All you need to know about OHSS (Ovarian Hyperstimulation Syndrome) from IVF

What is OHSS?

OHSS stands for Ovarian Hyperstimulation Syndrome. It is a common side effect from stimulation medications often used in IVF and other assisted reproduction treatments. It occurs when your body has a greater than expected response to these stimulation medications and creates excessively large or too many follicles containing eggs.

The Science bit of OHSS


What causes OHSS

At the moment the complete cause of OHSS is not fully understood, however, the current research is as follows. OHSS is an iatrogenic (medically induced) complication of assisted reproduction techniques, specifically stimulation and hCG medications.

It’s attributed to cystic growth of the ovaries, with specific movement of fluid from intravascular to the third space (which is essentially a space where fluid shouldn’t be). This is caused by the creation of new capillaries in the ovaries known as ovarian neoangiogenesis and those capillaries becoming more permeable (easier to have liquids pass through).

Recent research has shown that it isn’t just the medications that cause it but the fact that the enlarged ovaries produce  vasoactive substances which include interleukins, tumour necrosis factor-α, endothelin-1, and vascular endothelial growth factor which all contribute to the increased permeability of the capillaries.

This leads to leaking of fluid from the follicles or from a rupture of the follicles and development of ascites which are fluid pockets of more than 25ml. Excessive levels of fluid build up can lead to oedema, hydrothorax (fluid in the chest cavity) and/or hydropericardium (fluid in the heart sac).For a more detailed overview check out the piece on National institute of health


How common is OHSS

The research into OHSS is getting more robust each year as it is a sometimes-serious side effect and one of the most common causes of a cancelled IVF cycle. For instance, we have a friend who had 32 follicles from her stimulation and had to have the fresh transfer cancelled meaning that she will have to have FET for the remaining embryos.

The most recent rates of OHSS are

Mild OHSS – 30% will experience mild OHSS symptoms

Moderate OHSS – 3-6% depending upon treatment protocol will experience moderate OHSS

Severe OHSS – 0.1-1% of women will experience severe OHSS dependent upon treatment protocol

So, there is a chance if you undergo IVF treatment then you may experience some form of OHSS but the moderate and severe versions are still rare.

Are there any risk factors which increase my chances of OHSS?

Your chances of getting OHSS are personal to you, your circumstances and how your body reacts to treatment. Although it is known that there are certain factors which lead to an increased risk of suffering with OHSS they are:

  • Your stimulation protocol – The more aggressive the stimulation the higher your chance of getting OHSS
  • Age – Younger people tend to react more strongly to stimulation medications and as such it increases the chance of OHSS
  • If you have had OHSS – Research show’s that if you have had OHSS before you are more likely to suffer with it again.
  • PCOS – Those who suffer with polycystic ovary syndrome have a higher chance of OHSS.
  • Women with a BMI under 19

What are the symptoms and clinical presentations of OHSS?

Ascites and bloating – Are caused by the leaking of the fluid into the third space. The build-up can cause ascites and you to feel bloated and visibly swollen around the abdomen

Localized or generalized peritonitis (infection of the tummy) – You can get an infection in the abdomen either in a specific place or more generally in the abdomen reason. The main reason for this is irritation of the abdominal cavity, this can be made worse through ruptured cysts and inflammation. This can cause pain and elevated temperature

Acute abdominal pain – This is mainly seen in moderate to severe OHSS and is usually due to a ruptured cyst, ovarian torsion (means twisting) or blood in the abdomen.

Low blood pressure and or low blood volume – Because the fluid is moving from the follicle and other fluid filled sacs to the third space it causes a loss of blood volume which also results in low blood pressure again this is only usually seen in severe cases of OHSS.

Trouble breathing – This only happens in severe OHSS because the ovaries and the fluid build up has become that severe that it stops your diaphragm (the muscle that creates space in your chest to allow the lungs to expand) from moving properly.

Increased blood clotting – This is probably due to the reduction in blood volume although it’s not clearly understood yet. But this can cause a DVT (deep vein thrombosis – blood clot in the legs) or a pulmonary embolus (blood clot in the lungs). This is only seen in severe cases.

Dehydration and imbalance of electrolytes – The fluid moving means that the salts and water are reabsorbed. This can lead to acidosis (acidity in the blood) if not monitored and fluids replaced.

Acute renal failure– In the most severe cases this imbalance and dehydration can cause the kidneys to fail.

How is the severity of OHSS decided?

OHSS is split into mild, moderate and severe with further subdivisions within mild and severe and they are as follows

Mild (grade 1) OHSS – Bloated and swollen abdomen with mild pain or discomfort

Mild (grade 2) OHSS – As above but are also nauseous or being sick, have diarrhoea and have ovarian swelling of between 5-12cm

Moderate (grade 3) OHSS – All the above plus an ultrasound shows evidence of ascites.

Severe (grade 4) OHSS – All the above plus clinical presentation of ascites and or trouble breathing

Severe (grade 5) OHSS – All of the above and reduction in blood volume and or increased blood viscosity.

Diagnosis and treatment of OHSS

If you develop OHSS it will depend upon the severity of the condition as to how it will be treated.

A diagnosis is made using a medical history including change in weight, a thorough examination, ultrasound and blood tests. These will allow the doctor to determine the severity of your OHSS and the best course of action

Treatment of mild to moderate OHSS is usually at home and includes:

  • Use of over the counter painkillers such as paracetamol or codeine – don’t use Ibuprofen
  • Drink fluids but not to excess to help keep your electrolytes balanced
  • Anti-nausea medications will be prescribed if necessary
  • Avoid sex or heavy physical activity as this could result in a rupture to an ovary
  • Monitor how frequently you are urinating
  • You should be checked by your doctor or clinic every 3 days.
  • Your clinic will determine if your cycle should be stopped, as if you do get pregnant OHSS can last the entire pregnancy.

Treatment of moderate to severe OHSS is as follows and is often performed in a hospital:

  • If you aren’t pregnant then your IVF cycle will likely be cancelled
  • Stronger painkillers may be used if required – especially if you develop ovarian torsion or a rupture
  • Administration of anti-nausea medications
  • IV fluid drip to help dehydration and electrolyte rebalancing
  • Catheterisation for continued urine output monitoring
  • Stockings to reduce the chance of a clot forming
  • Regular vital sign checks
  • Chest x-rays and ultrasounds
  • A low sodium diet
  • Possible draining of fluid from the abdomen through a needle.

In very severe cases you may have to go onto intensive care and or surgery to repair ruptures or support your vital organs although this is very rare.

What is the recovery from OHSS?

If the symptoms of OHSS are caught in time, then they can last anything from a few days to a few weeks if you’re not pregnant. If you do become pregnant then they can potentially last the entirety of your pregnancy.

More complex and severe cases of OHSS which require hospital admission are more likely to last a few weeks to a month. Also, if you have to have complex treatments including surgery of organ support then your recovery time can be much greater, around 3 months, however, please note again this incredibly rare.

Will getting Ovarian hyper stimulation Syndrome impact my IVF Cycle?

I know it’s not the answer you want but it does depend. Your doctor and clinic in consultation with yourself will come to this decision. If it is mild to moderate and understand that if you have a successful cycle you may suffer with OHSS throughout pregnancy and your doctor is happy that it’s safe then you will continue.

If you are higher in the moderate scale or severe it is likely that they will cancel your IVF cycle.

It’s important to note that unless you are immediately admitted into hospital for treatment your clinic may still go through egg collection and fertilisation then freeze the embryos. This means that you will be able to use any frozen embryos you may have produced as part of a frozen embryo transfer cycle (link to our article) in the future. So even if they do need to cancel the fresh embryo transfer that doesn’t mean all your hard work is wasted.

Will OHSS harm my baby if I get pregnant

At the current time there is absolutely no evidence that OHSS causes any harm to your baby if you have mild, moderate or severe that do not require any surgical or intensive care interventions. Unfortunately, if you do have to have lifesaving surgery or intensive care treatment because of organ failure then these symptoms and treatments could have an impact on your baby’s health. Although the doctors will have a detailed discussion with you and your next of kin if this is the case and this is incredibly rare!


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