What is the first-line imaging in suspected postpartum hemorrhage (PPH)?

First-Line Imaging for Suspected Postpartum Hemorrhage

Pelvic ultrasound (transabdominal and transvaginal with Doppler) is the imaging modality of choice for the initial evaluation of postpartum hemorrhage. 1

Rationale for Ultrasound as First-Line

The American College of Radiology Appropriateness Criteria definitively establishes ultrasound as the primary imaging modality because it provides rapid, bedside assessment without radiation exposure in the acute postpartum setting 1. This recommendation applies to both early PPH (within 24 hours) and late PPH (24 hours to 6 weeks postpartum) 1.

Ultrasound effectively identifies the most common causes of PPH that require imaging confirmation:

• Retained products of conception (RPOC): Doppler improves specificity and negative predictive value by detecting vascularity within a thickened endometrial echo complex 1
• Vascular abnormalities: Color and spectral Doppler can detect the swirling or yin-yang pattern of blood flow within pseudoaneurysms 1
• Hematomas: Transabdominal approach visualizes bladder flap and subfascial collections 1
• Uterine structural abnormalities: Can assess for uterine rupture, dehiscence, and inversion 2

When to Escalate Beyond Ultrasound

CT angiography (CTA) of the abdomen and pelvis becomes appropriate when:

• Ultrasound findings are inconclusive and hemorrhage persists despite medical management 1
• Active ongoing hemorrhage needs localization for potential angiographic intervention 1
• Intra-abdominal hemorrhage or postsurgical complications are suspected in hemodynamically stable patients 1
• Persistent hemorrhage continues after empiric embolization 1

CTA demonstrates active extravasation in 41-74% of PPH cases with 97% accuracy for detecting the bleeding site when multiphasic technique (noncontrast, arterial, and portal venous phases) is used 1.

Role of MRI

MRI is not commonly used in acute, life-threatening early PPH due to limited access and longer acquisition times 1. However, MRI has specific utility for:

• Distinguishing uterine dehiscence from rupture when ultrasound or CT findings are confusing, given its superior soft-tissue contrast 1
• Localizing deep-seated pelvic hematomas (supralevator versus infralevator) for targeted intervention 1
• Evaluating suspected endometritis with associated abscess or infected hematoma 1

Critical Pitfalls to Avoid

Common ultrasound interpretation errors include:

• Absence of vascularity does not exclude RPOC, as avascular RPOC can occur 1
• Marked vascularity can mimic pseudoaneurysm, though RPOC typically extends to the endometrium while pseudoaneurysm is restricted to myometrium 1
• Distinguishing acquired vascular uterine abnormalities from subinvolution of placental bed vessels is difficult and cannot reliably predict need for intervention 1
• Endometrial debris and gas are relatively common (20-25%) in the early postpartum period, and thickened endometrial echo complex up to 2-2.5 cm is nonspecific 1

For CTA interpretation:

• Dilated tortuous hypertrophic uterine arteries can mimic active extravasation (false positive) 1
• Slow intermittent hemorrhage from atony may not be detected (false negative) 1

Clinical Context Matters

Remember that uterine atony accounts for 70-80% of all PPH cases and is primarily a clinical diagnosis 3. Most causes of PPH can be diagnosed clinically, but imaging plays an important role when the diagnosis is unclear or when specific anatomic information is needed for intervention planning 1.