OHSS: Symptoms, Risk Factors and Treatment

The honest picture, with numbers

Ovarian hyperstimulation syndrome is what happens when the ovaries respond too strongly to the gonadotrophin drugs used to grow multiple follicles. RCOG describes the mechanism: overstimulated ovaries enlarge and release chemicals into the bloodstream, fluid leaks out of the blood vessels into the abdomen and, in severe cases, into the space around the heart and lungs, and OHSS can affect the kidneys, liver and lungs.

The frequencies matter, because the word "syndrome" makes everything sound catastrophic and most cases are not. RCOG states that mild OHSS is common in women having IVF, affecting as many as 33 in 100, while just over 1 in 100 will develop moderate or severe OHSS. The HFEA gives the same picture: around a third of women have mild OHSS, which can normally be treated effectively at home with pain relief, and fewer develop moderate or severe disease — but in very rare cases severe OHSS can be life-threatening, and RCOG notes that a very small number of deaths from OHSS have been reported.

Timing is predictable enough to plan around. The HFEA says patients who develop strong symptoms generally do so in the week after egg collection, and RCOG says most symptoms should resolve in 7 to 10 days.

The three severity bands

RCOG sets them out explicitly, and knowing which band you are describing makes the phone call to the clinic far more useful.

• Mild: mild abdominal swelling, discomfort and nausea.
• Moderate: the symptoms of mild OHSS, but the swelling is worse because fluid is building up in the abdomen, which can cause abdominal pain and vomiting.
• Severe: the symptoms of moderate OHSS with extreme thirst and dehydration. You may pass only small amounts of dark urine, and you may have difficulty breathing because of fluid building up in your chest. A serious but rare complication is a blood clot in the legs or lungs, which presents as a swollen tender leg, or chest pain and breathlessness.

The single most useful discriminator is not any one symptom but the direction of travel. Ordinary post-collection discomfort plateaus and then improves. OHSS escalates.

Who is at higher risk

RCOG lists the factors that raise the risk: having polycystic ovaries, being under 30 years old, having had OHSS previously, and becoming pregnant in the same IVF cycle in which symptoms appear, particularly with a multiple pregnancy. Pregnancy is on that list because the hormonal signal that drives the syndrome continues rather than switching off.

RCOG also notes that if treatment does not result in pregnancy, OHSS usually gets better by the time your next period starts, whereas if you do conceive it can worsen and last a few weeks or longer.

Prevention, and what clinics are required to do

NG257 recommendation 1.46.1 requires clinics providing ovarian stimulation with gonadotrophins to have protocols in place for preventing, diagnosing and managing OHSS, and the guideline points to the ESHRE guideline on ovarian stimulation for IVF and ICSI for the detailed prevention recommendations.

One preventive strategy has a clear regulator rating. The HFEA rates elective freeze-all cycles — creating embryos and freezing them all rather than transferring in the fresh cycle — green for reducing the risk of OHSS both in most fertility patients and in those at increased risk of it. Its rating for improving the chance of a baby is amber, so freeze-all is best understood as a safety measure with an uncertain effect on success, not the other way round.

What to do if you have mild symptoms

RCOG's home advice is specific and includes one instruction people get wrong. Drink fluids at regular intervals, according to how thirsty you feel. For pain, take paracetamol or codeine, no more than the maximum dose. Avoid anti-inflammatory drugs — aspirin, or aspirin-like drugs such as ibuprofen — because they can affect your kidneys. And remain active rather than lying still, to reduce the risk of a clot.

RCOG also advises avoiding sex and strenuous exercise while your ovaries are enlarged and painful, to avoid injuring them.

What happens at hospital

RCOG describes the assessment: questions about how much urine you are passing and whether it is darker than normal, blood pressure, pulse and breathing rate, an initial waist measurement and weight so that fluid build-up can be tracked, an ultrasound scan to measure the ovaries and check for fluid in the abdomen, and blood tests to see how concentrated your blood is and how well your kidneys are working.

Admission is likely if pain is not controlled by painkillers, if nausea and vomiting are severe, if the condition is not improving, or if you cannot easily get back for monitoring. Treatment does not reverse OHSS — it manages symptoms and prevents complications: pain relief, anti-sickness medication, an intravenous drip to replace fluids, and support stockings with heparin injections to prevent clots. RCOG notes heparin should continue for 7 days from resolution of symptoms if you are not pregnant, or until the end of the 12th week of pregnancy if you are. If the abdomen is tense with fluid, a paracentesis may be offered, in which a needle or tube is passed into the abdomen under ultrasound guidance to drain it, which relieves discomfort and improves kidney function and breathing.

What to do next

1. Ask your clinic before stimulation starts what your OHSS risk is and what its protocol is, as NG257 requires it to have one.
2. Ask whether freeze-all is appropriate for you if you are at higher risk. The HFEA rates it green for reducing OHSS.
3. Get the 24-hour number in writing. RCOG says clinics should provide full written information about OHSS and a 24-hour help number.
4. Weigh yourself daily after egg collection and note your waist measurement, so you can report a trend rather than a feeling.
5. Keep paracetamol in the house and put the ibuprofen away.
6. If admitted to a hospital other than your fertility unit, ask that your care is coordinated with a specialist in OHSS, as RCOG advises.

When to seek help

RCOG says to call for medical help if you develop any symptoms of OHSS, particularly if pain is not improving, or if you start to vomit, have urinary problems, chest pain or difficulty breathing. If you cannot reach your fertility clinic, contact your local A and E department, your general practice, or NHS 111.

The NHS advises calling 999 or going to A and E for difficulty breathing, pain in the chest or upper back, extreme thirst with much reduced urination, swelling anywhere on the body, low one-sided tummy pain, or pain at the tip of the shoulder. Do not drive yourself. If you have had OHSS and become pregnant, RCOG advises continuing support stockings and heparin until 12 weeks, and notes a raised risk of pre-eclampsia and preterm birth, with no known risk to the baby's development from the OHSS itself.