On a second-trimester anomaly scan, the nuchal fold measured at the level of the cavum septi pellucidi and thalami is 8 mm at 19 weeks. This finding is most strongly associated with:
- A Trisomy 18
- B Trisomy 21 ✓
- C Spina bifida
- D Congenital diaphragmatic hernia
Correct answer: B. Trisomy 21
Explanation
The nuchal fold, measured from the outer edge of the occipital bone to the outer skin surface between 15 and 20 weeks, is considered thickened when it exceeds 6 mm. It is one of the strongest second-trimester soft markers for trisomy 21 and warrants offering invasive karyotyping when isolated. Spina bifida presents with cranial signs such as the lemon and banana signs rather than a thickened nuchal fold, and trisomy 18 is classically linked to choroid plexus cysts and clenched fists.
Reference: Callen's Ultrasonography in Obstetrics and Gynecology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.