OHSS (Ovarian Hyperstimulation Syndrome): Symptoms, Risk Factors and When to Seek Care

OHSS (ovarian hyperstimulation syndrome) is a condition that develops when the ovaries respond excessively to IVF medicines. Most of the time it is mild and limits itself. The information below offers a general framework and does not replace a diagnosis or treatment recommendation specific to the individual.

What is OHSS?

According to current patient information on this subject, OHSS is an excessive response that affects the whole body and arises with a wide range of clinical, ultrasound and laboratory findings. The ovaries enlarge, and fluid may collect in the abdominal cavity because of fluid leaking from the blood vessels.

Why does OHSS occur?

It is linked to an excessive response to the gonadotropins used to stimulate the ovaries and to the hCG that triggers maturation. In addition to IVF, it can be seen in assisted reproduction practices, including ovulation induction.

How is the severity of OHSS determined?

OHSS is classified as mild, moderate, severe or critical according to symptoms, ultrasound findings and laboratory results. The doctor determines which group you fall into and the way you will be monitored.

In whom is it seen more often?

According to current guidelines, risk factors include having had OHSS before, young age, low body mass index, polycystic ovary syndrome (PCOS), a high antral follicle count and a high AMH level. The development of many follicles during stimulation and the collection of many eggs are also linked to the risk. Current ovarian stimulation guidelines recommend that a risk assessment for a high response be made before stimulation is started. Having no risk factor does not mean that OHSS will not develop; the risk is specific to the person.

What are the symptoms, and when do they start?

Swelling and pain in the abdomen, nausea, vomiting, diarrhoea and weight gain are the symptoms reported. Signs of worsening include increasing abdominal pain, a decrease in the amount of urine, rapid weight gain, an increase in abdominal girth and shortness of breath.

When can OHSS appear in the early period of treatment?

It can appear in the days after the medicines that stimulate the ovaries, after the trigger and egg collection.

Can OHSS start or continue once a pregnancy occurs?

If a pregnancy occurs, the picture can start at a later stage or continue. For this reason symptoms are monitored after a positive pregnancy test too.

Is mild bloating usual during stimulation?

Because the ovaries enlarge with stimulation, mild swelling, a feeling of fullness in the abdomen and mild cramp are common, expected complaints.

How are diagnosis and monitoring done?

The diagnosis is made by assessing your symptoms, by imaging your ovaries and the fluid inside the abdomen on ultrasound, and by blood tests. Your doctor determines which tests will be done and how often, according to your situation.

Can OHSS be monitored at home, and when is hospital treatment considered?

According to current guidelines, in most cases OHSS limits itself, and people with a mild or moderate picture can be treated as outpatients. This decision belongs to your doctor. Admission to hospital is considered if your pain cannot be controlled, if you cannot come to regular check-ups, if you cannot take in enough fluid because of nausea, or if your symptoms worsen despite outpatient monitoring. Your doctor plans the details of treatment according to you.

Does OHSS increase the risk of clotting?

OHSS is linked to an increased risk of clot formation within the vessels (venous thrombosis).

How is the stimulation plan adjusted according to the risk of OHSS?

Your doctor chooses the strategies aimed at reducing the risk; none of them removes the risk completely. It is recommended that people at risk be identified before stimulation is started and that stimulation be adjusted to the person. According to current guidelines, when there is concern about OHSS the GnRH antagonist protocol can be preferred, and the gonadotropin dose is adjusted according to your ovarian reserve.

Why does the type of maturation trigger matter?

Current guidelines recommend, in those at risk of OHSS, the use of a GnRH agonist trigger instead of hCG for final maturation, together with freezing all embryos; the agonist trigger is regarded as the first choice in people at risk.

Why are freezing the embryos and postponing the transfer considered?

Freezing all embryos and leaving the transfer for later is not a routine approach applied in every cycle; it has a place in a high risk of OHSS. Current guidelines recommend this strategy in those at high risk of OHSS in order to minimise late OHSS. For early OHSS, a group of medicines called dopamine agonists is recommended; your doctor decides which medicine will be used, when and for how long.

How does moderate or severe OHSS affect pregnancy follow-up?

According to current guidelines, IVF pregnancies complicated by moderate or severe OHSS are linked to an increased risk of miscarriage, venous thrombosis, gestational diabetes, disorders linked to high blood pressure, placental abruption, preterm birth and low birth weight. This is an association and does not mean that these problems will be experienced in every pregnancy with OHSS. These pregnancies are regarded as high risk and are monitored closely.

How is the next treatment planned if you have had OHSS?

Having had OHSS before increases the risk of its recurring; but the next treatment can be adjusted according to you. You need to make the plan together with your doctor, who knows the details of the picture you had.