BACKGROUND AND PURPOSE:

• NICHD recommends 18 to 20 weeks as an ideal time for obstetric ultrasound for fetal anatomy while ISUOG recommends 18 to 22
• Visualization of all required structures may not always be possible
  • Clinical utility and cost-effectiveness of repeat ultrasound to complete the initial evaluation has not been evaluated
• NICHD recommend follow up in 2 to 4 weeks for limited visualization, but if the repeat exam is still incomplete

…the panel agreed that further ultrasonographic examination solely for better visualization is not recommended and should be performed only if there are other indications

• Wood et al. (Amer J Perinatol, 2018) assessed the clinical utility of repeat ultrasound following an incomplete fetal anatomic survey

METHODS:

• Retrospective cohort study
  • Midtrimester anatomic ultrasound
  • Singletons
  • Incomplete ultrasound with repeat exams until completion
• Patients were divided based on when the exam was deemed completed
  • FIRST exam
  • SECOND exam
  • THIRD exam
• The number of ultrasounds needed to detect an anomaly was assessed per group

RESULTS:

• 15,768 ultrasounds were performed on 13,740 patients
  • 11,828 (86%) exams were completed on first attempt
    • Mean GA: 18.5 weeks
  • 1,796 (13%) required a second scan
    • Mean GA: 19.7 weeks
  • 116 (1%) required a third scan or more
    • Mean GA: 20.4 weeks
  • With increasing number of scans, patients were statistically more likely (p<0.001) to have the following
    • Demographics: Older | Black |Government insured
    • Comorbidities: Obesity | Progestational diabetes | Chronic hypertension
  • 324 total anomalies were detected
    • 93.8% in FIRST
    • 5.9% in SECOND
    • 0.3% in THIRD
  • The number of scans needed to detect an anomaly was
    • 39 in the FIRST
    • 189 in the SECOND
    • 348 in the THIRD
  • Overall, the system in which an anomaly was found was usually the same system that was not well seen on the initial evaluation (p = 0.044), especially for
    • Head | Face | Spine | Chest | Heart

CONCLUSION:

• 94% of anomalies are detected in the initial fetal anatomic survey
• The incremental diagnostic yield then decreases, requiring appreciably more repeat scans to detect one anomaly
• The authors state

…given the limited yield for anomaly detection and considering health care resources, we suggest that the use of repeat midtrimester ultrasound for anomaly detection—particularly the use of more than one repeat ultrasound—should be minimized.

Learn More – Primary Sources:

The Utility of Repeat Midtrimester Anatomy Ultrasound for Anomaly Detection

Fetal imaging: Executive summary of a Joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Institute of Ultrasound in Medicine, American College of Obstetricians and Gynecologists, American College of Radiology, Society for Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging Workshop.

Related ObG Topics:

When LMP and Ultrasound Dates Don’t Match: When to Redate?

Mild Cerebral Ventriculomegaly on Prenatal Ultrasound – Next Steps and Clinical Implications