This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Antenatal Care & Assessment of Fetal Well Being, Subject name: Gynaecology & Obstetrics
[{'content': 'Which Congenital malformation of the fetus can be diagnosed in first trimester by ultrasound? \nSelect and explain. \nA. Anencephaly, B. Iniencephaly, C. Microcephaly, D. Holoprosencephaly', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. A. AnencephalyUltrasound can be used to detect anencephaly as early as 10 weeks' gestation. With an abnormal head/trunk ratio and abnormally large orbits, the absence of the superior vault is associated.The length of crown-rump is normal in most anencephalic fetuses.", 'role': 'assistant'}]