USG in Antenatal period

Ultrasound is the primary tool for detecting prenatal anomalies, allowing early identification of structural malformations, guiding further investigations, and enabling timely counseling and management.

Principles of Ultrasound in Prenatal Anomaly Detection

• Safe, non-invasive, real-time imaging using high-frequency sound waves.
• Provides detailed information on fetal anatomy, growth, position, and amniotic fluid.
• Can be repeated multiple times during pregnancy without radiation risk.

Timing of Key Scans

• First-trimester scan (11–13 weeks): DATING SCAN

  • Detects major anomalies like acrania, holoprosencephaly, large encephalocele, ectopia cordis, exomphalos, gastroschisis, body stalk anomaly1.
  • Early detection of open spina bifida and major cardiac defects is possible with improved protocols1.

• Second-trimester anomaly scan (18–22 weeks): ANOMOLY SCAN

  • Gold standard for systematic evaluation of fetal organs
  • Detects CNS malformations, cardiac defects, facial clefts, abdominal wall defects, renal anomalies, skeletal dysplasias.
  • Uses four-chamber view of heart, outflow tracts, mid-sagittal brain sections, and facial views for comprehensive assessment1.

• Third-trimester scan (28–40 weeks): GROWTH SCAN

  • Monitors growth restriction, late-onset anomalies, and evolving conditions (e.g., hydrocephalus, bowel obstruction).

Advances in Ultrasound Technology

• High-resolution transducers improve visualization of subtle defects.
• Color Doppler enhances cardiac evaluation.
• 3D/4D ultrasound provides spatial views of face, limbs, and spine.
• Spatiotemporal Image Correlation (STIC) and Fetal HQ improve fetal echocardiography1.
• Artificial intelligence integration is emerging to enhance detection rates

Limitations

• Detection rates vary with gestational age, maternal habitus, fetal position, and operator expertise.
• Some anomalies (e.g., metabolic disorders, mild structural defects) may not be detected prenatally.
• False positives can occur, requiring correlation with genetic testing (amniocentesis, chorionic villus sampling) or MRI.

Notes on Key Prenatal Ultrasound Scans

• Dating Scan (11–14 weeks):

  • Confirms gestational age by measuring crown-rump length (CRL).
  • Assesses viability and number of fetuses.
  • Screens for major early anomalies and nuchal translucency for chromosomal risk.

• Anomaly Scan (18–22 weeks):

  • Detailed systematic evaluation of fetal anatomy.
  • Detects structural anomalies in brain, heart, face, abdomen, limbs, and spine.
  • Assesses placenta, amniotic fluid, and fetal growth parameters.

• Growth Scans (Third trimester, 28–40 weeks):

  • Monitor fetal growth and well-being.
  • Detects intrauterine growth restriction (IUGR) or macrosomia.
  • Evaluates amniotic fluid volume and Doppler studies for fetal circulation.