Trisomy Findings on Fetal Ultrasound

Aka: Trisomy Findings on Fetal Ultrasound, Aneuploidy Markers on Second Trimester Ultrasound

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II. Indications: Non-invasively assess trisomy risk

  1. Maternal age over 35 years

III. Efficacy

  1. Trisomy risk Age >35 years
    1. Overall: 1 in 80
    2. With Negative Ultrasound: 1 in 400
  2. Ultrasound detects
    1. Trisomy 18: 100%
    2. Trisomy 21 Test Sensitivity: 50-60%
    3. Least accurate screening for Aneuploidy
      1. Follow positive Ultrasound testing with Second Trimester Quad Screening or Placental Cell-Free DNA

IV. Findings: Soft Markers of Aneuploidy on Second Trimester Ultrasound

  1. Choroid Plexus Cyst
  2. Echogenic intracardiac focus
  3. Clinodactyly
  4. Sandal Gap Toe
  5. Echogenic Bowel
  6. Hypoplastic Nasal Bone
  7. Pyelectasis
  8. Shortened Humerus
  9. Shortened Femur
  10. Single Umbilical Artery
  11. Thickened Nuchal Fold
  12. Ventriculomegaly

V. Screening: Rating system to assess for Trisomy

  1. Scoring
    1. Nuchal Fold (5mm)
      1. Assess at level of Cerebellum and cisterna magna
      2. Not predictive after 21 weeks
      3. 2 Points
    2. Short femur length
      1. 1 Point
    3. Cystic Hygroma
      1. Seen in Turners Syndrome, Trisomy 21, Idiopathic
      2. 1 Point
    4. Septal defect or other heart defect
      1. 1 Point
    5. Choroid plexus cyst
      1. 1 Point
  2. Interpretation: Score associated with Trisomy risk
    1. Age <35: Score >= 2 points
    2. Age >35: Score >= 1 point

VI. Evaluation: Findings suggestive of Trisomy

  1. See Antenatal Screening
  2. See Aneuploidy Screening
  3. Consider Placental Cell-Free DNA
  4. Consider Amniocentesis with karyotype

VII. References

  1. LeFevre (2020) Am Fam Physician 101(8):481-8 [PubMed]

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