Example 1 Down’s syndrome In outpatient clinics, we often encounter some pregnant women who take the initiative to request fetal karyotyping after pregnancy, and after consultation, we learn that these pregnant women have given birth to children with trisomy 21, and many of them are highly educated and highly qualified couples. A 35-year-old pregnant woman in a tertiary A-class hospital regular perinatal health care, Down’s disease screening results for low-risk, did not carry out fetal chromosome analysis, unfortunately, the child was born with “trisomy 21 face, through the palm,” the karyotype was diagnosed as “trisomy 21 child The karyotype confirmed the diagnosis of “child with trisomy 21”. In addition, some pregnant women do not understand the amniotic fluid extraction technique very well, always think that the risk is high, and both parties do not have a family history of hereditary disease, or have already given birth to a healthy child, thinking that there is no need for further diagnosis, and miss the best time for diagnosis and ultimately lead to misfortunes. Therefore, prenatal diagnosis is necessary for all pregnant women of advanced age, and pregnant women who conceive with the help of in vitro fertilization techniques are no exception. Example 2 Duchenne muscular dystrophy (DMD) is an X-chromosome-linked recessive disorder with a severe risk of 1 in 3500 live births to male infants. The disease is caused by mutations in the dystrophin gene that result in structural and functional changes in the skeletal proteins of the myocyte membrane.Patients with DMD often develop the disease around the age of 5 years and die of severe comorbidities around the age of 20 years. There is no effective treatment for this disease. A couple was seen in the outpatient clinic with the female’s brother and 2 uncles as patients. She was currently 4 months pregnant with an ultrasound suggestive of a boy, and the family was very concerned about the fetus as a patient. The female was confirmed to be a carrier of the disease-causing gene by family chain analysis. DNA was extracted from the amniotic fluid specimen and deletion analysis and chain analysis were performed, confirming that the X chromosome of the male fetus was of maternal grandparent origin, and that the disease-causing X chromosome had not been acquired, and the fetus was confirmed to be normal by postnatal follow-up. Currently, six cases of affected children have been identified and recommended for induction of labor at our institute. Example 3 Progressive proximal spinal muscular atrophy (SMA) is a relatively common chromosomal recessive disorder characterized by progressive muscle weakness and myasthenia gravis. The causative gene carrier is 1/50 in the population, and the survival motor neuron (SMN) gene located on chromosome 5 is the determinant gene for spinal muscular atrophy, and 90-98% of patients with SMA have a deletion of the SMN1 gene. A consanguineous couple who had three consecutive children with SMA, two of whom had died, came to the clinic with their third child, who was unable to walk, and was found to have a pure and homozygous deletion of exons 7 and 8 of the SMN1 gene, which supported the diagnosis of SMA. The wife came for prenatal diagnosis at 18 weeks’ gestation and the fetus was confirmed to be a normal female. Because of the high probability of carriers of the SMA-causing gene in the population, relatives of couples who give birth to a child with SMA may still give birth to a child with the disease. Therefore, the trend of detecting carriers in the population and avoiding the birth of affected children will be the development of the prenatal diagnosis of SMA disease. Example 4 Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common single-gene genetic diseases in humans, with a prevalence of 1/800, and about 85% to 90% of patients are caused by mutations in the PKD1 gene, with the rest associated with PKD2 and PKD3. There is no effective treatment for this disease and it is late dominant, which is not conducive to pre-symptomatic diagnosis and prevention. In the outpatient clinic, a man complained of autosomal dominant adult polycystic kidneys in both his mother and uncle. At the age of 28, he found out that he had the same disease as his mother during a physical examination at his workplace, and his mother was already critically ill due to renal failure. The man’s wife was in her fourth month of pregnancy and requested prenatal diagnosis of the fetus in order to avoid fetal disease. Prenatal preanalysis showed that the family line was due to a mutation in the PKD1 gene, and the prenatal diagnosis supported the acquisition of the disease-causing chromosome by the fetus, and the woman decided to induce labor. Prenatal diagnosis is a great progress of modern medicine, with the increasing improvement of fetal specimen sampling technology, molecular diagnostic technology and imaging technology, prenatal diagnosis will have a broader space for development.