Diagnostic Testing for Suspected Retained Products of Conception
Transvaginal ultrasound with color Doppler is the initial test of choice for suspected retained products of conception (RPOC). 1, 2
Primary Diagnostic Approach
Perform transvaginal ultrasound as the first-line imaging modality, which should be combined with color and spectral Doppler to assess internal vascularity patterns. 2 The American College of Radiology specifically recommends this approach for diagnosing RPOC. 3
Key Sonographic Findings to Look For:
- Intracavitary tissue with internal vascularity detected on Doppler imaging 1, 2
- Persistent gestational sac following early pregnancy loss 3, 2
- Endometrial mass or focal endometrial thickening, particularly when flow is detected within the endometrial abnormality 1
- Marked diffuse endometrial thickening with vascular flow 1
Important Diagnostic Thresholds
- Endometrial thickness <10 mm has high negative predictive value for incomplete early pregnancy loss, making RPOC unlikely 2
- Vascular flow in the endometrial cavity increases the likelihood that retained tissue is present 2
Critical Pitfalls to Avoid
Do not rely solely on endometrial thickness measurements. Research demonstrates that measurements of endometrial thickness or volume alone are not good tests for diagnosing incomplete miscarriage, as there is no identifiable cut-off that can differentiate between RPOC and decidua. 4 The overall false-positive rate for sonographic diagnosis can be as high as 34%, with even higher rates (51.5%) in postpartum patients. 5
Blood clots and RPOC appear isoechoic on ultrasound, which can lead to false positives and unnecessary interventions. 6 This is why Doppler assessment of vascularity is essential - it helps distinguish vascularized retained tissue from avascular blood clots. 1, 2
Clinical Context Integration
The diagnosis becomes more reliable when ultrasound findings are combined with clinical presentation:
- Continued bleeding after pregnancy loss 1
- Persistent elevation or rise of serum hCG after diagnosis of nonviable pregnancy 1
- Vaginal bleeding and pelvic pain in postpartum or post-abortion patients 7
Special Considerations
In patients with history of cesarean delivery, carefully evaluate for abnormal placentation, as RPOC may represent undiagnosed placenta accreta spectrum disorder. 2 Enhanced myometrial vascularity is common after pregnancy and should not be confused with arteriovenous malformation. 2
For hemodynamically unstable patients with heavy bleeding, immediate surgical evacuation is indicated regardless of ultrasound findings. 2