Earliest detectable congenital malformation by USG is :

Ans is a i.e. anencephaly As discussed in chapter on fetal malformation, anencephaly can be diagnosed as early as 8-10 weeks / first trimester in experienced hards. Microcephaly It is decreased head size. In these patients both brain mass and total cell number are reduced. There is dispropoion in size between the skull and face. It is difficult to recognize this anomaly by ultrasound -- A head circumference below 2 SD from the mean is used as a diagnostic criteria in midtrimester scan. Holoprosencephaly is the presence of a single centrally placed cerebral ventricle and may be associated with midline abnormalities of the face. With the use of vaginal probe it can be recognised in the beginning of midtrimester. Also Know Encephalocele can also be recognised in first trimester and is seen as a bony defect with protrusion of the brain tissue and meninges. Occipital encephaloceles are commonest. A genetic association of encephalocele and polycystic kidney and is called Meckel-Gruber syndrome. which is an autosomal recessive disorder.