When a pregnant woman has a chromosomal abnormality, the abnormal chromosome may be passed on to the fetus, and the presence of abnormal chromosomes in the fetus may cause malformations. If a woman has abnormal chromosome 18 or 21, it is clinically known as trisomy 18 or trisomy 21, and the fetus is prone to Down’s syndrome, lower intelligence than normal children, short stature and facial deformities. It is recommended that pregnant women with chromosomal abnormalities go to the hospital for appropriate tests, mainly amniocentesis, to determine whether the fetus has abnormal chromosomes and then decide whether to continue the pregnancy. Pregnant women can take folic acid under the guidance of a doctor during the first trimester to prevent fetal malformations.