Ovarian Hyperstimulation Syndrome (OHSS): Ultrasound Diagnosis After IVF, Imaging Findings and Treatment
A Radiologist’s Case-Based Guide to Recognizing a Potentially Dangerous IVF Complication
Introduction: When “Normal” Post-IVF Bloating Is No Longer Normal
A 31-year-old woman undergoes in vitro fertilization (IVF), hoping that years of infertility treatment will finally lead to pregnancy.
Several days after ovarian stimulation, however, something changes.
Her abdomen begins to feel unusually tight.
The bloating becomes progressively worse.
Then abdominal pain develops.
At first, it may be tempting to interpret these symptoms as a temporary consequence of fertility treatment. After all, ovarian stimulation intentionally causes the ovaries to enlarge and multiple follicles to develop.
But there is a critical distinction between expected ovarian response and ovarian hyperstimulation syndrome (OHSS).
The attached case describes a 31-year-old woman following IVF who developed rapid abdominal distension and pain, with ultrasound demonstrating markedly enlarged bilateral ovaries containing numerous cystic follicles.
This is the point at which imaging becomes more than a diagnostic exercise.
It becomes a tool for risk recognition.
OHSS is not simply a condition in which “the ovaries become large.” Its underlying pathophysiology involves increased vascular permeability, intravascular volume depletion, hemoconcentration, ascites and, in severe cases, pleural effusion, renal dysfunction, thrombosis and respiratory compromise.
For radiologists, emergency physicians, gynecologists and fertility specialists, the central question is therefore not:
“Are the ovaries enlarged?”
The more important question is:
“Does the imaging pattern indicate a systemic complication of ovarian stimulation?”
That distinction can change clinical management.
1. Clinical Background: What Is Ovarian Hyperstimulation Syndrome?
Ovarian hyperstimulation syndrome is a potentially serious complication associated with assisted reproductive technology (ART), particularly controlled ovarian stimulation during IVF.
During fertility treatment, gonadotropins are administered to stimulate the development of multiple ovarian follicles. Ovulation is subsequently triggered, traditionally with human chorionic gonadotropin (hCG) in many stimulation strategies.
In susceptible patients, the ovarian response becomes excessive.
The attached case material emphasizes VEGF as an important mediator. Increased vascular permeability allows fluid and protein to move from the intravascular compartment into the extravascular space.
This is why OHSS should not be regarded simply as a localized gynecologic abnormality.
It is a systemic vascular permeability syndrome associated with ovarian stimulation.
The 2024 American Society for Reproductive Medicine (ASRM) guideline specifically addresses the prevention of moderate and severe OHSS and identifies it as a serious complication associated with ART.
2. The Patient: A Typical Imaging Presentation After IVF
Consider the clinical sequence in the attached case.
A 31-year-old woman undergoes IVF treatment.
Following ovarian stimulation, she develops:
- Rapid abdominal distension
- Lower abdominal pain
- Progressive abdominal tightness
- Increasing body weight
- Possible nausea or vomiting
- Reduced urine output
- Potential respiratory symptoms if the disease progresses
The source material emphasizes that early symptoms may resemble expected post-procedure discomfort. This creates an important diagnostic trap: the patient may initially normalize her symptoms because they occur after fertility treatment.
For this reason, the temporal relationship between IVF and new or rapidly progressive abdominal symptoms is itself clinically important.
The imaging request should not simply read:
“Pelvic ultrasound after IVF.”
The radiologist should understand the clinical question:
“Could this represent OHSS, and is there imaging evidence of progression or complication?”
3. Why Ultrasound Is the First-Line Imaging Modality
For suspected OHSS, ultrasound is particularly valuable because it simultaneously evaluates the ovaries and the consequences of systemic fluid redistribution.
The attached case identifies ultrasound as the key imaging modality because it:
- avoids ionizing radiation,
- can be repeated,
- measures ovarian enlargement,
- demonstrates multiple follicles or cystic changes,
- detects ascites,
- and supports longitudinal follow-up.
This is especially relevant in reproductive-age patients, where minimizing unnecessary radiation exposure is desirable.
The 2023 RadioGraphics multimodality review similarly emphasizes that radiologists need to recognize both expected and abnormal ovarian appearances during ART, because stimulated ovaries can normally appear enlarged and contain numerous cystic follicles. Importantly, the same population can develop emergencies such as OHSS and ovarian torsion.
That creates the first major interpretive challenge:
Not every enlarged ovary after IVF represents OHSS.
The radiologist must integrate:
clinical symptoms + stimulation history + ovarian morphology + ascites + extra-pelvic findings.
4. Figure 1 — Ultrasound: The Central Imaging Pattern
Figure 1. Ultrasound appearance of ovarian hyperstimulation syndrome after IVF. Bilateral ovarian enlargement with numerous cystic follicles is demonstrated.
The attached case describes transverse ultrasound imaging showing markedly enlarged bilateral ovaries containing numerous cystic follicles. The ovarian parenchyma is compressed toward the periphery by multiple fluid-filled follicular structures.
Radiologic Interpretation
The dominant pattern is:
Bilateral ovarian enlargement + numerous cystic follicles + recent ovarian stimulation.
The bilateral nature is particularly important.
An enlarged ovary with a complex cystic appearance can have a broad differential diagnosis. However, when both ovaries are markedly enlarged and contain multiple follicles in the setting of recent IVF, OHSS rises substantially on the differential diagnosis.
Key Imaging Pearls
- Bilateral ovarian enlargement
- Numerous cystic follicles
- Relatively symmetric ovarian involvement
- Stimulated ovarian morphology
- Assessment for pelvic free fluid/ascites
- Assessment for additional complications
The attached case specifically identifies bilateral ovarian enlargement, multiple follicular cysts, and a history of ovarian stimulation as key diagnostic clues.
5. Figure 2 — Ultrasound: Multiple Follicles and the “Necklace” Pattern
Figure 2. Transverse pelvic ultrasound demonstrating enlarged ovaries containing numerous cystic follicles. The follicles are distributed within the enlarged ovarian parenchyma in the setting of recent ovarian stimulation.
The second ultrasound image in the case demonstrates an enlarged left ovary containing multiple cystic follicles. The source describes a peripheral follicular arrangement as a “Necklace Sign”, interpreted in the case context as evidence of an exaggerated ovarian response.
From a radiology perspective, however, this finding should not be interpreted in isolation.
A follicular arrangement may overlap with appearances encountered in other ovarian stimulation states, including polycystic ovarian morphology. The decisive information comes from the clinical context and the broader imaging pattern.
The key question is not:
“Is there a necklace-like arrangement?”
but rather:
“Does the complete clinical-imaging pattern support OHSS?”
6. The Five-Point OHSS Ultrasound Checklist
A practical ultrasound interpretation can be standardized into five questions.
1. How large are the ovaries?
Ovarian enlargement provides a basic indicator of the ovarian response.
2. How many follicles are present?
A large number of cystic follicles supports an exaggerated ovarian response in the appropriate clinical setting.
3. Is ascites present?
Ascites is particularly important because it reflects the systemic fluid shift associated with increased vascular permeability.
4. Is there evidence of pleural effusion?
Pleural effusion raises concern for more significant systemic involvement.
5. Are the findings bilateral?
Bilateral involvement supports an ovarian stimulation-related process and helps distinguish OHSS from some focal ovarian abnormalities.
The attached case explicitly organizes these five elements—ovarian size, follicle number, ascites, pleural effusion and bilaterality—as core imaging considerations.
7. Ascites: The Imaging Finding That Changes the Clinical Conversation
One of the most important transitions in OHSS is the appearance or progression of ascites.
The enlarged ovaries are visually striking, but ovarian size alone does not determine disease severity.
The more important question is whether the vascular permeability process is producing significant third spacing.
Ascites provides an imaging window into this process.
A patient with enlarged ovaries but minimal or no ascites may have a substantially different clinical trajectory from a patient with:
- markedly enlarged ovaries,
- increasing ascites,
- pleural effusion,
- progressive abdominal distension,
- oliguria,
- hemoconcentration.
The attached case emphasizes that increasing ascites indicates movement of fluid into the abdominal cavity and warrants closer clinical monitoring.
8. CT Imaging: Useful, but Not the First Test
A common mistake in modern imaging practice is to assume that CT is automatically superior because it provides comprehensive anatomical coverage.
For OHSS, that is not the correct approach.
The attached case explicitly states that CT is not recommended as the primary imaging test in most cases. Ultrasound is generally sufficient for diagnosis and follow-up. CT becomes useful when:
- the cause of abdominal pain is unclear,
- complications are suspected,
- or another acute abdominal process needs to be excluded.
When CT is performed, the radiologist should evaluate:
- bilateral ovarian enlargement,
- multiple low-attenuation cystic structures,
- ascites,
- pleural effusion,
- mesenteric edema,
- perihepatic fluid,
- pelvic fluid.
This is particularly important in emergency presentations where the differential diagnosis extends beyond OHSS.
For example, a patient after IVF who presents with severe abdominal pain could also have:
ovarian torsion, ectopic pregnancy, hemorrhagic ovarian pathology, bowel disease, infection or another acute abdominal process.
CT should therefore be viewed as a problem-solving modality, not as the routine first-line examination for uncomplicated suspected OHSS.
9. MRI: The Problem-Solving Examination
MRI has a more selective role.
The attached case identifies several situations in which MRI may be useful:
- suspected ovarian tumor,
- suspected hemorrhagic cyst,
- possible ovarian torsion,
- equivocal ultrasound findings.
MRI provides excellent soft-tissue characterization and can help determine whether a complex ovarian lesion contains:
- blood products,
- solid components,
- enhancing tissue,
- or other features that require a different diagnostic pathway.
Again, the key principle is appropriate modality selection.
The best radiologist is not the one who orders the most sophisticated test.
The best radiologist is the one who identifies the least invasive test capable of answering the clinical question accurately.
10. Differential Diagnosis: What Can Mimic OHSS?
OHSS vs Polycystic Ovary Syndrome
Polycystic ovarian morphology may demonstrate numerous follicles.
However, PCOS does not typically produce the acute clinical syndrome of rapidly progressive abdominal distension, significant ascites, and systemic fluid redistribution described in OHSS.
The temporal association with ovarian stimulation is therefore crucial.
OHSS vs Ovarian Torsion
This is one of the most clinically important distinctions.
Marked ovarian enlargement increases the risk of torsion.
A patient with OHSS can therefore develop secondary ovarian torsion.
Sudden severe unilateral pelvic pain should immediately raise concern.
Doppler assessment of ovarian vascularity can contribute to evaluation, but normal arterial flow does not absolutely exclude torsion.
The attached case specifically emphasizes assessment for abnormal ovarian blood flow when torsion is suspected.
OHSS vs Hemorrhagic Corpus Luteum
Hemorrhagic corpus luteum can produce a complex cystic appearance.
However, it is generally more focal rather than the bilateral, multifollicular ovarian enlargement characteristic of the case.
OHSS vs Ovarian Neoplasm
A bilateral cystic appearance should not automatically be attributed to OHSS.
Solid nodules, irregular walls, suspicious vascularity or atypical morphology should prompt further evaluation.
The attached case emphasizes that ovarian neoplasm cannot be completely excluded merely because multiple cystic structures are present.
11. When OHSS Becomes Dangerous
The clinical danger of OHSS comes from its systemic consequences.
The attached case describes a progression involving:
vascular permeability
→ fluid shift
→ intravascular depletion
→ hemoconcentration
→ renal hypoperfusion
→ oliguria
→ thrombotic risk
with possible respiratory complications from pleural effusion.
This explains why a patient can simultaneously have:
too much fluid outside the blood vessels
and
too little effective circulating volume inside the blood vessels.
This apparent paradox is fundamental to understanding OHSS.
12. Mild, Moderate and Severe OHSS: Imaging Perspective
Mild OHSS
The patient may have:
- ovarian enlargement,
- multiple follicles,
- minimal abdominal symptoms,
- little or no significant ascites.
The attached case notes that many mild cases can be managed conservatively with monitoring.
Moderate OHSS
The imaging pattern may demonstrate:
- significant bilateral ovarian enlargement,
- numerous follicles,
- increasing pelvic fluid/ascites.
The clinical team must then consider volume status, renal function and electrolyte abnormalities.
Severe OHSS
Severe disease can include:
- marked ovarian enlargement,
- large-volume ascites,
- pleural effusion,
- vascular compression,
- renal dysfunction,
- respiratory compromise,
- thromboembolic complications.
The attached case emphasizes that severe disease may require urgent hospitalization and intensive monitoring.
13. A Critical Radiology Insight: Ovarian Size Is Not the Whole Story
One of the most important teaching points from this case is that ovarian size should never be interpreted as an isolated severity marker.
A very large ovary may look dramatic on ultrasound.
But the patient with:
large ovaries + minimal fluid + stable clinical status
is fundamentally different from the patient with:
large ovaries + increasing ascites + pleural effusion + oliguria + hemoconcentration.
The source explicitly states that ovarian size alone does not necessarily correlate with severity; ascites, pleural effusion, clinical symptoms, and laboratory data must also be considered.
This is an important example of why imaging should be interpreted as part of a multimodal clinical decision system, rather than as an isolated diagnostic image.
14. Diagnostic Workflow
A practical OHSS workflow can be represented as:
The attached material emphasizes that follow-up imaging is important because ovarian size, ascites, and other findings may change during treatment.
15. Where Could Artificial Intelligence Fit?
This is where the story becomes particularly interesting.
AI is not currently established in the attached case as a validated diagnostic treatment for OHSS.
Therefore, it would be inappropriate to claim that an AI system can currently diagnose OHSS with a specific accuracy rate based on this case.
However, the workflow provides several potential opportunities for medical imaging AI.
Potential AI Application 1: Automated Ovarian Segmentation
A computer vision model could potentially segment enlarged ovaries on ultrasound and estimate ovarian volume.
Potential AI Application 2: Follicle Detection
An AI model could potentially identify and count multiple follicles automatically.
This could be particularly useful during fertility monitoring, where follicle number and morphology are clinically important.
Potential AI Application 3: Ascites Detection
Computer vision algorithms could potentially detect and quantify free intraperitoneal fluid.
Potential AI Application 4: Longitudinal Monitoring
A future AI system could compare serial examinations:
Day 1 → Day 3 → Day 5 → Day 7
and automatically calculate:
- ovarian volume change,
- follicle burden,
- ascites progression,
- interval change.
Potential AI Application 5: Clinical Decision Support
An enterprise clinical AI platform could theoretically combine:
ultrasound + laboratory values + symptoms + vital signs + IVF treatment parameters
to identify patients who require closer monitoring.
But this represents a future clinical decision-support concept, not a validated standard-of-care OHSS AI solution established by the attached case.
16. The Future: From Image Interpretation to Clinical Intelligence
The next generation of medical imaging AI will likely move beyond simply answering:
“What is in this image?”
Instead, clinical AI systems will increasingly attempt to answer:
“What does this imaging finding mean for this patient right now?”
For OHSS, a future clinical intelligence ecosystem could look like:
The important principle is that AI should augment physician reasoning rather than replace it.
In reproductive imaging, this is especially important because the distinction between expected treatment-related ovarian changes and pathological complications depends heavily on timing, symptoms, and treatment context.
17. Enterprise AI, PACS and Clinical Workflow
From a healthcare IT perspective, OHSS also illustrates a broader problem.
An AI algorithm operating independently from the clinical workflow may detect an enlarged ovary.
But an enterprise clinical AI system could theoretically connect:
- PACS
- ultrasound workstation
- electronic health record
- laboratory information system
- IVF treatment records
- clinical decision support
- radiology reporting
into a unified workflow.
The goal would not simply be:
AI detects enlarged ovary.
The goal would be:
AI identifies a potentially significant imaging pattern and places it into the appropriate clinical context.
This is where enterprise AI platforms, PACS-integrated AI, cloud healthcare infrastructure and clinical decision-support systems become strategically relevant.
However, these technologies should be evaluated on clinical validation, interoperability, cybersecurity, regulatory status, workflow integration and physician oversight—not simply on marketing claims.
18. Follow-Up Imaging: The Story Does Not End With the First Ultrasound
One of the most important points in the attached case is that OHSS requires dynamic assessment.
A single ultrasound examination provides a snapshot.
A follow-up examination provides a trajectory.
The radiologist should ask:
Is the ovarian enlargement decreasing?
Is ascites resolving?
Is pleural effusion improving?
Has a new complication developed?
Is there evidence suggesting ovarian torsion?
The source specifically recommends monitoring ovarian size, cystic changes, ascites, pleural effusion, and possible torsion during follow-up.
This concept is highly relevant to modern medical imaging AI.
A future AI system may ultimately provide greater value through longitudinal change detection than through one-time classification.
19. Ten Key Imaging Pearls Every Radiologist Should Remember
Pearl 1: Recent IVF or ovarian stimulation is a critical clinical clue.
Pearl 2: Bilateral ovarian enlargement is more informative than unilateral enlargement in this context.
Pearl 3: Multiple cystic follicles are a characteristic imaging component of stimulated ovaries.
Pearl 4: Do not diagnose OHSS from ovarian size alone.
Pearl 5: Always search for ascites.
Pearl 6: Pleural effusion should raise concern for more significant systemic involvement.
Pearl 7: Sudden severe pain requires consideration of ovarian torsion.
Pearl 8: CT is generally a problem-solving examination rather than the routine first-line test.
Pearl 9: MRI is useful when ultrasound is equivocal or another ovarian pathology needs characterization.
Pearl 10: Serial imaging can be more clinically meaningful than a single examination.
These points closely reflect the checklist and diagnostic priorities described in the attached case.
20. The Most Important Clinical Lesson
There is a subtle but powerful lesson hidden inside this case.
The most dangerous imaging finding is not necessarily the most visually dramatic one.
An enlarged ovary attracts attention.
But the systemic consequences of vascular permeability determine the patient's risk.
That means the radiologist must move from:
“What do the ovaries look like?”
to:
“What is happening to the entire patient?”
That is the difference between image description and clinical radiology.
21. Prognosis
Most patients with appropriately recognized OHSS recover.
The prognosis depends heavily on the severity of the syndrome and timely management.
The attached case notes that delayed recognition may result in:
- hemoconcentration,
- thromboembolism,
- renal dysfunction,
- respiratory complications,
- and, rarely, life-threatening disease.
Conversely, reduction in ovarian size and resolution of ascites on follow-up imaging may support clinical recovery.
The newest RCOG Green-top Guideline, published in 2026, represents the fourth edition of its OHSS management guideline and provides an important contemporary reference for clinicians managing this complication.
22. What Has Changed in the Modern IVF Era?
The prevention of OHSS has become increasingly important as reproductive medicine moves toward more individualized ovarian stimulation.
The 2024 ASRM guideline specifically focuses on identifying patients at high risk and implementing evidence-based prevention strategies.
The updated ESHRE ovarian stimulation guideline, published in Human Reproduction in 2026, provides 121 recommendations addressing 21 key questions concerning ovarian stimulation for IVF/ICSI.
This represents an important shift:
Modern fertility medicine is increasingly moving from treatment of complications toward prediction and prevention.
Medical imaging is part of that evolution.
23. The Radiologist's Role Is Expanding
The radiologist is no longer simply the person who identifies a lesion.
In complex clinical environments, imaging specialists increasingly contribute to:
- risk stratification,
- treatment monitoring,
- complication detection,
- multidisciplinary decision-making,
- quantitative imaging,
- AI validation,
- clinical workflow design.
OHSS provides an excellent example.
The ultrasound image may show enlarged ovaries.
But the radiologist's report should communicate the clinically meaningful pattern.
For example:
Bilateral markedly enlarged ovaries containing numerous cystic follicles, compatible with the recent history of controlled ovarian stimulation. Associated pelvic free fluid/ascites is present. In the appropriate clinical context, findings are concerning for ovarian hyperstimulation syndrome. Clinical correlation and assessment for systemic complications are recommended.
This type of report moves beyond anatomy toward actionable clinical communication.
24. Frequently Asked Questions
Is ovarian enlargement after IVF always OHSS?
No.
Ovarian enlargement and multiple follicles can be expected during stimulated ovarian cycles. OHSS becomes more concerning when the imaging findings occur together with the appropriate clinical syndrome, particularly progressive abdominal distension, pain, ascites or systemic manifestations.
Is ultrasound enough to diagnose OHSS?
In many cases, yes. The attached case identifies ultrasound as the central imaging modality because it evaluates ovarian size, follicles and ascites without ionizing radiation.
Does every patient with OHSS need CT?
No.
CT is generally reserved for patients with atypical presentations, suspected complications, or an alternative acute abdominal diagnosis.
What is the most dangerous complication?
The systemic consequences of intravascular volume depletion and hemoconcentration can lead to thromboembolism and renal dysfunction.
Does a larger ovary always mean more severe OHSS?
No.
Severity depends on the overall clinical picture, including ascites, pleural effusion, laboratory findings and symptoms—not ovarian size alone.
25. Conclusion
Ovarian hyperstimulation syndrome is one of the most important imaging complications associated with assisted reproductive technology.
The classic imaging pattern is straightforward:
bilateral enlarged ovaries + numerous cystic follicles + appropriate IVF/ovarian stimulation history.
But expert interpretation goes further.
The radiologist must actively search for:
ascites, pleural effusion, vascular complications and ovarian torsion.
The attached case demonstrates why ultrasound remains central to the diagnostic pathway: it is accessible, repeatable, radiation-free and capable of evaluating both ovarian morphology and fluid redistribution.
The deeper lesson is that OHSS is not simply an ovarian imaging abnormality.
It is a systemic vascular permeability syndrome.
That is why the most valuable radiology report is not merely:
“Both ovaries are enlarged.”
It is:
“The imaging pattern is compatible with ovarian hyperstimulation syndrome, and the presence or absence of ascites, pleural effusion and other complications should be communicated because these findings influence clinical risk assessment.”
As IVF becomes increasingly sophisticated, medical imaging will become increasingly quantitative, longitudinal and AI-assisted.
But the fundamental principle will remain unchanged:
Technology can identify patterns. Clinical expertise determines what those patterns mean.
26. Key Takeaways
- OHSS is a systemic complication of ovarian stimulation, not simply ovarian enlargement.
- Ultrasound is the primary imaging modality in suspected OHSS.
- Bilateral enlarged ovaries with multiple cystic follicles are characteristic findings in the appropriate clinical context.
- Ascites is an important marker of systemic vascular permeability.
- Pleural effusion may indicate more significant disease.
- Ovarian torsion must be considered when severe acute pain occurs.
- CT is mainly useful for complications or alternative diagnoses.
- MRI is a problem-solving tool for equivocal or atypical ovarian findings.
- Ovarian size alone does not define disease severity.
- Serial ultrasound can provide important information about disease trajectory.
- AI could potentially automate ovarian segmentation, follicle counting and fluid quantification, but these applications require clinical validation.
- The future of imaging is moving from isolated image interpretation toward longitudinal clinical intelligence.
References
1. ASRM Practice Committee
Practice Committee of the American Society for Reproductive Medicine. “Prevention of moderate and severe ovarian hyperstimulation syndrome: a guideline.” Fertility and Sterility. 2024;121(2):230–245. DOI: 10.1016/j.fertnstert.2023.11.013.
2. RCOG 2026 Guideline
Hamoda H, Drakeley AJ, Brian K, Evbuomwan IO, Mathur R, on behalf of the Royal College of Obstetricians and Gynaecologists. “The Management of Ovarian Hyperstimulation Syndrome Green-Top Guideline No. 5.” BJOG. 2026;133(7):e50–e69.
DOI: 10.1111/1471-0528.70195.
3. Multimodality Imaging Review
Smith KA, Parvinian A, Ainsworth AJ, Shenoy CC, Packard AT. “Normal and Abnormal Appearances of the Ovaries during Assisted Reproduction: Multimodality Imaging Review.” RadioGraphics. 2023;43(11):e230089. DOI: 10.1148/rg.230089.
4. ESHRE 2026 Update
ESHRE Guideline Group on Ovarian Stimulation. “ESHRE guideline: ovarian stimulation for IVF/ICSI: an update in 2025.” Human Reproduction. 2026;41(4):498–514. DOI: 10.1093/humrep/deag018.
5. ASRM Previous Guideline
Practice Committee of the American Society for Reproductive Medicine. “Prevention and treatment of moderate and severe ovarian hyperstimulation syndrome: a guideline.” Fertility and Sterility. 2016;106(7):1634–1647. DOI: 10.1016/j.fertnstert.2016.08.048.
6. Classic OHSS Literature
Golan A, Ron-El R, Herman A, et al. “Ovarian hyperstimulation syndrome: an update review.” Obstetrical & Gynecological Survey. 1989;44:430–440.
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