OHSS is a medical condition that can occur in women undergoing fertility treatments, particularly those involving assisted reproductive technologies like in-vitro fertilisation (IVF). It is characterised by an excessive response of the ovaries to hormonal stimulation, leading to swelling and fluid leakage into the abdomen and, in severe cases, the chest cavity. Understanding the causes, risk factors, symptoms, classification, prevention, and treatment options for OHSS is crucial for managing and mitigating this condition effectively.

What is Ovarian Hyperstimulation Syndrome (OHSS)?

Ovarian Hyperstimulation Syndrome (OHSS) is a complication that can occur during fertility treatments, particularly in-vitro fertilisation (IVF). It happens when the ovaries overreact to fertility medications used to stimulate egg production.

In a natural cycle, a woman typically releases one mature egg. In IVF, higher doses of fertility hormones are used to stimulate the ovaries to produce multiple eggs, increasing the chances of success. However, in some women, the ovaries become overly sensitive to these medications—especially the hormone human chorionic gonadotropin (hCG), which is given to trigger the final maturation of eggs before collection.

When OHSS occurs, the ovaries can swell and leak fluid into the abdominal and chest cavities. This leads to symptoms such as bloating, abdominal discomfort, nausea, and, in more severe cases, dehydration, electrolyte imbalances, and difficulty breathing.

OHSS is more common in IVF than in artificial insemination (AI) because AI typically uses lower hormone doses. Most cases of OHSS are mild and resolve on their own, especially once the woman’s period starts and hormone levels drop. However, close medical monitoring with ultrasound and hormone level tests (like estradiol) is essential to catch early signs and prevent complications.

Causes of OHSS

OHSS primarily arises from the administration of exogenous hormones during fertility treatments aimed at stimulating the ovaries to produce multiple eggs. The key hormones involved include:

• Gonadotropins: These are follicle-stimulating hormones (FSH) used to encourage the development of multiple ovarian follicles.
• Human Chorionic Gonadotropin (hCG): Administered to trigger the final maturation and release of eggs, hCG plays a pivotal role in the onset of OHSS. It induces the release of vasoactive substances, notably vascular endothelial growth factor (VEGF), which increases capillary permeability. This heightened permeability allows fluid to shift from blood vessels into the abdominal and, in severe cases, thoracic cavities, leading to the hallmark symptoms of OHSS.

Risk Factors for OHSS

• Polycystic Ovary Syndrome (PCOS): Women with PCOS have a higher sensitivity to gonadotropins, increasing their risk.
• Age: Younger women, particularly those under 35, are more susceptible.
• Low Body Weight: A lower body mass index (BMI) has been associated with an increased risk.
• High Estrogen Levels: Elevated estradiol levels during stimulation can indicate a heightened ovarian response, raising the risk.
• Previous Episodes of OHSS: A history of OHSS increases the likelihood of recurrence.
• Large Number of Developing Follicles: An excessive number of ovarian follicles can predispose to OHSS.

Symptoms of OHSS

The severity of OHSS symptoms can vary and are typically categorized as follows:

• Mild to Moderate OHSS:
  • Abdominal bloating or increased waist size o Mild to moderate abdominal pain
  • Nausea o Vomiting o Diarrhea
  • Tenderness in the area of the ovaries
• Severe OHSS:
  • Rapid weight gain, exceeding 2.2 kilograms (5 pounds) in 24 hours o Severe abdominal pain o Persistent nausea and vomiting
  • Decreased urination o Shortness of breath o Tight or enlarged abdomen o Dizziness

Classification of OHSS

OHSS is classified based on the severity and timing of symptom onset:

• Severity-Based Classification:
  • Mild OHSS: Characterised by ovarian enlargement and mild abdominal discomfort.
  • Moderate OHSS: Includes symptoms of mild OHSS plus ultrasound evidence of ascites (fluid in the abdomen).
  • Severe OHSS: Features large ovarian cysts, significant ascites, hemoconcentration, and potential respiratory distress.
• Timing-Based Classification:
  • Early OHSS: Develops within 3–7 days after hCG administration.
  • Late OHSS: Occurs more than 10 days after hCG administration, often associated with pregnancy-induced hCG production.

Complications of OHSS

While many cases of OHSS are mild and resolve spontaneously, severe cases can lead to serious complications:

• Ascites: Excessive fluid accumulation in the abdominal cavity.
• Pleural Effusion: Fluid buildup around the lungs, leading to breathing difficulties.
• Hemoconcentration: Increased blood viscosity, raising the risk of thrombosis.
• Electrolyte Imbalances: Resulting from fluid shifts and loss.
• Renal Failure: Due to reduced blood flow to the kidneys.
• Ovarian Torsion: Twisting of an enlarged ovary, potentially compromising its blood supply.

Risk Factors for Ovarian Hyperstimulation Syndrome (OHSS)

• Young age (under 30): Younger women tend to have more ovarian follicles and are more sensitive to fertility hormones, which makes them more likely to develop OHSS.
• Low body weight: Women with a low body mass index (BMI) or who are very thin may have a higher chance of developing OHSS, although not all studies agree on this link.
• Polycystic Ovary Syndrome (PCOS): Women with PCOS are at a higher risk because their ovaries often have many small follicles that can over-respond to hormone treatment.
• Previous pregnancy: Women who have been pregnant before seem to have a slightly higher risk of OHSS compared to those who have never been pregnant.
• Multiple pregnancy: If a woman becomes pregnant with twins or more during treatment, her body produces more hCG, which can make OHSS worse.

Treatment of Ovarian Hyperstimulation Syndrome (OHSS)

The treatment of OHSS depends on how severe the condition is. Some cases are mild and can be managed at home, while others may require hospital care.

Mild to Moderate OHSS:

• Drink plenty of fluids, especially those with electrolytes (like sports drinks).
• Rest with your legs raised to lower the risk of blood clots.
• Avoid alcohol and caffeine.
• Do not do intense physical activity to prevent ovarian twisting.
• Avoid sexual activity.
• Take pain relief medications if needed (as advised by your doctor).

Severe OHSS:

Giving fluids through an IV to prevent dehydration and maintain balance.

• Performing a paracentesis—a procedure to remove fluid from the abdomen if too much builds up.

Doctors will also carefully check the following to prevent complications:

• Liver function
• Blood clotting ability
• Electrolyte levels (fluid and salt balance)
• Kidney function
• Lung health 

Prevention of OHSS

• Individualised Gonadotropin Dosing: Tailoring hormone doses based on the patient’s risk factors to prevent excessive ovarian response.
• Use of GnRH Agonists: Employing GnRH agonists instead of hCG to trigger ovulation can reduce OHSS risk, though this may be associated with a lower pregnancy rate.
• Cycle Cancellation: In cases of excessive ovarian response, canceling the cycle before hCG administration can prevent OHSS. • Embryo Cryopreservation: Freezing

Conclusion:

Ovarian Hyperstimulation Syndrome (OHSS) is a significant complication associated with assisted reproductive technologies, notably in vitro fertilisation (IVF). While the majority of OHSS cases are mild and resolve without intervention, severe instances can lead to serious health concerns. Preventive measures, including careful patient selection, tailored ovarian stimulation protocols, and vigilant monitoring, are essential to minimize the risk of OHSS. In cases where OHSS develops, prompt recognition and appropriate management are crucial to ensure patient safety and improve outcomes.