which one of the following congenital malformation of the fetus can be diagnosed in first trimester by ultrasound :

Anencephaly is defined as absence of the cranial vault and is incompatible with life.This was the first anomaly to be detected on USG and pregnancy to be terminated.It is usually diagnosed by 12 weeks (first trimester)of pregnancy on USG.There is a typical frog's eye apperanace on USG. Refer page no 487 of Text book of obstetrics,sheila balakrishnan 2nd edition.