Both trisomy 18 and high risk of trisomy 21 are severe, with trisomy 18 being a bit more severe in comparison. Trisomy 18 has a high miscarriage rate, and even when born, more than 90% of children die within one year of age, with only a very small percentage of patients surviving into childhood. With improved medical care, many patients with trisomy 21 live into adulthood. Therefore, it is a bit more serious to consider the high risk of trisomy 18. Trisomy 18 and Trisomy 21 are both autosomal genetic disorders, and patients generally have more severe or significant congenital multiple malformations, intellectual or growth retardation. It is therefore particularly important to carry out preconception testing and screening during pregnancy to prevent and reduce the number of children born with these conditions.