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Prevention and management of ovarian hyperstimulation syndrome

Best Practice & Research Clinical Obstetrics & Gynaecology, 6, 26, pages 817 - 827

Ovarian hyperstimulation syndrome is a relatively common complication of ovarian stimulation and can be life-threatening. The pathophysiology of ovarian hyperstimulation syndrome is characterised by increased capillary permeability, leading to leakage of fluid from the vascular compartment, with third space fluid accumulation and intravascular dehydration. The combined use of a gonadotrophin-releasing hormone antagonist protocol with gonadotrophin-releasing hormone agonist triggering and oocyte and embryo freezing has considerable promise in preventing ovarian hyperstimulation syndrome. Women with severe ovarian hyperstimulation syndrome require hospitalisation for more careful monitoring and treatment. Transvaginal paracentesis can be used as an outpatient treatment to prevent the need for hospitalisation. The inhibition of vascular permeability seems to be a novel therapeutic approach to preventing and treating ovarian hyperstimulation syndrome.

Keywords: ovarian hyperstimulation syndrome, complications, prevention, management.


Ovarian hyperstimulation syndrome (OHSS) is a relatively common complication of ovarian stimulation and can be life-threatening. 1 It is characterised by enlargement of the ovaries, fluid retention, and weight gain. Ovarian hyperstimulation syndrome is self-limiting and will undergo gradual resolution with time. The pathophysiology of OHSS is characterised by increased capillary permeability, leading to leakage of fluid from the vascular compartment, with third-space fluid accumulation and intravascular dehydration. 2 Although the exact cause of OHSS has not been completely elucidated, it seems likely that the release of vasoactive substances secreted by the ovaries under human chorionic gonadotrophin (hCG) stimulation may play a key role in triggering this syndrome. 3 Vascular endothelial growth factor (VEGF), also known as vascular permeability factor, has emerged as one of the factors most likely involved in the pathophysiology of OHSS.4 and 5

Presentation and complications

The clinical manifestations of ovarian hyperstimulation syndrome originate from the combination of decreased intravascular space and the accumulation of protein-rich fluid into body cavities and interstitial space. This ‘third spacing’ causes depletion of the intravascular space. Loss of intravascular volume leads to haemodynamic changes manifested as hypotension, severe tachycardia, and decreased renal perfusion as well as haemoconcentration. Loss of intravascular volume combined with decreased renal perfusion results in electrolyte abnormalities (e.g. hyperkalaemia, hyponatraemia), increase in haematocrit and white cell count, and decrease in creatinine clearance. Accumulation of fluid in the peritoneal cavity leads to abdominal distention and discomfort.

Pulmonary function may be compromised as enlarged ovaries and ascites restrict diaphragmatic movement. Pleural effusions are present in 21% of OHSS cases. 6 Although pleural effusion is generally thought to be a consequence of pronounced ascites, associated with a shift of liquid from the peritoneal cavity to the pleura, isolated pleural effusion without concomitant ascites has been reported as the only symptom of OHSS. 7

Hepatic manifestations are present in about one-quarter of OHSS cases, generally in association with severe OHSS, and disappear with the recovery from OHSS. 6 The presence of liver dysfunction in severe OHSS was associated with a lower clinical pregnancy rate. 8

Thromboembolic events are serious complications of OHSS. The incidence of venous thromboembolism in relation to in-vitro fertilisation (IVF) has been reported in about 0.1% of treatment cycles. 9 According to data from relatively few cases, the venous thromboembolism risk associated with OHSS is reported to be between 0.8% and 2.4%.10 and 11Pregnancies with fresh IVF cycles complicated by OHSS were at a 100-fold increased risk of venous thromboembolism in the first trimester, compared with the background population. 12 A hypercoagulable state is most likely caused by haemoconcentration and hypovolaemia resulting from third spacing and fluid shift. It is also related to increased oestrogen levels.

Severe OHSS is associated with a higher likelihood of pregnancy and multiple gestations. The influence of OHSS on the outcome of the pregnancy remains difficult to appreciate. Data on the relation of OHSS and pregnancy complications are insufficient.13, 14, and 15

Accidents of the hyperstimulated ovary, such as torsion or rupture, are rare but recognised complications. 16 Ovarian hyperstimulation syndrome, particularly if associated with pregnancy, may be by itself a risk factor for ovarian torsion. 17 Life-threatening complications of OHSS include renal failure, hypovolaemic shock, adult respiratory distress syndrome, haemorrhage from ovarian rupture, and thromboembolic episodes. 18

Classification of ovarian hyperstimulation syndrome

The OHSS has traditionally been classified as mild, moderate, or severe. The most popular classification system for staging OHSS is that of Golan el al. 19 This system incorporated the use of transvaginal sonography for both estimating of ovarian enlargement and detection of ascitic fluid. The detection of ascites establishes the diagnosis of moderate OHSS. Subsequent modifications defined a group of critical or complicated OHSS and added to the severe category of the syndrome.20 and 21

The Practice Committee of the American Society for Reproductive Medicine proposed a simplified classification of the syndrome into mild, worsening, and serious. 18 Progression of illness is recognised when symptoms persist, worsen, or include ascites that may be demonstrated by increasing abdominal girth or ultrasound evaluation. Serious illness was defined by the presence of abdominal pain plus one or of the following signs: rapid weight gain, tense ascites, haemodynamic instability, respiratory distress, progressive oliguria, and laboratory abnormalities. Laboratory criteria for women with serious illness include the following: haemoconcentration (haematocrit > 45%), leukocytosis (white blood cell count > 15,000), sodium less than 135 mEq/L, potassium of more that 5.0 mEq/L, elevated liver enzymes, and serum creatinine of more than 1.2 mg/dL. According to the Practice Committee, most people with serious illness require hospitalisation.

It should be remembered that OHSS is a dynamic situation. The clinical symptoms and signs of OHSS are broad in scope and severity, and can defy attempts at specific classification. A person with moderate OHSS may progress within hours or days to a severe case. Therefore, clinicians have to be cautious in monitoring moderate or even mild OHSS.

A division of OHSS into ‘early’ and ‘late’, depending on the time of onset, may be useful in determining the prognosis. 22 Ovarian hyperstimulation syndrome presenting within 9 days after the ovulatory dose of hCG is likely to reflect excessive ovarian response and the precipitating effect of exogenous hCG administered for final follicular maturation. Ovarian hyperstimulation syndrome presenting after this period reflects endogenous hCG stimulation from an early pregnancy. 22 Late OHSS is more likely to be severe and to last longer than early OHSS.

Steps to minimise risk

The prevention of OHSS includes three main strategies: identification of women at risk, using different ovulation-induction strategies before stimulation, and preventive therapy modalities during stimulation ( Table 1 ). The combined use of a gonadotrophin-releasing hormone (GnRH) antagonist protocol with GnRH agonist triggering and oocyte and embryo freezing has considerable promise in preventing OHSS. 23

Table 1 Strategies for preventing ovarian hyperstimulation syndrome.

Identification of women at risk  
Using different ovulation-induction strategies Individually tailored gonadotrophin regimen

GnRH antagonist protocol

In-vitro maturation

Preventive therapy modalities during stimulation Cycle cancellation

Coasting (withholding gonadotrophins)

Administration of intravenous albumin and hydroxyethyl starch

Triggering ovulation by low-dose of hCG

GnRH agonist to trigger final oocyte maturation

Avoidance of hCG for luteal support

Cryopreservation of all oocytes and embryos

Dopamine agonist therapy

Low-dose aspirin therapy

GnRH, gonadotrophin-releasing hormone; hCG, human chorionic gonadotrophin.

Identification of women at risk

Recognising risk factors of OHSS is the key to prevention. All women undergoing ovarian stimulation should be considered at risk of OHSS. Women at higher risk of developing OHSS include young age, low body weight, polycystic ovary syndrome (PCOS), use of GnRH agonists, higher doses of exogenous gonadotrophins, high absolute or rapidly rising serum oestradiol levels, development of multiple follicles during treatment, exposure to hCG, and previous episodes of OHSS.17 and 18Pregnancy increases the likelihood, duration, and severity of OHSS symptoms. An earlier study had reported an OHSS rate of 37% in women with PCOS, whereas the rate was 15% in women without PCOS. 10 Ovarian stimulation in women with PCOS needs to be individually tailored and closely monitored.

A systematic review and meta-analysis of the existing literature 24 showed that both anti-Müllerian hormone and antral follicle count are accurate predictors of excessive response to ovarian hyperstimulation. Measurement of basal serum anti-Müllerian hormone and antral follicle count can be used to determine the women who are high risk for OHSS.25 and 26

Using different ovulation-induction strategies

Individually tailored gonadotrophin regimen

Gonadotrophins can be used for induction of ovulation in anovulatory women or ovarian stimulation for intrauterine insemination or IVF. The differences in the objectives of these three forms of treatment were single follicle for induction of ovulation in anovulatory women, two to three follicles in intrauterine insemination and six to 10 follicles in IVF. Ovarian hyperstimulation syndrome can occur in both induction of ovulation and ovarian stimulation for assisted reproduction. The choice of the gonadotrophin starting dose is an important parameter to prevent the onset of OHSS. It is recognised that reducing the starting dose to 100 IU follicle-stimulating hormone (FSH) or even 75 IU per day in high-risk women could minimise the risk of OHSS. 27 Unfortunately, the syndrome may occur even in women who receive small starting doses. 28

The basis of the classic chronic, low-dose, step-up protocol is to identify the threshold dose that is necessary to induce follicular maturation, especially in women suffering from PCOS. 29 The protocol normally starts with a dose of 75 IU daily for 14 days, followed by small stepwise increases (37.5 IU or less) for a period of 7 days. The dose can again be increased after this period if there is no response. Chronic low-dose step-up gonadotrophin is more useful for induction of ovulation.

The aim of the step-down protocol 30 is to rapidly achieve the FSH threshold for stimulating follicle development, and thus step-down regimens normally begin with a dose of 150 IU FSH daily followed by reduction of the dose once the initial response is established. Both low-dose, step-up and step-down protocols have been shown to help reduce the risk of over-response associated with a lower incidence of OHSS. 31

The use of the gonadotrophin-releasing hormone antagonist protocol

The use of GnRH antagonist protocol resulted in a more physiological approach to ovarian stimulation, leading to fewer side-effects and complications than the long-agonist protocol. Additionally, when using GnRH antagonist protocol, one may induce oocyte maturation with GnRH agonists. This issue will be discussed later. A Cochrane review 32 concluded that the use of antagonist compared with long GnRH agonist protocols was associated with a large reduction in OHSS, with no evidence of a difference in live-birth rates. The data, however, are inconclusive from a recent systematic review and meta-analysis, 33 which investigated whether GnRH antagonist protocols reduce the risk of OHSS in women with PCOS undergoing IVF compared with the long agonist protocol. This review included nine randomised-controlled trials (RCTs) with a total of 966 women with PCOS, and showed no significant difference in the incidence of severe OHSS with the antagonist group compared with the long-agonist group. The incidence of moderate and severe OHSS, when combined together, is reduced with the GnRH antagonist protocol compared with the GnRH long agonist protocol.

In-vitro maturation of oocytes

Although the pregnancy and implantation rates of in-vitro maturation (IVM) treatment are not as high as conventional IVF treatment, immature oocyte retrieval followed by IVM is a promising potential treatment option for infertile women with PCOS, because this group of women are extremely sensitive to stimulation with exogenous gonadotrophins and is at increased risk of developing OHSS. 34 It has been shown that priming with FSH or hCG before immature oocyte retrieval improved oocyte maturation and pregnancy rates. 35 Therefore, IVM treatment represents an attractive alternative to cycle cancellation, coasting, or embryo cryopreservation.


In women with PCOS, short-term treatment with metformin did not improve the response to stimulation but it did improve the pregnancy outcome and reduced the incidence of OHSS. 36 A meta-analysis of RCTs showed that the administration of metformin significantly reduced the risk of OHSS. 37 These findings were obtained from four RCTs that included 449 participants with PCOS who were scheduled for IVF cycles. A recent large RCT found that metformin effectively reduces the incidence of OHSS in a high-risk population of women with PCOS who are receiving gonadotrophin for IVF. 38 The action of metformin is still unknown.

Preventive therapy modalities during stimulation

Cycle cancellation

When symptoms of OHSS emerge even before administration of hCG, cycle cancellation should be seriously considered. Cycle cancellation and withholding of hCG is the only guaranteed method for preventing early OHSS. 39 At present, it is less widely used because of the development of the more acceptable strategies such as coasting.

Coasting (withholding gonadotrophins)

Withholding further gonadotrophin stimulation and delaying hCG administration until oestradiol levels plateau or decrease significantly can reduce risks of OHSS. 40 Coasting does not eliminate the risk of OHSS but may reduce the incidence and severity of the condition. According to a recent Cochrane review, 41 no evidence suggested a benefit of using coasting to prevent OHSS compared with no coasting or other interventions. The Cochrane review included only four studies. Their conclusions were based on heterogeneous studies, and these results have to be interpreted with caution.

Initiating coasting depends on both oestradiol levels and numbers and size of follicles. 42 It is generally accepted that coasting should be initiated when the oestradiol level is greater than 3000 pg/mL in the setting of numerous immature follicles (<16 mm) with rapidly increasing oestradiol level.43 and 44Human chorionic gonadotrophin can be given when oestradiol levels drop to a ‘safe’ level (e.g. 3000 pg/mL). Such ‘coasting’ does not adversely affect outcome in IVF cycles unless it is prolonged (more than 3 days). Cycle cancellation should be considered if the duration of coasting exceeds 4 days or if the oestradiol level decreases by more than 30% the day after hCG trigger. 43

Administration of intravenous albumin and hydroxyethyl starch

Prophylactic intravenous administration of 25% albumin (20–50 g) at time of oocyte retrieval has been suggested as a means of reducing risk of OHSS. The most recent Cochrane meta-analysis 46 of eight RCTs suggested that there is limited evidence of benefit from intravenous albumin administration at the time of oocyte retrieval in the prevention or reduction of the incidence of severe OHSS in high-risk women undergoing IVF or intracytoplasmic sperm injection treatment cycles. 45 Another system review and meta-analysis, however, suggested that intravenous albumin administration in high-risk women does not seem to reduce the occurrence of severe OHSS. 46

An alternative to human albumin is hydroxyethyl solution (1000 mL 6% at the time of oocyte retrieval, followed by another 500 mL 48 h later). A recent Cochrane meta-analysis of three RCTs involving 487 randomised women suggested that hydroxyethyl starch markedly decreases the incidence of severe OHSS. 45

Triggering ovulation by low dose of human chorionic gonadotrophin

Although hCG has been the gold standard for ovulation triggering, it is responsible for an increased incidence of OHSS. To date, consensus is lacking over the optimal dose of hCG for final oocyte maturation. A systematic review of all studies that compared the effect of at least two doses of hCG for final oocyte maturation on IVF outcome and on the incidence of OHSS concluded that the clinical outcome were similar between women receiving 5000 or 10,000 IU hCG. The incidence of OHSS was not reduced in the high-risk population even with lower dose of urinary hCG. 47 Owing to the lack of concrete evidence, it is believed that the dose of hCG should be individualised in the same way as the starting dose of gonadotrophins. Good responders need not receive a dose higher than 5000 IU of hCG. A lower dose of hCG may be prudent for women judged to be at high risk for OHSS. 18

Gonadotrophin-releasing hormone agonist to trigger final oocyte maturation

Gonadotrophin-releasing hormone agonist triggering is now a valid alternative to hCG triggering. Agonist triggering offers the possibility to individually tailor the luteal phase support according to the ovarian response to stimulation. 48 Most recent studies have used single doses of the following types of GnRH agonist: either triptorelin 0.2 mg, 49 buserelin 0.5 mg, 50 or leuprolide acetate 1.5 mg. 51 Most studies support supplementation with luteinising hormone activity in addition to standard luteal phase support with oestradiol and progesterone. Luteinising hormone activity could be supplemented in the form of either one bolus of 1500 IU hCG administered on the day of oocyte retrieval, 52 a total of three boluses of hCG (250–500 IU) during the luteal phase, 51 or recombinant luteinising hormone 300 IU administered every second day during the luteal phase until a positive pregnancy test. 49

A recent meta-analysis showed that the modified luteal support has had a significant positive effect on the reproductive outcome after GnRH agonist triggering without an increase in the OHSS rate. 53 Nevertheless, the most optimal luteal phase support still has to be explored. Until the optimal protocol of luteal supplementation is defined, an alterative option is to freeze all oocytes and embryos (so-call ‘freeze-all’) and transfer in subsequent natural or stimulated cycles. 23 The combination of agonist trigger and ‘freeze all’ gives maximum protection and may even result in better implantation. It results, however, in patient inconvenience and additional expense. GnRH agonist triggering should be used in all oocyte donation cycles, owing to a total elimination of OHSS.54 and 55

Avoidance of human chorionic gonadotrophin for luteal support

Luteal support with hCG is associated with a higher risk for OHSS and should be avoided. 56 The use of exogenous progesterone (e.g. 50 mg progesterone in oil intramuscular, 100 mg progesterone vaginal suppositories, or 8% progesterone vaginal gel, daily) for luteal phase support rather than supplemental doses of hCG, may further reduce risks of OHSS. 39 When symptoms of OHSS emerge even before administration of hCG, cycle cancellation and less aggressive stimulation in a subsequent cycle should be seriously considered.

Cryopreservation of all oocytes and embryos

Administration of hCG to trigger ovulation followed by oocyte retrieval and elective freezing of all embryos will not avoid early OHSS but will prevent the development of the late form of OHSS. In a recently updated Cochrane review, however, there is insufficient evidence to support routine cryopreservation. 57 The reviewers concluded that these results have to be interpreted with caution because of the small number of women in the individual studies. Many IVF centres continue to use this method as a way of reducing the risk of OHSS. More research is needed to determine whether using elective cryopreservation of embryos can reduce the rate of severe OHSS in IVF. The true value of cryopreservation for the prevention of OHSS during IVF, however, may be as an adjunct intervention in support of other effective rescue techniques rather than as a stand-alone option.58 and 59

Dopamine agonist therapy

The increase vascular permeability seen in OHSS is primarily caused by ovarian secretion of vascular endothelial growth factor, which activates its receptor (VEGFR-2). Administration of a dopamine or dopamine receptor 2 agonist, inactivates VEGFR-2 and prevents the increase in vascular permeability. 60 Cabergoline 0.5 mg tablet daily starting on the day of hCG injection and continue for 8 days have been shown to reduce the risk of severe OHSS. Recently, a systematic review and meta-analysis of four randomised trials comparing the prophylactic effect of the dopamine agonist, cabergoline, versus no treatment in IVF and intracytoplasmic sperm injection cycles showed that prophylactic treatment with the dopamine agonist, cabergoline, reduces the incidence, but not the severity of OHSS, without compromising pregnancy outcomes. 61

Low-dose aspirin therapy

Low-dose aspirin therapy for prevention of OHSS is based on the theory that superovulation treatment may induce platelet hyperstimulation, which is associated with OHSS, and that aspirin therapy may inhibit this effect. Recently, the low-dose aspirin treatment (100 mg daily, beginning on the first day of ovarian stimulation) was shown to reduce the risk of severe OHSS in a large randomised clinical trial. 62

Management of ovarian hyperstimulation syndrome

The management of OHSS is essentially supportive, aiming at refilling the arteriolar bed, maintaining circulatory haemodynamics and preventing haemoconcentration. 63 Careful maintenance of blood volume, correction of electrolyte imbalances, and relief of secondary complications of ascites and hydrothorax are generally sufficient to support the woman during the severe phase of OHSS.

Outpatient management

Women with mild manifestation of OHSS do not require any specific treatment. Mild ovarian hyperstimulation can develop into moderate or severe disease, especially if conception ensues. Most women with moderate OHSS still can be managed on an outpatient basis, but they require more careful evaluation, including daily weight and abdominal girth measurement, physical and ultrasound examination to detect increasing ascites and to measure ovarian size. Oral fluid intake should be maintained at no less than 1 L per day. Strict bed rest is unwarranted and may increase risk of thromboembolism. Discomfort may be relieved with paracetamol or opiate medications if severe. Non-steroidal anti-inflammatory agents are not recommended because they may compromise renal function in women with OHSS. 17 If symptoms are worsening, weight continues to increase at 1 kg/day or more, or urine output is decreasing (less than 500 mL/day), the woman should be invited back for physical examination, ultrasound, and laboratory evaluation, including haematocrit, electrolytes, and serum creatinine. The women should be aware that her condition may worsen if pregnancy ensues.

An alternative strategy of treatment for OHSS consists of early intervention with paracentesis in outpatient care.64 and 65Smith et al. 64 reported 25 out of 29 (86%) women with severe OHSS who were managed as outpatients with transvaginal paracentesis with no complication. Early intervention to avoid progression, rather than waiting passively, remains an attractive approach that deserves prospective evaluation. Even though severe OHSS can be managed on an outpatient basis, many clinicians still recommend hospitalisation of women presenting with this condition. 63

Hospitalisation management

Women with serious illness or severe OHSS require hospitalisation for more careful monitoring and aggressive treatment. Clinical examination includes an assessment of hydration and cardiorespiratory system. Abdominal circumference and weight should be recorded at admission and daily until resolution. Fluid intake and output should be recorded and monitored on at least a daily basis. Biochemical monitoring should include serum electrolytes, renal and liver function tests, a coagulation profile and blood count. Ultrasonographic examination provides assessment of ovarian size and the presence of ascites, as well as pleural or pericardial effusions. Assay of beta-hCG will help to diagnose pregnancy as early as possible. Pain and ascites can easily mask adnexal torsion, ovarian rupture and acute intra-abdominal haemorrhage. Serial clinical and laboratory evaluations provide the means to monitor progression of illness and to recognise evidence of resolution.

Optimise fluid administration

Maintenance of adequate intravascular volume must always remain the first priority to ensure appropriate tissue and organ perfusion and avoid the development of multi-system organ failure. Women who are hospitalised require intravenous fluid management to address the acute need for volume expansion while also considering the marked increase in vascular permeability. Fluid administration, however, may contribute to the accumulation of ascites.

Rapid initial hydration may be accomplished with bolus of intravenous fluid (1000 ml normal saline) to maintain adequate urine output and reverse haemoconcentration. 63 If urine output response is adequate and haematocrit normalises, switch to dextrose 5% normal saline and maintain at the rate of 125–150 ml/h while monitoring closely every 4 h. If urine output is inadequate in response to fluid bolus and the haematocrit does not reflect a change toward euvolumia, IV crystalloid fluids may be stopped and albumin (25%) in doses of 50 g, infused over 4 h and repeated at 4–12-h intervals as necessary, is an effective plasma expander. 18

Diuretic therapy is usually contraindicated in individuals with haemoconcentration and hypovolaemia, as these people are intravascularly volume depleted secondary to capillary leak. Once the woman is haemodynamically stable and her haemoconcentration state has resolved (haematocrit less than 38%), however, diuretics (e.g. furosemide, 20 mg IV), in combination with colloids, may be considered to mobilise the third-space oedema.

After several days, third-space fluid begins to re-enter the intravascular space, haemoconcentration reverses, and natural diuresis ensues. Intravenous fluids may be tapered as the woman’s oral intake increases. Once the woman can tolerate oral intake and has adequate urine output, she could be discharged at home. Complete resolution typically takes 10–14 days from the onset of initial symptoms.


Current indications for paracentesis are based upon symptomatic complaints of dyspnoea, abdominal distension and pain, or oliguria. Navot et al. 20 suggested that paracentesis is the single most important treatment modality in life-threatening OHSS not controlled by medical treatment. Transvaginal paracentesis can be carried out safely as an outpatient procedure in women with OHSS. 64

Immediately after paracentesis, characteristic haemodynamic changes occur, including decreased intra-abdominal pressure, improved venous return, and improved renal and uterine perfusion. 66 Removal of ascites up to 7.5 L on one occasion and 45 L in total by serial vaginal paracentesis may be safe in women with severe OHSS. 67 Our experience showed that a marked relief of compression symptoms occurred after removing the first 1000 mL of ascitic fluid. 66 Incomplete tapping might result in rapid re-collection of ascites, however, requiring re-tapping.

The placement of a catheter instead of multiple needle paracentesis would permit complete drainage through one intervention, rather than several. Several reports have described the use of an indwelling transabdominal pigtail catheter placement for continuous drainage of ascites in patients with OHSS.68 and 69Percutaneous placement of a pigtail catheter has been shown to be a safe and effective treatment modality for the management of ascites in severe OHSS. 69 It may represent an attractive alternative to multiple paracentesis.


No firm data indicate either the value of diagnostic tests or heparin prophylaxis to prevent thromboembolic complications during controlled ovarian stimulation and in women who develop OHSS. 9 As thromboembolism, however, is a potentially life-threatening complication, thromboprophylaxis should be considered for women who develop moderate-to-severe OHSS. Low-molecular weight heparin (LMWH) should ameliorate the risk of thrombotic complications, and thromboprophylaxis using pregnancy-related low-molecular weight heparin doses (e.g. 40 mg enoxaparin or 5000 IU dalteparin daily) is now part of many recommended treatment protocols. 70 Low-molecular weight heparin has been favoured over unfractionated heparin because of ease of administration and lack of monitoring needed. In women who do not conceive, thromboprophylaxis may be discontinued with resolution of OHSS. For women who do conceive, continuation until the end of the first trimester, 12 or even longer, depending on the presence of additional risk factors and course of the OHSS. If, however, an early pregnancy has been diagnosed in the woman with critical complications of OHSS, the pregnancy may need to be terminated to prevent further deterioration of her condition.

Intensive care

Intensive care may be required for managing thromboembolic complications, renal failure, or pulmonary compromise that does not respond to supportive care and paracentesis. Renal failure will often respond to low-dose dopamine therapy (0.18 mg/kg/h) that will dilate renal vessels and increase renal blood flow. Intensive monitoring of central venous pressure or pulmonary capillary wedge pressure and even short-term dialysis may be required. Pulmonary intensive care may involve oxygen supplementation, thoracentesis, and assisted ventilation when more conservative measures fail. If a pregnancy is maintaining a life-threatening OHSS, termination of pregnancy must be considered.

Surgical care

Surgical management is necessary only in extreme cases, such as in the case of a ruptured ovarian cyst with haemorrhage, torsion, or an ectopic pregnancy.


Experience with ovulation-induction therapy and knowledge of OHSS pathophysiology and clinical features are key to preventing and managing OHSS. The combined use of a GnRH antagonist protocol with GnRH-agonist triggering and oocyte and embryo freezing eliminates or minimises the occurrence of OHSS in women who are high risk. Women with severe OHSS require hospitalisation for more careful monitoring and treatment. Transvaginal paracentesis can be used as an outpatient treatment to prevent the need for hospitalisation. The inhibition of vascular permeability seems to be a new therapeutic approach to preventing and treating OHSS. In a rat OHSS model, vascular permeability and VEGF expression are dramatically reduced after an hCG antagonist treatment. 71 Perhaps in the future, hCG antagonist may represent a novel treatment for OHSS.

Practice points


  • GnRH antagonist cycles are associated with a lower risk of OHSS and should be the protocol of choice in women who are high risk.
  • GnRH agonist triggering combined with oocyte and embryo freezing eliminates or minimises the occurrence of OHSS in women who are high risk.
  • Women with severe OHSS require hospitalisation for more careful monitoring and treatment.
  • Transvaginal paracentesis can be used as an outpatient treatment to prevent the need for hospitalisation.
Research agenda


  • A better understanding of the pathogenesis of OHSS should facilitate the ability to prevent and treat this serious condition.
  • The inhibition of vascular permeability seems to be a new therapeutic approach to preventing and treating OHSS.
  • To develop an hCG antagonist that could potentially reduce the effects of hCG and limit OHSS.

Conflict of interest

None declared.


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Department of Obstetrics and Gynaecology, National Taiwan University Hospital and National Taiwan University College of Medicine, 8, Chung-Shan South Road, Taipei, Taiwan

Corresponding author. Tel.: +886 2 2312 3456x71511; Fax: +886 2 2311 9765.