Prenatal diagnosis, also known as intrauterine diagnosis, is an accurate diagnosis of whether the embryo or fetus has a certain genetic disease or congenital malformation before birth. The principles for selecting the indications for prenatal diagnosis are, first, high-risk and more harmful genetic diseases; second, the means for prenatal diagnosis of the disease are available. Several major prenatal diagnostic methods are as follows: 1. X-ray examination is mainly used to check for congenital malformations of the fetal skeleton before 18 weeks. However, because X-rays have certain effects on the fetus, they are rarely used now. B-type ultrasound is the most widely used and can be used for prenatal diagnosis or exclusion diagnosis. In addition, direct dynamic observation of fetal heartbeat and fetal movement, and video recording and analysis can also be used for placental positioning, selection of amniocentesis site, guided fetoscopy operation, collection of chorionic villi and umbilical cord blood specimens for laboratory examination. Fetoscopy, also known as amnioscopy or hysteroscopy, is a double-cannula fiberoptic endoscope with amniocentesis. It can directly observe the fetus and can be operated from 15-21 weeks of pregnancy. It is mainly used for fetal blood sampling, biopsy and prenatal diagnosis. More than 8 hereditary skin diseases can be diagnosed using skin biopsy, and fetal morphological abnormalities can also be observed. In addition, fetoscopy can determine the sex of the fetus and provide intrauterine treatment for certain genetic diseases. Due to the application of B ultrasound, this method has been used less frequently. 4, amniocentesis The best time to extract amniotic fluid is 16-20 weeks of pregnancy. Because of the large amount of amniotic fluid and floating fetus at this time, it is easy to enter the needle when puncturing, and it is not easy to hurt the fetus. The fetal cells in the amniotic fluid can be cultured in vitro for chromosome analysis, enzyme and protein testing, and sex chromatin examination to extract DNA for genetic analysis, or without culture, using microtechnology for enzyme and protein analysis or direct DNA extraction for genetic diagnosis. 5. Villi aspiration Villi can be sampled through the cervical area, preferably under ultrasound surveillance. It is usually performed at 9-11 weeks of gestation. The chorionic villus branches are processed (strictly separated from the meconium) or cultured for a short period of time for chromosomal analysis, enzyme and protein detection and direct DNA extraction for genetic analysis. 6.Cordocentesis The extraction of fetal venous blood through the mother’s abdomen can be performed under ultrasound guidance in the middle and late pregnancy (17-32 weeks). This technique has become far more popular in China than abroad and has a high success rate and is also safer. Umbilical cord blood can be used for various chromosomal or hematological tests and also for diseases that cannot be diagnosed by DNA analysis due to failure of amniotic fluid cell culture and can be tested biochemically with fetal plasma or blood cells, or when the timing of chorionic villus and amniotic fluid sampling is missed, and in some cases, instead of genetic analysis. For example, Hb Barts can be directly determined for alpha geodystrophy; coagulation factor VIII can be directly determined for hemophilia. 7. Pre-implantation diagnosis Pre-implantation testing of blastocysts using micromanipulation techniques and DNA amplification. The main methods to obtain preimplantation embryos are: uterine flushing and in vitro fertilization. The basic techniques for preimplantation diagnosis include: (i) microbiopsy of the oocyte: i.e., isolation of individual cells from embryonic cells at the 2-8 cell stage for testing; (ii) freezing and storage of embryos: if the microbiopsy technique is rapid, they can be returned to the uterus without freezing; and (iii) culture of the oocyte: the aim is to obtain more cells to facilitate diagnosis. Although there are only a few successful precedents and the operation is difficult and not yet available for clinical use, the prospects are attractive.