This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiology Q Bank, Subject name: Radiology
A 34 years old patient came for antenatal ultrasound in her 2nd trimester. Her beta HCG level is raised, however AFP level is decreased. Patient has one 5 years old child who does not have any chromosomal abnormalities. Most likely diagnosis is? 
Select and explain. 
A. Down syndrome, B. Patau syndrome, C. Edward syndrome, D. Trisomy 16
A: Down syndrome
Answer: A: Down syndrome 
Explanation: Quadruple Screening test On mother's serum at 16 weeks of gestation Evaluation Trisomy NTD Omphalocele Gastroschisis Multiple Gestatoin 21 18 13 AFP | | | | uE3 | | NA NA HCG | | NA NA DIA | | NA NA Above ultrasound image shows VSD which can be seen in trisomy 21.