This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetic Approach to Pediatric Medicine, Subject name: Pediatrics
The earliest congenital anomaly identified by ultrasound is: 
Select and explain. 
A. Hydrocephalus, B. Encephalocele, C. Spina bifida, D. Anencephaly
D: Anencephaly
Answer: D: Anencephaly 
Explanation: Ans. (d) AnencephalyRef.: Nelson 18th ed./Ch. 592.6* Anencephaly is absence of cranial vault posteriorly with brain and meninges exposed.This condition can be detected by antenatal USG as early as 11-12 weeks.