What is the role of cervical elastography in evaluating preterm labor risk in pregnant women with risk factors such as prior preterm birth, short cervical length, uterine anomalies, or prior cervical surgery?

Cervical Elastography for Preterm Labor Risk Assessment

Cervical elastography should NOT be used routinely for preterm labor risk assessment in clinical practice, as it remains an investigational technique lacking normal reference values and insufficient evidence to support its clinical utility. 1

Current Guideline Position

The American College of Radiology (ACR) Appropriateness Criteria explicitly states that there are currently insufficient data to recommend cervical elastography use in routine screening for preterm birth in both low-risk and high-risk women, suspected preterm labor, and predicting successful induction of labor. 1

Key Limitations Preventing Clinical Use:

• Lack of standardized normal reference values across gestational ages 1
• No established technical standards for performing the examination 1
• Investigational status - the technique has not been validated for clinical decision-making 1
• Insufficient evidence base despite some promising preliminary data 1

What the Evidence Shows (But Doesn't Change Recommendations)

While elastography measures cervical tissue stiffness—a theoretically useful parameter since cervical softening precedes delivery—the research remains preliminary:

Strain Elastography Studies:

Recent research using the E-Cervix application has shown some associations with preterm birth risk. In a 2021 prospective cohort of 742 women at 18-22 weeks, the elasticity contrast index was associated with increased spontaneous preterm birth risk (OR 1.15,95% CI 1.02-1.30), though other elastography parameters showed no significant association. 2

In women with threatened preterm labor, a 2022 study found that those who delivered preterm had significantly lower hardness ratios compared to those delivering at term, with hardness ratio <50% or <35% identifying higher-risk groups. 3

Technical Challenges:

• Two competing approaches exist: strain elastography (provides only relative stiffness values) versus shear wave elastography (theoretically more objective but technically limited) 4
• No uniformed methodological technique has been established across studies 5
• Intraobserver reliability varies by parameter measured (poor to excellent depending on which cervical zone is assessed) 2

What You Should Use Instead

Transvaginal ultrasound cervical length measurement remains the gold standard for preterm birth risk assessment in all clinical scenarios where imaging is indicated. 1

Established Cervical Length Thresholds:

• <25 mm before 24 weeks: Increased preterm delivery risk in asymptomatic women 1
• ≥30 mm in symptomatic women: Very low risk of delivery within 48 hours to 7 days 6
• ≤15 mm with threatened preterm labor: 66.7% delivered spontaneously <35 weeks versus 13.5% with longer cervix 1

High Negative Predictive Value:

The greatest clinical utility of transvaginal cervical length is its high negative predictive value—a normal cervical length effectively rules out imminent preterm delivery, even in symptomatic women. 1

Clinical Algorithm for Cervical Assessment

For High-Risk Women (prior preterm birth, short cervix, uterine anomalies, cervical surgery):

1. Perform transvaginal ultrasound cervical length screening at 18-24 weeks 1
2. If <25 mm: Consider interventions (vaginal progesterone, cerclage, or pessary depending on history) 1
3. Do NOT add elastography—it provides no validated additional information 1

For Suspected Preterm Labor:

1. Transvaginal ultrasound is the preferred imaging approach for complete visualization of the cervix including the internal os 1
2. Assess cervical length and presence of funneling (funneling is an independent predictor of delivery <37 weeks) 1
3. Transperineal ultrasound is an acceptable alternative if transvaginal is declined or contraindicated (e.g., placenta previa, suspected PPROM) 1

Common Pitfalls to Avoid

• Do not order elastography thinking it adds clinical value—current evidence does not support changing management based on elastography findings 1
• Do not substitute elastography for cervical length measurement—length assessment remains the validated standard 1
• Do not use transabdominal ultrasound alone for suspected preterm labor—it is inadequate for assessing the internal os where preterm changes begin 1

Future Potential (Not Current Practice)

Elastography may eventually prove useful as cervical biomechanical assessment could theoretically complement morphological cervical length measurements. 5, 7 However, significant technical standardization and validation studies are required before clinical implementation. 4, 5 Until normal reference ranges, standardized acquisition protocols, and outcome-based validation studies are completed, elastography should be considered a research tool only. 1