Definition:

Edwards syndrome, also known as trisomy 18, is a chromosomal disorder due to the presence of an extra chromosome 18, either full, mosaic trisomy, or partial trisomy 18q. This disease is the second-most common autosomal trisomy, after Down syndrome. The live born prevalence is estimated as 1/6,000-1/8,000, but the overall prevalence is higher (1/2500-1/2600) due to the high frequency of fetal loss and pregnancy termination after prenatal diagnosis. The main clinical features include prenatal growth deficiency, characteristic craniofacial features, distinctive hand posture, nail hypoplasia, short hallux, short sternum, and major malformations (particularly involving the heart). Approximately 50% of newborns survive beyond 1 week while more than 90% do not survive beyond 1 years of age.