The incidence of this disease in newborn infants is 1:3500-8000, mostly occurring in older parents, 52% over 35 years of age. The incidence is higher in girls than in boys, about 3 to 4:1. The incidence is higher in mothers who conceive in autumn and winter, and increases with the age of the parents at the time of birth. The average age of the mother is 32.5 years, with two peaks at 25-30 and 40-45 years, and the average age of the father is 34.9 years. In a few patients, the age of both parents is not relevant. The mothers are on average 42 weeks of gestation and often have a late delivery. Moreover, the mothers feel weak fetal movements during pregnancy, have a lot of amniotic fluid, a small placenta and often only one umbilical artery. The malformations 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) close to the mesoderm are also abnormal. The literature reports normal development of the embryo before 5 weeks, with abnormalities beginning in the 6th to 8th week of gestation. 1. Growth and development Body weight at birth is relatively low compared to the mother’s gestation time, averaging about 2240 g. Mental and motor development is delayed, the body is small, breastfeeding is difficult, response to sound is weak, and skeletal and muscular development is poor. The muscle tone is initially hypotonic and later increases. 2, most deformities (1) craniofacial: long anterior and posterior head diameter, small head circumference, protruding occipital bone. Both eyes and eyebrow distance are widened, both sides of the inner canthus, cloudy cornea, drooping eyelids, and small eye deformity are common. The nasal bridge is elongated and elevated, and the nostrils are often turned upward. The mouth is small, the palatal arch is high and narrow, and the lower jaw is small. The ears have distinctive features: low ear position, flat auricle, and pointed upper part. In addition, occasional deformities such as meningeal bulge, cleft lip, cleft palate, posterior nostril atresia and external auditory canal atresia are seen. (2) Thorax: The neck is short and the cervical skin is excessively long and webbed. More than 95% of cases have cardiac malformations, such as ventricular septal defect and arteriovenous ductus arteriosus, while atrial septal defect is rare, and aortic or pulmonary artery diastasis, aortic constriction, tetralogy of Fallot, aortic span, right-sided heart, and right-sided aortic arch. These cardiovascular malformations are often the cause of death. Esophagotracheal fistulae may also be present. The right lung is abnormally segmented or absent. (3) Abdomen: abdominal muscle defects are mostly seen in umbilical hernia, inguinal hernia, and separation of the rectus abdominis muscle. Pyloric stenosis, diaphragmatic hernia, and Meckel’s diverticulum are also more common. Pancreatic or splenic heterotopia, intestinal dysplasia, cholelithiasis, gallbladder dysplasia, etc. are also seen. Renal malformations include polycystic kidney, ectopic kidney and horseshoe kidney, hydronephrosis, giant ureter and double ureter, especially horseshoe kidney, heavy kidney and double ureter. Pelvic stenosis is more common. (4) Extremities: The posture of the hand is characteristic of trisomy 18: the fingers are flexed, the thumb, middle finger and index finger are tightly closed, the index finger is pressed on the middle finger, the little finger is pressed on the ring finger, the fingers are not easily straightened, if they are passively straightened, the middle finger and little finger are slanted to the ulnar side, the thumb and index finger are to the flexor side, the index finger and middle finger are separated, forming a “V” shape. Hypoplastic nails. The child often raises both hands along the side of the head. The index and middle fingers often have parallel and multiple fingers. The fifth metacarpal bone is short. The bunions are short and dorsiflexed. Thigh abduction is limited due to increased muscle tone. There is congenital hip dislocation. The heel bone is prominent and has a rocking chair-shaped foot. Horseshoe clubfoot may be seen. In addition, short limb deformity (Phocomilia) is occasionally seen. (5) Genitalia: 1/3 of boys have cryptorchidism, 1/10 of girls have clitoris and labia majora hypoplasia, and perineal anomalies and anal atresia are often seen. Ovarian hypoplasia, bicornuate uterus and scrotal division are rare. (6) Endocrine system: There may be thyroid hypoplasia, thymus hypoplasia, and exceptionally small adrenal glands of approximately 2 g. (7) Skin and dermatoglyphic features: The skin has many fine hairs, folds, and appears angiomatous. Fingerprint features include more than six bowed lines, only one transverse line in the fifth finger, and 30% have a through hand (or ape line) as well as an axial three shot distal position in t′ or t″. The disease is not easily survivable. The literature reports that about 30% survive to 3 months of age, less than 10% survive to 1 year of age, and only 1 to 2% survive to 10 years of age. Those without congenital heart disease generally have a longer survival time. Those who survive beyond infancy are almost always girls.