Phenylketonuria can be screened prenatally before the birth of a newborn. The procedure involves genetic screening using amniotic fluid drawn through amniocentesis between the 16th and 20th week of pregnancy. Phenylketonuria is an autosomal recessive hereditary disease, greatly associated with chromosomal abnormalities. If chromosomal abnormalities are detected through amniocentesis, indicating the presence of pathogenic genes, it confirms that the fetus will be born with phenylketonuria. If both parents carry the relevant genes, prenatal screening is still necessary to rule out the risk of the disease in the fetus.