Trisomy 18 (Edwardssyndrome) is the second most common chromosomal trisomy after congenital dysmorphism. Also known as Edward’s syndrome, the abnormalities of trisomy 18 include mainly abnormalities of the mesoderm and its derivatives (e.g., skeletal, urogenital, and cardiac most notably). In addition, the ectoderm (e.g., skin folds, dermal crests, and hair) and endoderm (e.g., Merkel’s diverticulum, lungs, and kidneys), which are close to the mesoderm, are also abnormal. The literature reports normal development of the embryo until 5 weeks of gestation, with abnormalities beginning in the 6th to 8th week of gestation. Etiology The trisomy of chromosome 18 is due to chromosome non-separation during meiosis. The vast majority of cases are trisomy of the whole chromosome 18 in all cells, while a few are partial trisomy of chromosome 18 caused by chimerism and chromosome breakage heterotaxy. The child is characterized by posterior occipital protrusion, narrow forehead, small head, wide fontanelle, low ears with malformation, short eye fissures, small jaw, inner canthus, drooping eyelids, cleft lip or cleft palate. Short neck, excess skin on the neck, inguinal or umbilical hernia, tracheoesophageal fistula, biliary atresia. Horseshoe or ectopic kidney, double urethra, hydronephrosis and polycystic kidney. Hypoplastic external genitalia, hypospadias, cryptorchidism in males and large clitoris in females. The child has mental retardation, high muscle tone, hydrocephalus, bulging meninges, cerebellar hypoplasia, and corpus callosum hypoplasia. Hand clenched, thumb, index finger, middle finger tightly closed, index finger pressed on middle finger, pinky finger pressed on ring finger, pinky finger or all fingers only 1 transverse stripe, thumb hypoplasia or absence, through hand. Cradle foot, clubfoot, syndactyly, polydactyly, short sternum, limited hip abduction. Thyroid and adrenal hypoplasia, bicornuate uterus, coronary artery malformation, transposition of the great arteries, tetralogy of Fallot, etc. Diagnosis There is great variability in the clinical presentation of the disease, and no malformation is unique to trisomy 18. Therefore, the diagnosis cannot be made solely on the basis of clinical malformations, but must be confirmed by a cellular chromosomal examination, and the diagnosis is based on the results of karyotype analysis. Treatment Resuscitation is often required at birth. Low life skills, frequent apnea, poor sucking, and mostly nasal feeding are required. Despite careful care, most children die within the first 2 months and very few live to 1 year of age, all with severe mental retardation. Prevention In children with chromosomal translocations, the chromosomes of the parents should be examined to determine if one of them is a carrier of the balanced translocation. Such carriers have a higher chance of having children with this syndrome and require prenatal diagnosis.