This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics of Common Disorders, Subject name: Pediatrics
First trimester USG finding in Down syndrome- 
Select and explain. 
A. Nuchal thickening, B. Nuchal translucency, C. Cardiac anomalies, D. GI anomalies
B: Nuchal translucency
Answer: B: Nuchal translucency 
Explanation: Ans. is 'b' i.e., Nuchal translucency Maternal serum screeningo 1st trimesterMaternal beta hCGo Higher than chromosomal ly normal fetuseso Difference increases with gestationPAPP-Ao Lower than chromosomally normal fetuseso Difference decreases with gestation: therefore not commonly used as a second-trimester testo 2nd trimesterTriple screeningMaternal free beta hCG: higher than chromosomally normal fetusesAFP: lower than chromosomally normal fetusesUnconjugated oestriol (uE3): lower than chromosomally normal fetusesUltrasoundo First trimesterNuchal translucency: thickness depends on the size of the fetus (CRL), but in general it is considered abnormal if >3 mm.There is recent evidence thai the inclusion of nasal bone measurement improves the specificity of 1st trimester datao Second trimesterApproximately 30% of babies with Down syndrome have detectable abnormalities on the mid-trimester ultrasound 1.