducing the follicles that develop and lowering OHSS risk.

Monitoring Ovarian Response

Regular ultrasound scans and blood tests during stimulation let your doctor track your follicles and adjust medication if your ovaries respond faster than expected.

Trigger Injection and IVF Protocol Adjustments

In high-risk women, doctors often use a GnRH agonist (a medicine based on gonadotrophin-releasing hormone, which controls egg release) as the trigger instead of hCG, since it lowers OHSS risk considerably. A GnRH antagonist stimulation protocol, rather than a longer agonist one, also helps.

Embryo Freezing and Delayed Embryo Transfer

If OHSS risk is high after retrieval, your clinic may freeze all suitable embryos and delay transfer to a later cycle. This 'freeze-all' approach avoids the extra hCG an early pregnancy would add to an already overstimulated system.

How Long Does OHSS Last?

OHSS treatment and recovery time depend on how severe your symptoms are and whether pregnancy occurs in the same cycle. According to a 2018 study published in Journal of Ovarian Research, mild to moderate OHSS usually resolves within one to two weeks without pregnancy. Pregnancy in the same cycle can extend symptoms by several weeks, since it keeps producing hCG. Severe OHSS takes longer still, and your doctor will monitor you with blood tests until fluid balance and kidney function return to normal.

When Is OHSS Considered an Emergency?

OHSS is an emergency situation when it impacts the ability to breathe, circulation, or even the functioning of the kidneys. Seek medical attention immediately in case of severe breathlessness, chest pain, calf pain and swelling (possibly due to a blood clot), lack of urine, or abdominal pain despite painkillers.

Conclusion

For most women who get OHSS during the IVF process, it is a mild and transient experience that resolves itself before their pregnancy test is expected. There are many techniques to reduce the risk of this happening; the fertility specialists can either use less intense ovulation stimulation drugs, another trigger shot, or delay the embryo transfer process.
Understanding the symptoms and warning signs of OHSS and the associated risk factors gives both you and your physician the means of recognising early changes. It will not help with all of the uncertainties the IVF procedure holds, but at least it will give you an understanding of what your body is telling you.