Which one of the following congenital malformations of the fetus can be diagnosed earliest in a first trimester ultrasound?

Anencephaly can be reliably diagnosed at 11-14 weeks of gestation by ultrasound scan. With careful imaging it can be diagnosed even as early as the 8th or the 9th week. The most impoant feature is the absence of calvaria above the bony orbits paicularly on taking a coronal image of the face. It has little or no cerebral tissue usually, although some tissue might be seen protruding from the defect. The crown-rump length is reduced significantly. The ultrasonogrm shows a typical mickey mouse face sign on taking a coronal section of the head. Ref: Diagnostic imaging of fetal anomalies By David A. Nyberg, John P. McGahan, Pages 293-296, 275-276, 306-309, 232-235; The Spina Bifida: Management and Outcome By M. Memet Ozek, Giuseppe Cinalli, Wirginia June Maixner, Pages 75-81; Prenatal Diagnosis and Therapy By Chakravay, Page 74.