Ovarian hyperstimulation syndrome

Last revised by Joshua Yap on 6 Jan 2023

Ovarian hyperstimulation syndrome (OHSS) is a complication of controlled ovarian stimulation, which is an assisted reproduction technique used for in vitro fertilisation (IVF). Rarely, it may also occur spontaneously in pregnancy (see below). It consists of ovarian enlargement with an extravascular accumulation of fluid leading to variable weight gain, ascitespleural effusion, intravascular volume depletion, and oliguria.

The syndrome is relatively common, occurring in ~5% of patients undergoing in vitro fertilisation (IVF). There is probably an even higher incidence of the syndrome in "egg donors" due to their young age (which is a known risk factor for the disease), however, there is a known problem of lack of reporting of such cases.

  • high baseline ovarian volume 8

  • background polycystic ovaries 9

  • low body weight 8

  • long ovulation induction cycle duration 8

The clinical picture may vary from abdominal distension and discomfort to potentially life-threatening capillary leak with fluid sequestration in a third space, and massive ovarian enlargement. Pain, abdominal distention, nausea, and vomiting are frequently seen as symptoms 18.

Controlled ovarian stimulation is an assisted reproductive technique used to increase oocyte (egg) retrieval success and can cause ovarian hyperstimulation syndrome 18.

This syndrome is characterized by massive cystic ovarian enlargement and fluid shift from the intravascular compartment into the peritoneal, pleural or pericardial spaces. The vascular fluid leakage is thought to result from increased capillary permeability of mesothelial surfaces under the action of one or several vasoactive ovarian factors produced by multiple corpora lutea. Acute pelvic pain may result from stretching of the ovarian capsule or hemorrhage/rupture of a follicle.

Spontaneous ovarian hyperstimulation syndrome is a rare subtype and occurs in the absence of any external stimulation. This form can occur in pregnancy 15, or due to a genetic component. These have an association with early pubertal development and primary hypothyroidism (Van Wyk-Grumbach syndrome).

Ovarian stimulation in the hypothyroid child may result in estrogen production, breast development, endometrial proliferation, and vaginal bleeding. It is likely that raised TSH concentrations bind and stimulate the FSH receptor, although a similar overlap phenomenon might occur at the level of the pituitary, with enhanced TRH production stimulating the GnRH receptor with subsequent ovarian enlargement. The cystic ovarian enlargement resolves with thyroid hormone replacement. A hyperstimulation phenomenon in patients with an abnormal FSH receptor has been described.

The modified Golan classification subdivides ovarian hyperstimulation syndrome based on the clinical presentation and imaging findings 12,17.

  • serum estradiol (E2) levels are elevated 18

Imaging findings tend to be similar on ultrasound, CT and MRI.

The syndrome is usually self-limiting in most cases and management is mainly supportive, however, cases with fatal outcomes have been reported 14. Severe cases usually require hospitalization and close monitoring of hematocrit, liver function, renal function, serum electrolytes and oxygen saturation.

The profoundly altered maternal environment of ovarian hyperstimulation syndrome is a significant risk factor for miscarriage, especially when occurring in the early phase after IVF (defined as <10 days after oocyte retrieval) 16.

For ultrasound appearances in mild cases consider

Familiarity with ovarian hyperstimulation syndrome and the appropriate clinical setting should help avoid the incorrect diagnosis of an ovarian cystic neoplasm. When encountering severe forms not suspected by the clinician suggesting the diagnosis may reduce both morbidity and mortality.

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Cases and figures

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  • Case 4: grade 5
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  • Case 9: with ovarian torsion
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  • Case 10
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  • Case 10
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