Birth defects, also known as congenital anomalies, refer to the abnormalities in morphology, structure, function, metabolism, behavior and other aspects caused by the disorder of baby’s development in the mother’s womb before birth, which can be caused by genetic and environmental factors. There are four common types: ① congenital malformation; ② Hereditary metabolic diseases; ③ Congenital disability; 4 mental retardation. China is a populous country in the world, and the incidence of defective infants is about 5.6%, which is an important cause of early abortion, stillbirth, congenital disability, perinatal and infant death.
Three-level prevention and control of birth defects is a comprehensive prevention and control system covering pre-pregnancy, pregnancy and postpartum stages. Prenatal screening and prenatal diagnosis belong to the category of secondary prevention of birth defects. Its purpose is to minimize the birth of newborns with serious defects such as severe illness, severe disability or fatal diseases. They make up for the primary prevention and further prevent and control the tertiary prevention, and play an important role in the birth defect prevention and control system.
I believe pregnant mothers have heard the names of "prenatal screening" and "prenatal diagnosis" many times. What are prenatal screening and prenatal diagnosis? What is the difference between the two? Let Xiaobian give you one together. ……
First, about prenatal screening
To put it simply, prenatal screening mainly uses some basic and simple methods to screen the fetus for birth defects and malformations, such as serological screening and medical image screening, so as to judge the probability of the fetus suffering from some birth defects or genetic diseases such as Down syndrome and open neural tube defects. Commonly used screening methods include:
(1) Down syndrome screening technology. Down’s syndrome screening technology is the most widely used prenatal screening method in clinic at present. It detects the concentrations of alpha-fetoprotein (AFP), chorionic gonadotropin (HCG) and free estriol (FE3) in maternal blood by extracting the peripheral blood of pregnant women at 15-20+6 weeks of pregnancy, and calculates the detection method of fetal risk coefficient with birth defects in combination with the gestational age, weight and age of pregnant women. The detection method is mainly aimed at the risk assessment of Down syndrome (trisomy 21), trisomy 18 syndrome and congenital neural tube defects. The detection method has the advantages of fast detection speed and low cost, but the false negative and false positive rates of this method are high, and the method fails to cover all the population, and there are many factors that affect the results (including the age and weight of pregnant women, diabetes, medication during pregnancy, etc.). Only the risks of Down syndrome, trisomy 18 syndrome and neural tube defects are predicted, and the number and structure of other chromosomes cannot give specific risk values, so there are strict requirements for pregnant women’s gestational age. The emphasis is on screening, and the screening results generally show low risk, critical risk and high risk. Screening out high risk does not mean that there must be some diseases in the fetus, and it needs to be further diagnosed by prenatal diagnosis technology.
(2) Non-invasive prenatal screening technology. That is to say, we often say that the detection of fetal free DNA in maternal peripheral blood is more sensitive and specific than screening for Down syndrome. Routine non-invasive three methods can screen 13- trisomy, 18- trisomy and 21- trisomy, while non-invasive PLUS developed in some hospitals can screen nearly 100 kinds of fetal chromosomal abnormalities. However, this technology still belongs to prenatal screening and its cost is high, so it can’t detect fetal congenital neural tube defects. If the test result is high risk, further prenatal diagnosis is needed to confirm the diagnosis. The advantage of this test project is that it can be tested after 12 weeks of pregnancy, and only 10 ml of venous blood of pregnant women is needed, and the results can be obtained in a few days. Because this method is non-invasive and painless, it can avoid the risk of abortion and infection caused by amniocentesis. However, it is not perfect. The disadvantages of this technology are: First, it can’t detect twins or multiple births, because it can’t judge which fetus the free DNA in pregnant women’s blood comes from; Second, if the mother’s own chromosome has problems, such as aneuploidy or chimera, then this technique is also not applicable; Third, if the pregnant woman has recently received allogeneic blood transfusion, the foreign DNA will interfere with the analysis results, and it is not suitable for this technology.
(3) Prenatal ultrasonic structure screening technology. At present, B-ultrasound examination is commonly used in clinic, which is the most widely used examination method in obstetrics. It is mainly used in: ① it can directly monitor the growth and development of the fetus and observe whether there are morphological abnormalities in the fetus, such as fetal neural tube development defects, skull abnormalities, visceral malformations, etc.; ② Confirm the gestational age, and calculate the risk of Down’s syndrome (DS) by risk calculation software, combining with serological screening markers; ③ Used to mediate chorionic sampling, amniocentesis and umbilical cord puncture; ④ The nuchal translucency (NT) and nuchal fold (NF) of fetus were detected. NT and NF are the most commonly used and effective indicators for ultrasound screening of Down syndrome. NT detection is mostly in the first trimester (10 ~ 14 weeks of pregnancy). When the thickness of transparent layer of fetal neck is more than 3 mm, DS high-risk pregnancy is considered. NF is mainly used for screening in the second trimester (16-24 weeks of pregnancy). When the fetal NF thickness is greater than or equal to 5 mm at 16-18 weeks of pregnancy, and the fetal NF thickness is greater than or equal to 6 mm at 19-24 weeks of pregnancy, it is considered as a DS high-risk pregnancy. Therefore, ultrasound, as a non-invasive examination method, has always played an important role in prenatal screening. It can not only detect fetal development, but also detect some serious fetal malformations and pregnancy complications. If abnormalities are found, further prenatal diagnosis and testing are needed.
Second, about prenatal diagnosis
Prenatal diagnosis refers to the detection and diagnosis of the development status and diseases of the embryo or fetus through certain methods before birth, which is the key link to prevent birth defects.
Prenatal diagnosis is based on prenatal screening or aimed at high-risk pregnant women. Therefore, prenatal diagnosis can be used to further diagnose the disease. Karyotype analysis of amniotic fluid (chorionic villus or umbilical cord blood) cell culture is a traditional method, which is called the "gold standard" for prenatal diagnosis.
So what is chromosome karyotype analysis?
Fetal karyotype is mainly based on the development of amniocentesis, chorionic villus biopsy and umbilical vein puncture technology, and the analysis of fetal karyotype has become the most widely used technology for prenatal diagnosis. This technique has high diagnostic accuracy and high reliability in clinic, so it is the gold standard for prenatal diagnosis.
It is necessary to remind expectant mothers that although prenatal diagnosis technology in China has developed by leaps and bounds, cytogenetics technology, molecular biology technology and gene sequencing technology have continued to develop, at present, all technologies still have their limitations, and prenatal diagnosis technology cannot detect all fetal abnormalities.
Original title: "Two Screens" Policy Knowledge Publicity on People’s Livelihood (II)-Prenatal Screening and Prenatal Diagnosis "
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