I believe that some pregnant women have had the experience of being advised by their doctors to undergo amniocentesis because of the “high risk of Down’s syndrome screening” or “advanced age”, and I believe that many of them have chosen to give up because of the risk of amniocentesis. Those who choose to have amniocentesis are in a state of great anxiety before and after the procedure, and can be described as “mentally tortured”. It is a tormenting choice to choose to “wear” or “not to wear”. In fact, amniocentesis is only one of the invasive prenatal diagnostic techniques, in addition to chorionic villus aspiration and cord blood aspiration. Amniocentesis is the longest-standing, most widely used and safest invasive prenatal diagnostic technique, and has played an important role in diagnosing major fetal birth defects. So, “Which pregnant women need to undergo amniocentesis?” What is the best gestational age for amniocentesis?”, “What is the best gestational age for amniocentesis?” and “What are the risks of amniocentesis?” With these questions, let’s get to know amniocentesis during pregnancy in this issue. 1. Which pregnant women need amniocentesis? In fact, besides the “high risk of Down’s syndrome screening” and “advanced age” pregnant women mentioned above, there are many other situations that require amniocentesis. The common indications for amniocentesis include: ①Mother’s age at delivery ≥ 35 years; ②Prenatal screening for Down syndrome or trisomy 18 at high risk; ③Adverse maternal history: history of stillbirth or neonatal death, history of malformation or delivery of a child with mental retardation, history of delivery of a child with chromosomal abnormalities; ④Family history of genetic disorders, or history of delivery of a child with genetic disorders; ④History of delivery of a child with genetic disorders; and (4) family history of genetic diseases or history of delivery of children with genetic diseases; (5) chromosomal abnormalities of one of the spouses (such as balanced translocation or inversion); (6) carriers of genes for hereditary diseases; (7) fetal malformations or suspected malformations; (8) fetal paternity test. 2.How is amniocentesis done? Amniocentesis is the process of extracting amniotic fluid by passing an amniocentesis needle through the abdominal wall and uterine wall of the pregnant woman and then entering the amniotic cavity under the guidance of B ultrasound. The specific steps are: ① the pregnant woman is placed in a supine position, and a routine ultrasound examination is performed to estimate the fetal gestational age, observe the fetal heartbeat, heart rate and heart structure as well as other fetal anatomical structures, and determine the number of fetuses and the location of the placenta; ② select the puncture site, avoid the placenta as much as possible, and find the largest amniotic pool close to the abdominal wall for puncture; ③ after selecting the entry point, the skin of the abdomen is disinfected and sterile towels are laid; ④ under the real-time monitoring of ultrasound, the puncture needle enters the abdominal wall in turn. ④Under real-time ultrasound monitoring, the puncture needle enters the layers of the abdominal wall, the uterine wall and the amniotic cavity in turn, and the needle core is removed; ⑤Aspirate 2 ml of amniotic fluid with a 2 ml syringe and discard it. This section of amniotic fluid may contain maternal cells so as not to interfere with the subsequent examination. Then use a 20 ml syringe to aspirate 20 ml of amniotic fluid; ⑥ At the end of the procedure, withdraw the puncture needle and observe the fetal heartbeat and fetal movement with ultrasound again; ⑦ Apply a medical dressing after compressing the needle eye with sterile gauze for 2 to 3 minutes. After 2 hours of rest and observation outside the clinic, the pregnant woman can go home if there are no adverse reactions and try to avoid long distance work. The whole process of amniocentesis takes about 5 to 10 minutes. The doctor will operate to minimize the impact on the fetus and reduce the risk of fetal damage. Since the amniocentesis is performed under real-time ultrasound guidance, mothers and fathers-to-be do not have to worry about the puncture injuring the fetus. Sometimes we encounter situations where the entire anterior wall of the pregnant woman’s uterus is placenta, and the doctor will also use surgical techniques to quickly cross the placenta to reduce bleeding. 3. What is the best week of pregnancy for amniocentesis? Based on our many years of experience, we recommend that amniocentesis should ideally be performed between 18 and 22 weeks of gestation. The total amount of amniotic fluid in this trimester is estimated to be more than 500-600 ml, and the extraction of 20 ml of amniotic fluid will not have much effect on the entire amniotic pool. In addition, the amniotic cavity is relatively large at this time, making it less likely that the fetus will be stabbed when the amniotic fluid is extracted by needle puncture. Most importantly, the proportion of live cells in amniotic fluid during this period is about 20%, which is conducive to amniotic fluid live cell culture and chromosome preparation. As gestational age increases, the fetal epidermal cells will keratinize, and the success rate of extracting these keratinized cells for culture will be greatly reduced. 4.What can be checked in fetal amniotic fluid? In practice, fetal chromosome karyotyping is the most important purpose of amniotic fluid extraction. Simply put, the 46 chromosomes of the fetus are sequentially sorted and analyzed for quantitative abnormalities and obvious structural abnormalities. For example, if the analysis reveals that the fetus has 3 chromosome 21, the fetus can be diagnosed with Down’s syndrome; another important role is to perform fetal genetic diagnosis, such as thalassemia, congenital deafness, phenylketonuria, progressive muscular dystrophy, albinism and hemophilia; we apply gene chips to also check some specific chromosome microdeletion or microduplication syndromes, which can be used to diagnose some Amniotic fluid can also be used to detect intrauterine infections such as rubella virus, cytomegalovirus and toxoplasmosis; amniotic fluid can also be used to detect certain genetic metabolic diseases, such as the detection of certain enzymes or metabolic substances in amniotic fluid to predict the risk of fetal disease. Many mothers and fathers-to-be think that an amniocentesis test will ensure that the fetus is completely normal, but in fact, amniocentesis does not detect all diseases and we need to be rational about the role of amniocentesis. Left: Normal female karyotype; Right: Female karyotype with trisomy 21 5. What are the risks of amniocentesis? Amniocentesis is an invasive test, so there are certain risks associated with the procedure. Pregnant women may be at risk of bleeding, placental hematoma, amniotic fluid spillage, amniotic fluid embolism, and other complications of the procedure. In addition, there is a possibility of intrauterine infection, fetal injury, puncture failure or amniotic fluid cell culture failure, but the probability is very low. 6. Does amniocentesis hurt? In addition to the risk of miscarriage, the pain of puncture may be the second concern of pregnant women. Amniocentesis is performed without the aid of anesthesia, which may cause some pregnant women to experience a slight stimulation of the abdomen and a varying degree of sensation, such as urgency or pressure. Most pregnant women will feel mild pain during the puncture, which is tolerable. Some other pregnant women may not feel any discomfort. 7.Can a pregnant woman with an infectious disease have an amniocentesis? Currently, the common infectious diseases include hepatitis B, syphilis and AIDS. If a pregnant woman is only a carrier of hepatitis B virus (normal liver function, HBV-DNA copy <500), she can undergo amniocentesis for prenatal diagnosis. If the pregnant woman is HBe antigen positive and the HBV-DNA copy size is ≥500, in principle, it is a contraindication to the puncture procedure, so we need to weigh the pros and cons of amniocentesis in relation to the maternal risk. For syphilis and AIDS, according to current industry and international practice, puncture operations should be reduced or avoided during active syphilis and interventional puncture procedures should be avoided for AIDS. In practice, we generally need to fully communicate with pregnant women and their families after weighing the pros and cons of the puncture procedure, and ultimately decide whether to perform it. 8. Can non-invasive DNA testing replace amniocentesis? The answer is no. In terms of the current level of development of non-invasive DAN testing technology, it is mainly used to detect the risk of fetal trisomy 21, trisomy 18 and trisomy 13, but it may miss 30% of chromosomal abnormalities, and has great limitations for the diagnosis of chromosomal structural abnormalities and monogenic genetic diseases. Therefore, non-invasive DNA testing is currently only a screening technique with high accuracy, not a diagnostic technique, and therefore cannot replace amniocentesis prenatal diagnostic testing yet. Some doctors without professional genetic counseling training often confuse non-invasive DNA testing with amniocentesis prenatal diagnosis, exaggerate the risks of amniocentesis, and irresponsibly induce pregnant women to choose non-invasive DNA testing, which is very irresponsible. Friends, amniocentesis, as one of the secondary prevention tools for birth defects, plays an important role in the diagnosis of fetal chromosomal disorders, monogenic genetic disorders and genetic metabolic diseases. Due to the limited space, we do not have a detailed introduction of pre and post amniocentesis precautions and contraindications to the puncture procedure. We suggest that pregnant women with prenatal diagnosis indications must go to a professional prenatal diagnosis institution for consultation and not to miss the best week of pregnancy for the puncture.