Trisomy 18 is caused by an individual with an extra chromosome 18 and was first reported by Edwards in 1960, also known as Edwards syndrome. The main mechanism of trisomy 18 is the non-disjunction of chromosome 18 during germ cell meiosis. The main mechanism of trisomy 18 is the non-segregation of chromosome 18 during the meiosis of germ cells, more than 90% of which originate from the maternal side, and the non-segregation occurs mostly during meiosis II of the egg and is related to maternal age. The clinical manifestations of patients include severe mental retardation, developmental delay, increased myotonia in the neonatal period, and multiple organ malformations. 90% of patients have cardiac malformations, with ventricular septal defect being the most common, and others include atrial septal defect and patent ductus arteriosus. 43% have craniofacial malformations, including occipital protrusion, cleft lip and palate, short mandible, choroidal cyst, etc. 40% have horseshoe kidney, and gastrointestinal malformations appear In 40% of cases, in addition to the characteristic fist-like shape of the hands, short bunions, protruding heels, clubfoot, single umbilical artery, diaphragmatic hernia, and umbilical bulge. Prenatal diagnosis] Trisomy 18 often has characteristic ultrasound signs, including strawberry head, choroidal cysts, fist-like fingers, etc. Excessive or low amniotic fluid and intrauterine growth retardation are frequent concomitant phenomena, and definitive diagnosis requires amniotic fluid or chorionic villus chromosome examination. The risk of recurrence of trisomy 18 is very low, but for pregnant women over 35 years old, they should be informed of the risk of recurrence of the next pregnancy. The risk of recurrence of trisomy 18 is low, but for pregnant women over 35 years of age, they should be informed of the risk of other chromosomal aneuploidy in the next pregnancy, and prenatal diagnosis should be performed as early as possible in the second pregnancy.