Every family with a history of genetic disorders aspires to be free from genetic disorders. With the advancement of assisted reproduction technology, especially the application of pre-implantation genetic diagnosis technology, embryos carrying genetic mutations are genetically identified and blockage of genetic diseases is achieved at the embryonic level. The third generation IVF technology has strict indications, mainly to help parents avoid a certain genetic disease with a clear cause and have a baby without the disease. Clinically, PGD can be done for chromosomal number and structure abnormalities, monogenic genetic disorders, sex-linked genetic disorders, mitochondrial disorders, etc. CAH, as an autosomal recessive monogenic disorder, fits the indications for PGD. Congenital adrenocortical hyperplasia (CAH) is a group of autosomal recessive disorders caused by defects in the enzymes involved in the synthesis of adrenocortical hormones, also known as adrenogenital syndrome or adrenal metaplasia. It is mainly due to defects in enzymes necessary for adrenocortical hormone biosynthesis, resulting in abnormal corticosteroid synthesis. In most cases, the adrenal glands do not secrete enough glucocorticoids and salt hormones but too many androgens, so there are different degrees of hypoadrenocorticism, accompanied by masculinization in girls and precocious puberty in boys. Clinical manifestations: The clinical manifestations of this disease depend on the site of enzyme deficiency and the severity of the deficiency, and the following types are common: 1) 21-hydroxylase deficiency; 2) 11-β-hydroxylase deficiency; 3) 3β-hydroxysteroid dehydrogenase deficiency; 4) 17-hydroxylase deficiency. Among them, 21-hydroxylase deficiency is the most common, accounting for 90-95% of the disease. Identification of the different types relies on hormone level measurements and genotype analysis. The incidence of typical CAH is about 10/100,000, whereas the incidence of atypical is about 10 times higher than typical and is race-specific. If both couples carry genes for CAH-related genetic disorders, there is a chance that the baby conceived in IVF will be a sick baby and a difficult life awaits him. With third generation IVF (PGD) technology, the embryos can be “checked” before they are implanted in the mother’s womb, and the “healthy” ones or the carriers (i.e. heterozygotes) can be selected for implantation in the mother’s womb, thus avoiding the birth of a sick baby. The third generation IVF technique involves taking 5-8 cells of the embryo for genetic analysis to diagnose any abnormalities before transfer, freezing the blastocyst first, and then thawing the embryo for transfer after screening for healthy embryos. At present, there are still very few medical institutions in China that are allowed to perform “third generation IVF” technology.