Ovarian Hyperstimulation Syndrome

What is ovarian hyperstimulation syndrome?

Ovarian hyperstimulation syndrome (often shortened to OHSS) is a complication of fertility treatment in which the ovaries respond too strongly to the hormone medications used to make them produce eggs. The ovaries swell, and fluid leaks out of the blood vessels into the abdomen (belly) and, in more serious cases, into the chest. This fluid shift can cause bloating, pain, dehydration, and, rarely, dangerous complications.

The condition almost always affects women who are going through ovarian stimulation, the part of in vitro fertilization (IVF) or other fertility treatments in which injectable hormones are used to encourage several eggs to mature at once. It can also occur, much less often, in women taking oral or injectable medications to induce ovulation without IVF. Spontaneous ovarian hyperstimulation syndrome without any fertility drugs is very rare.

Most cases are mild and settle on their own within one to two weeks. A smaller number are moderate or severe and need closer medical care. Because the condition is linked to a treatment cycle, it is usually recognized and managed by the fertility team that is caring for the patient. At Acibadem, this care sits within the IVF and reproductive health department.

Ovarian hyperstimulation syndrome symptoms

Ovarian hyperstimulation syndrome symptoms usually begin within a few days of the trigger injection (the hormone shot given to finish maturing the eggs before retrieval) or in the days after egg collection. Doctors often describe two patterns. Early-onset OHSS appears within about a week of the trigger and reflects the immediate effect of the medications. Late-onset OHSS appears later, typically once a pregnancy has started, because the pregnancy hormone hCG (human chorionic gonadotropin) keeps stimulating the already enlarged ovaries. Late-onset cases tend to last longer and are more likely to be severe.

Common symptoms in mild cases include:

• Mild to moderate bloating or a feeling of fullness in the abdomen
• Mild lower abdominal discomfort or aching
• Tenderness over the ovaries
• Mild nausea
• A small amount of weight gain

Symptoms that suggest moderate ovarian hyperstimulation syndrome include:

• Increasing abdominal swelling and a visibly larger waistline
• Persistent nausea and vomiting
• Reduced appetite
• Rapid weight gain over a few days
• Diarrhea

Severe OHSS may cause:

• Marked abdominal distension (a tight, swollen belly) that makes it hard to bend or lie flat
• Shortness of breath or difficulty breathing, which may mean fluid has collected around the lungs
• Passing very little urine, or dark urine, a sign of dehydration and reduced kidney blood flow
• Severe or worsening abdominal pain
• Dizziness, faintness, or a racing heartbeat
• Calf pain, leg swelling, or chest pain, which can signal a blood clot

Because the fluid that leaks from the blood vessels comes from the bloodstream, the blood itself becomes more concentrated. This is why dehydration and clotting problems can develop even though the body appears to be holding onto fluid. The severity of symptoms does not always match how enlarged the ovaries look, so any change in symptoms during a treatment cycle should be reported to the fertility team.

Causes and risk factors

The direct ovarian hyperstimulation syndrome causes are the hormone medications used during fertility treatment. Injectable gonadotropins (hormones that stimulate the ovaries to grow follicles, the small fluid-filled sacs that contain eggs) can lead to a large number of follicles developing at the same time. When hCG is then given as a trigger, or when a pregnancy begins to produce its own hCG, the stimulated ovaries release substances that make blood vessels leaky. One key substance is vascular endothelial growth factor (VEGF), a protein that increases the permeability of blood vessel walls. Fluid, protein, and salts shift out of the bloodstream and into the abdominal cavity.

Not every woman who receives these medications develops OHSS. Several factors are known to raise the risk:

• Polycystic ovary syndrome (PCOS): a hormonal condition in which the ovaries contain many small follicles and tend to respond very strongly to stimulation.
• Younger age: women under about 35 usually have a larger supply of eggs and respond more vigorously.
• Low body weight: a lower body mass index has been associated with a higher risk in some patients.
• A high number of follicles or eggs: when ultrasound shows many developing follicles, or when a large number of eggs is collected, the risk rises.
• High estradiol levels: estradiol is a form of estrogen produced by the growing follicles; very high blood levels during stimulation are a warning sign.
• Previous OHSS: having had the condition in an earlier cycle makes it more likely to happen again.
• hCG trigger and hCG support: using hCG to trigger ovulation, or to support the early luteal phase after egg collection, increases the risk compared with alternatives.
• Pregnancy in the same cycle: especially a pregnancy with more than one embryo, because the rising hCG prolongs and worsens the condition.

Fertility teams try to identify these risk factors before and during a cycle so that medication doses and the treatment plan can be adjusted. Even with careful planning, however, OHSS cannot always be predicted or fully prevented.

Diagnosis

Ovarian hyperstimulation syndrome diagnosis is based mainly on the patient’s history and symptoms in the context of recent fertility treatment, supported by a physical examination, ultrasound, and blood tests. There is no single test that confirms it; instead, doctors look at the overall picture and use clinical criteria to grade the condition as mild, moderate, severe, or critical.

The steps usually include:

• Medical history: the timing of symptoms in relation to the trigger injection, egg retrieval, or embryo transfer, and whether a pregnancy test is positive.
• Physical examination: checking the abdomen for swelling and tenderness, measuring weight and waist circumference, and checking blood pressure, heart rate, and breathing.
• Pelvic ultrasound: to measure the size of the ovaries and to look for free fluid in the abdomen (called ascites). Ultrasound of the chest may be used if breathing symptoms suggest fluid around the lungs.
• Blood tests: a complete blood count to check how concentrated the blood has become (hematocrit and hemoglobin), electrolytes such as sodium and potassium, kidney function tests (creatinine and urea), liver function tests, and sometimes clotting tests.
• Urine output monitoring: keeping track of how much urine is passed helps show whether the kidneys are receiving enough blood flow.
• Pregnancy test: because a positive test raises the chance that the condition will last longer or worsen.

Doctors also rule out other causes of abdominal pain after fertility treatment, such as an ovarian cyst that has twisted or ruptured, internal bleeding after egg collection, pelvic infection, appendicitis, or an ectopic pregnancy (a pregnancy growing outside the uterus). Grading the severity helps decide whether care can continue at home or whether admission to the hospital is needed.

Treatment options

There is no medication that reverses ovarian hyperstimulation syndrome directly. Ovarian hyperstimulation syndrome treatment is supportive, meaning it focuses on relieving symptoms, preventing complications, and giving the body time to recover while the hormone levels fall. The approach depends on how severe the condition is and whether a pregnancy is developing.

Mild cases: observation and self-care at home

Most women with mild OHSS are monitored as outpatients. Your doctor may advise:

• Drinking fluids regularly, guided by thirst, rather than restricting or forcing large volumes
• Taking simple pain relief such as acetaminophen (paracetamol); nonsteroidal anti-inflammatory drugs such as ibuprofen are often avoided because they can affect kidney function in this setting
• Avoiding strenuous exercise and sexual intercourse, which could injure or twist the enlarged ovaries
• Weighing yourself and measuring your waist daily, and noting how much urine you pass
• Staying gently active rather than lying in bed all day, to reduce the risk of blood clots

Regular check-ins with the fertility team, often every day or two by phone or in the clinic, allow early detection of any worsening.

Moderate to severe cases: hospital care

Women whose symptoms worsen, who cannot keep fluids down, who pass very little urine, or who show signs of fluid around the lungs are usually admitted to the hospital. Care there may include:

• Intravenous fluids: given through a vein to correct dehydration and support kidney function. In some cases doctors use albumin or similar solutions to help hold fluid within the blood vessels.
• Anti-nausea medication: to control vomiting so that fluids can be taken by mouth.
• Pain relief: adjusted to the level of discomfort while avoiding drugs that stress the kidneys.
• Blood clot prevention: injections of a blood-thinning medication (low-molecular-weight heparin) and compression stockings are commonly used, because the concentrated blood and reduced movement raise the risk of clots.
• Paracentesis: a procedure in which a thin needle is passed, under ultrasound guidance, into the abdomen (or sometimes through the vagina) to drain excess fluid. Removing fluid relieves pressure, eases breathing, and often improves kidney function. It can be repeated if fluid builds up again.
• Drainage of chest fluid: if fluid around the lungs causes breathing difficulty, it may be drained in a similar way.
• Close monitoring: daily blood tests, weight, waist measurement, fluid intake and urine output charts, and repeat ultrasound scans.

Adjusting the fertility cycle

When the risk of OHSS is recognized during stimulation, the team may change the plan to limit its severity. Options include lowering medication doses, using a different type of trigger injection (a GnRH agonist instead of hCG) in suitable protocols, avoiding hCG for luteal support, or freezing all embryos and postponing the transfer to a later cycle so that no pregnancy hormone adds to the stimulation. Once OHSS has developed, doctors may also use certain medications, such as dopamine agonists, that appear to reduce fluid leakage from blood vessels; these are used selectively and not in every case.

Critical cases and surgery

Rarely, OHSS becomes critical, with kidney failure, severe breathing problems, large blood clots, or a very tight abdomen. These patients are treated in an intensive care unit. Surgery is not a treatment for OHSS itself and is generally avoided, because the ovaries are fragile and bleed easily. It is reserved for complications such as ovarian torsion (twisting of the ovary, which cuts off its blood supply), a ruptured cyst with internal bleeding, or an ectopic pregnancy.

Living with ovarian hyperstimulation syndrome and outlook

For most women, OHSS is a temporary condition. Mild cases usually resolve within about a week or two as the hormone levels drop after the treatment cycle. If a pregnancy has not occurred, symptoms typically ease quickly once menstruation begins. If a pregnancy has occurred, symptoms may persist or worsen for several weeks, because hCG continues to rise until roughly the end of the first trimester, and recovery can take longer.

Having OHSS does not appear to harm the long-term function of the ovaries, and most women go on to have normal fertility afterward. There is no strong evidence that a pregnancy conceived in a cycle complicated by OHSS is at greater risk of birth defects. Some studies suggest a possible link with certain pregnancy complications, but the evidence is not consistent, and your obstetric team will monitor the pregnancy as they would any IVF pregnancy.

Serious complications, including blood clots, kidney injury, and fluid around the lungs, are uncommon but can be life-threatening if not treated promptly. This is why close monitoring and early reporting of symptoms matter. Deaths from OHSS are extremely rare in settings where fertility care is well supervised.

After recovery, it is reasonable to discuss with your fertility team how future cycles might be planned differently. A history of OHSS is one of the strongest predictors of it happening again, so doses, trigger type, and the timing of embryo transfer are often reviewed. Emotionally, OHSS can be distressing, especially when it delays an embryo transfer or complicates an eagerly awaited pregnancy. Support from a partner, counselor, or fertility nurse can help during this period.

Frequently asked questions

What are the first ovarian hyperstimulation syndrome symptoms to watch for?

The earliest signs are usually bloating, a sense of fullness or pressure in the lower abdomen, mild discomfort over the ovaries, and mild nausea, appearing within a few days of the trigger injection or egg collection. Some abdominal fullness is expected after stimulation, so mild symptoms do not necessarily mean OHSS. Symptoms that increase day by day, rather than improving, are what prompt doctors to look more closely.

What are the main ovarian hyperstimulation syndrome causes?

OHSS is caused by an exaggerated response of the ovaries to fertility hormones, particularly when hCG is given as a trigger or produced by an early pregnancy. The stimulated ovaries release substances that make blood vessels leaky, allowing fluid to shift into the abdomen. Women with polycystic ovary syndrome, a high number of follicles, very high estradiol levels, or a previous episode are at higher risk.

How is ovarian hyperstimulation syndrome diagnosis made?

Doctors diagnose OHSS from the combination of recent fertility treatment, typical symptoms, and findings on examination. Ultrasound shows enlarged ovaries and free fluid in the abdomen, and blood tests measure how concentrated the blood is and how well the kidneys are working. The condition is then graded from mild to critical, which guides treatment. Other causes of pain after egg collection are ruled out at the same time.

What does ovarian hyperstimulation syndrome treatment involve?

Treatment is supportive. Mild cases are managed at home with adequate fluids, simple pain relief, rest from strenuous activity, and regular check-ins. Moderate and severe cases may need hospital care with intravenous fluids, anti-nausea medication, blood-thinning injections to prevent clots, and drainage of abdominal fluid if the swelling is causing pain or breathing difficulty. Surgery is reserved for rare complications such as a twisted or bleeding ovary.

How long does ovarian hyperstimulation syndrome last?

In most cases, symptoms settle within one to two weeks as hormone levels fall. If you become pregnant in the same cycle, OHSS may last longer, sometimes several weeks, because pregnancy hormone continues to stimulate the ovaries. Your fertility team will usually continue monitoring until symptoms have clearly resolved.

Can ovarian hyperstimulation syndrome be prevented?

It cannot be prevented in every case, but the risk can often be reduced. Fertility specialists may use lower doses of stimulation medication in women at higher risk, choose a GnRH agonist trigger instead of hCG in suitable protocols, avoid hCG for luteal support, or freeze all embryos and postpone the transfer so that no pregnancy hormone adds to the stimulation.

Does ovarian hyperstimulation syndrome affect the chance of pregnancy or the baby?

OHSS itself does not appear to reduce the chance that an embryo will implant, and many pregnancies proceed normally after an episode. There is no clear evidence that it causes birth defects. When the risk of severe OHSS is high, doctors may recommend freezing embryos and transferring them later, which delays the attempt but is intended to protect the patient’s health.

When to see a doctor

If you are going through fertility treatment, report any new or worsening abdominal symptoms to your fertility team promptly, even if they seem minor. Seek urgent medical attention, or go to the nearest emergency department, if you experience any of the following red-flag signs:

• Severe or rapidly worsening abdominal pain or swelling
• Shortness of breath, difficulty breathing, or inability to lie flat
• Vomiting that prevents you from keeping fluids down
• Passing very little urine, or no urine for several hours, or very dark urine
• Rapid weight gain of more than about one kilogram (two pounds) in a day
• Dizziness, fainting, or a very fast heartbeat
• Pain, swelling, or redness in one leg, or sudden chest pain
• Confusion or unusual drowsiness

These signs may indicate severe OHSS, a blood clot, internal bleeding, or another complication that needs immediate assessment. Always tell emergency staff that you have recently had fertility treatment, as this changes how they investigate your symptoms.