Down's syndrome (DS) and neural tube defects (NTD) prenatal screening method Dr. Wu Yuping, School of Life Sciences, Zhongshan University, Zhuhai Ai Boluo Biotechnology Co., Ltd. Zheng Weijing, deputy director of pharmacist I. Prenatal screening: 1. What is screening: Screening is a systematic approach to identifying high-risk individuals for a particular disease from those who are asymptomatic and not receiving medical attention by means of testing or interrogation, and further tracking or taking direct Precaution. 2. What is prenatal screening: Prenatal screening is a screening of the “dangerous†extent of a pregnant woman with certain congenital abnormalities. The purpose of prenatal screening is to further diagnose the high-risk population and provide pregnant women with methods to terminate the pregnancy to prevent and reduce birth defects. The two main diseases currently screened for prenatal screening are Down's Sydrome (also known as Trisomy 21) and Open Neural Tube Defect (ONDT). Prenatal screening can be performed early in pregnancy (7-13 weeks) or in the middle (14-21 weeks). According to current technical limitations, prenatal screening techniques are not 100% correct, and false negatives (missing a disease pregnancy as a normal pregnancy) and false positives (a normal pregnancy as a disease pregnancy) can occur. False-negative cases are therefore misdiagnosed, and false-positive cases are generally corrected during prenatal diagnostic tests.
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Every pregnant woman has equal access to prenatal screening, and medical staff are responsible for providing prenatal screening information for pregnant women. Prenatal screening is conducted on the basis of informed choice and voluntary motherhood. Second, prenatal diagnosis 1. What is prenatal diagnosis: on the basis of genetic counseling, prenatal diagnosis of pregnant women with high risk, if it is confirmed as normal fetus, continue pregnancy to full-term production, which is an effective means to prevent the birth of children with severe genetic diseases . 2 Who should do prenatal diagnosis? 2.1 The maternal age is ≥35 years old; 2.2 One of the couples is a balanced translocation chromosome carrier; 2.3 The pregnant mother is a carrier of the sputum-linked recessive genetic disease that cannot be prenatally screened and diagnosed, and needs to measure the sex of the fetus; 2.4 suspected congenital metabolic defects or other genetic diseases capable of DNA diagnosis; 2.5 high-risk couples of chromosomal diseases who have had neural tube defects and chromosomal abnormalities in the past; 2.6 prenatal screening of mother serum markers abnormalities, which are high-risk Pregnant women. 3 prenatal diagnosis methods: 3.1 amniocentesis; 3.2 villus sampling; 3.3 B-mode ultrasound; 3.4 umbilical cord puncture; 3.5 X-ray examination; 3.6 fetal microscopy. Third, Down's syndrome and neural tube defects prenatal screening introduction 1, what is Down's syndrome (Down's syndrome)? Down's syndrome is also known as 21-trisomy syndrome, congenital stupid, congenital dementia . Its characteristics are mainly characterized by severe mental retardation, IQ (IQ) is mostly 20 to 60, only 1/4 to 1/2 of normal people of the same age. It has unique facial and body deformities, such as small head, flat occiput, thick item, small eye crack, lateral upper oblique, deep internal iliac crest, wide eye distance, saddle nose, usually half open, tongue often outside, short fingers Thick, palm prints are coherent, little fingers are bent inside. 50% combined with congenital heart disease, gastrointestinal malformations, leukemia and so on. It has been reported that young women who take longer-term contraceptives can also have a fetus with Down's syndrome. There is currently no effective treatment for this disease, and its incidence rate is about 1% of the number of pregnant women. The birth rate is about 1/600 to 1/700. About 26,600 congenital dementias are born every year in China, and every 20 minutes are born. An example. 2. What is a neural tube defect (NTD)? Neural tube defects are a type of birth defects in the central nervous system and are a polygenic genetic disease. The central nervous system, including the brain and spinal cord, can not be closed when the neural tube is closed during embryonic development, resulting in a neural tube defect, resulting in no brain, spina bifida, hydrocephalus, stillbirth or death after birth. Survivors usually have a spirit. And physical defects. Spina bifida is usually caused by the inability of the spine to be completely locked during embryogenesis; the absence of brain is caused by abnormal development of the brain and skull. In foreign countries, there are many spina bifurcations, while in the country, there are many brainless children. The incidence of neural tube defects (NTD) in the northern provinces of China is higher, and the incidence of NTD in Shanxi Province is >1%. Women who have developed children with neural tube defects (NTD) and her female relatives constitute a high-risk group. 3. Who will give birth to a "congenital fool"? Every pregnant woman has the opportunity to give birth to a "congenital type of child". Its occurrence is accidental and random. There is no warning beforehand, no family history, no clear history of poison contact, and the incidence will increase with the age of the pregnant woman. Raise. However, 80% of the congenital children are born of young pregnant women under 34. Therefore, we only say that every pregnant woman has the opportunity to give birth to a congenital child! 4. Is it possible to treat a "congenital child" who has been born? How to avoid birth? Medically, it is incurable to the "congenital type". Because the congenital type is an autosomal disease caused by the addition of one to the 21st chromosome. The way to prevent this type of disease is to conduct prenatal screening and necessary prenatal diagnosis during pregnancy, and to detect and take appropriate measures (such as termination of pregnancy) as soon as possible. 5. In addition to Down's syndrome, the proportion of other chromosomal abnormalities in 10,000 births is chromosomal abnormality type and survival time. Trisomy syndrome (Down's syndrome) is 1/150 in fertilized eggs; The child is 1/600. About 35 years old. Trisomy 18 (Edwards syndrome) is 1 in 1000 in newborns. About 1 year old. Trisomy 13 (Patau syndrome) is 1 in 5000 in neonates. The survival rate over 6 months is 5%. 6, the principle of prenatal screening: the use of serum markers for prenatal screening Down syndrome (DS) and neural tube defects (NTD) are getting more and more attention and widely used. The currently used serum markers for screening Down's syndrome (DS) and neural tube defects (NTD) are: alpha-fetoprotein (AFP), beta-chorionic gonadotropin (Free-β-HCG/β-HCG) ), pregnancy-related plasma protein (PAPP-A). It is reported that 93% of the fetuses have at least one marker abnormality, and more than 90% of Down's syndrome (DS) have more than two marker abnormalities. Down syndrome (DS) was screened using a combination of serum markers. At present, the commonly used combination is the binary method or the triple method, and even the six or seven links. However, from the perspective of health economics and social benefits, it is the most ideal choice to select the least combination of indicators to achieve the maximum prediction effect. In the early pregnancy (7-13 weeks gestation), the positive detection rate of DS in the β-HCG+PAPP-A combination was the highest in the 7-13 weeks of pregnancy. In the second trimester (14-21 weeks gestation) AFP+β-HCG+ uE3 is the first combination used and is currently the most widely used combination in the world, known as the traditional triple marker combination. The most sensitive period of this combination is 14-21 weeks of pregnancy, and the positive detection rate of Down's syndrome (DS) is 65%-80%, and the detection rate is higher for pregnant women. uE3 is controversial as a mark, and many laboratories have given up on this indicator. 6.1 Screening of pregnant women's age: As the age of pregnant women increases, chromosomes may not separate, so the risk of pre-eclampsia is increased. The threshold for screening for pregnant women's age is set at 35 years old, which is equivalent to a risk of 1:400, that is, pregnant women aged 35 and over are at high risk. A 20-year-old pregnant woman has a 1/1528 chance of giving birth to a congenital, a 30-year-old pregnant woman with a 1/909 chance, while a 35-year-old pregnant woman is increased to 1/350. However, it should be noted that although the chances of a high-born mother giving birth to a "congenital type of child" are relatively high, women who are over 35 years old in our country are only a minority of pregnant women, and most of them are younger women. Screening for the age of pregnant women is generally not used clinically, but the risk associated with the age of the pregnant woman can be used to calculate the overall risk rate for screening for serum markers in pregnant women. 6.2 Screening of maternal serum markers: 6.2.1 alpha-fetoprotein (AFP) (1) alpha-fetoprotein (AFP) during normal pregnancy: alpha-fetoprotein (AFP) is the main protein in early embryonic origin, derived from the fetal liver and Yolk sac. The synthesis begins on the 20th day of the embryo. At the 14th to 16th week, AFP can be detected in the blood of the pregnant woman, and the AFP in the fetal blood is infiltrated into the mother blood through the placental barrier through the amniotic fluid. AFP in pregnant women's serum gradually increases in early and middle pregnancy. At about 28-32 weeks, the amount of AFP in maternal blood reached the highest peak and was relatively stable, and then gradually decreased. AFP is a specific globulin of the fetus with a molecular weight of 64,000-70000 Daltons. It may have immunoregulatory functions of glycoprotein during pregnancy to prevent fetal rejection by the mother. AFP is synthesized from the yolk sac in the first 1-2 months of pregnancy, followed by synthesis from the fetal liver. The fetal digestive tract can also synthesize a small amount of AFP into the fetal blood circulation. At 6 weeks of gestation, the AFP value of fetal blood increased rapidly and reached the peak at 13 weeks of gestation. After that, the pregnancy progressed gradually to full term. The AFP in amniotic fluid mainly came from fetal urine. The change trend was similar to that of fetal blood AFP. Amniotic fluid and fetal blood, but not consistent with the trend of amniotic fluid and fetal blood. In early pregnancy, maternal blood AFP concentration is the lowest, gradually increasing with the progress of pregnancy, peaking at 28-32 weeks of gestation, and then decreasing. (2) Alpha-fetoprotein (AFP) is a marker of open neural tube defects and Down's syndrome: it is because the fetus produces a large amount of AFP and only a small amount of AFP can enter the mother, so AFP can be used as a certain fetal defect. index. The elevated AFP in the maternal serum during pregnancy is all from the fetus, about two-thirds through the placenta into the mother, and one-third through the amnion into the mother. In pregnant women with Down's syndrome, the maternal serum AFP level is about 23% lower than normal pregnancy, but we do not know the reason for the decrease in AFP levels in Down's syndrome. In pregnant women with open neural tube defects, AFP levels in AFP and amniotic fluid can be 80-90% higher than normal pregnancy, but closed neural tube defects, even with cerebral edema, AFP levels in pregnant women are still normal. 6.2.2 Chorionic gonadotropin (hCG) (1) Chorionic gonadotropin (hCG) during normal pregnancy hCG is a sugar composed of two non-covalent subunits (alpha subunit and beta subunit) protein. hCG is synthesized from the placenta. Certain tumors such as teratomas and choriocarcinoma also secrete hCG. The concentration of hCG in the fetal circulation is about 3% of the maternal serum concentration. The fetal hCG is significantly increased in early pregnancy, reaching a high level (1500-2500 mIU/mL) at 8-10 weeks of gestation, and then gradually decreasing to a stable level at 18-20 weeks. The concentration of hCG in maternal serum peaks at 10 weeks of gestation. Period (100,000 mIU/mL), then down to a stable level (20,000 mIU/mL) at 18-20 weeks. The change in hCG content in amniotic fluid is similar to changes in fetal circulation, and hCG is difficult to detect in non-pregnant women, newborns and men. (2) Chorionic gonadotropin (hCG) is a marker of Down's syndrome. The content of hCG in the mother's serum and amniotic fluid in the fetus with Down's syndrome is 2.08 times that of the normal pregnancy in the second trimester. The hCG content in amniotic fluid is 1.7 times higher than normal pregnancy in the second trimester. The pathophysiological reasons for elevated hCG levels in Down's fetal pregnancy are associated with increased placental secretion. (3) Free chorionic gonadotropin (Free-β-hCG) and intact chorionic gonadotropin (hCG) intact hCG is composed of α subunit and β subunit. The alpha subunit is identical to the alpha subunit of other pituitary hormones, and only the beta subunit is unique to hCG. In the second trimester, more than 99% of the hCG in the maternal serum is present in intact form, and only about 0.5% of hCG is present in the free beta subunit. In 1990, it was reported that the use of free β subunits could increase the detection rate of Down's fetus by 20%. However, this report did not compare with the complete hCG. The Foundation of Blood Research found that the detection rates of free β-subunits and hCG combined with other markers were 54-62% and 55-62%, respectively, while British studies found beta subunits and hCG and other markers. The detection rates of the combination were 67% and 69%, respectively, which showed that the distribution of the β subunit and intact hCG was very similar in the affected population and the normal population. The hCG in the specimen decomposes into the β subunit and the α subunit as time elapses and the temperature increases. Since the free beta subunit is very low in serum, the decomposed beta subunit will largely affect the detection level of the beta subunit, while the effect on intact hCG is relatively small. Therefore, using the beta subunit as an indicator may increase the false positive rate. For this reason, the laboratory should avoid the increase in temperature when transporting or storing specimens. 6.2.3 Pregnancy-associated plasma protein (PAPP-A) (1) Pregnancy-associated plasma protein (PAPP-A) pregnancy-associated protein (PAPP-A) in normal pregnancy is a macromolecular glycoprotein with a molecular weight of 750,000 Carlton, which accounts for 20% of carbohydrates, is not fully understood. PAPP-A is produced by the placenta syncytiotrophoblast and decidua, belongs to α2 macroglobulin, has the function of activating complement and plays an immunosuppressive role. It can be detected in maternal serum in the first trimester, but not in fetal blood during the whole pregnancy. Road PAPP-A, this is because PAPP-A has a large molecular weight and cannot enter the blood circulation through the placenta. It has the following advantages: it can be detected in maternal blood in the early pregnancy stage. When other maternal protein levels begin to decline, maternal blood PAPP-A levels are still rising, it is the only pregnancy protein with the highest concentration in maternal blood, followed by amniotic fluid, and not contained in fetal blood. As the pregnancy progresses during normal pregnancy, the maternal PAPP-A level continues to rise to the peak at the full term of pregnancy. It can be measured in the serum of pregnant women at 6 weeks of gestation and increases with the increase of gestational age, but there is no peak until full term. All organs of Down's syndrome including the placenta are underdeveloped, the function of placental syncytium trophoblast is decreased, and the synthesis of PAPP-A is reduced. Therefore, low levels of PAPP-A in early pregnancy are a good indicator for screening chromosomal abnormalities in the fetus, especially in the Down syndrome fetus, with a detection rate of up to 60%. In addition, when spontaneous abortion, ectopic pregnancy, fetal growth retardation, fetal death, the maternal blood PAPP-A also showed a low value, which is related to placental insufficiency, resulting in reduced synthesis. PAPP-A can be used as an indicator to determine the function of the placenta and predict the degree of fetal risk and the development of pre-eclampsia. (2) PAPP-A is a marker of Down's syndrome: PAPP-A is a serum index for screening Down's syndrome in early pregnancy (before 14 weeks). PAPP-A in the maternal blood of Down's syndrome showed a downward trend. In pregnant women with a congenital fetus, the serum (PAPP-A) is generally less than 0.25MOM to 0.51MOM. 6.2.4 Prenatal screening for Down's syndrome. In the first trimester (7-13 weeks of pregnancy), the pregnancy-associated protein (PAPP-A) in the serum of pregnant women with Down syndrome showed a downward trend, and β-chorionic gonadotropin (Free-β-HCG/β-HCG) showed Increase the trend. Detection of pregnancy-related protein (PAPP-A) and β-chorion gonadotropin (Free-β-HCG/β-HCG) concentrations in pregnant women, combined with maternal age, weight, gestational age, ethnicity, past medical history, etc. The factors were comprehensively corrected and analyzed to obtain the risk rate of Down's syndrome in pregnancy. The detection rate was about 62%-80%. In the second trimester (14 to 21 weeks of gestation), alpha-fetoprotein (AFP) in the serum of pregnant women with Down syndrome is decreased, and β-HCG is elevated. The concentration of alpha-fetoprotein (AFP) and β-chorion gonadotropin (F-β-HCG /β-HCG) in maternal serum was measured. Combined with the age, weight, gestational age, ethnicity, past medical history and other factors of pregnant women, a comprehensive correction analysis was conducted to obtain the risk of Down's syndrome in pregnancy. The detection rate was about 67% to 83% or higher. 6.2.5 Prenatal screening of neural tube defects In the second trimester (14-21 days of gestation), the abnormality of alpha-fetoprotein (AFP) in amniotic fluid and maternal serum is significantly increased in neural tube defects (such as no brain, open spina bifida, etc.). High, by detecting the concentration of AFP in the mother serum, combined with the weight, gestational age, ethnicity, past medical history and other factors of the pregnant woman, the open neural tube defect fetus can be screened. In children with neural tube defects, the level of maternal serum AFP is increased in tonicity, generally >2.5MOM. It is currently irreplaceable by other markers, and the detection rate can be as high as 85%. 7. What is the best time for prenatal screening and for the disease? (1) Mid-pregnancy screening and early pregnancy screening: Advantages and disadvantages Early screening early diagnosis 1. During this period, pregnant women rarely come to the hospital; 2. Need to do AFP testing in the medium to screen for open neural tube defects; 3. The risk of amniocentesis and chorionic villus sampling is increased; Technical difficulty of ultrasonic NT measurement. Mid-term screening Has many years of screening experience 2. The safety of amniocentesis or chorionic villus sampling increased by 3. Simultaneous screening for open neural tube defects The diagnosis is late. (2) Target stage I: Early pregnancy (7-13 weeks of pregnancy) Two-way method (PAPP-A + β-HCG (F-β-HCG/β-HCG)) is used to report the fetal risk of Down syndrome rate. Stage II: mid-pregnancy (14-21 weeks of gestation) using a binary method (AFP+β-H CG (F-β-HCG/β-HCG) or triple-method β-HCG (F-β-HCG/β-HCG) +PAPP-A or AFP+β-HCG (F-β-HCG/β-HCG)+PAPP-A), reporting the risk of Down's syndrome and the risk of neural tube defects. 8, Down's syndrome (DS) and neural tube defects (NTD) prenatal screening flow chart: 8.1 Down's syndrome (DS) prenatal screening flow chart: Note: MSAFP - maternal serum alpha-fetoprotein; AFAFP - amniotic fluid alpha-fetoprotein; MOM - mean median multiple (middle multiple). 8.2 Neural tube defect (NTD) prenatal screening flow chart: Note: MSAFP - maternal serum alpha-fetoprotein; AFAFP - amniotic fluid alpha-fetoprotein; ONTD - open neural tube defects; ACHE - acetate cholinesterase MOM - mean median multiple (middle multiple) IV. Prenatal screening system The prenatal screening system consists of in vitro diagnostic reagents, testing instruments and screening analysis software. The detection instrument is combined with the in vitro diagnostic reagent to detect the amount of the marker (alpha-fetoprotein, β-chorionic gonadotropin, pregnancy-related plasma protein) in the serum of the pregnant woman, and the test data is input into the screening analysis software to obtain the Down's Results of syndrome (DS) and neural tube defect (NTD) screening. 1. Screening and analysis software: Down's syndrome (DS) and neural tube defects (NTD) prenatal screening analysis software is suitable for hospitals for early pregnancy (7-13 weeks) and second trimester (14-21 weeks) Screening for Down syndrome (DS) and neural tube defects (NTD). The software can be applied to the analysis of the results of detection methods such as enzyme-linked immunosorbent assay (ELISA), chemiluminescence (CIA), radioimmunoassay (IRMA), and time-resolved fluorescence immunoassay (TRFIA). The screening and analysis software has been developed by Zhuhai Aibolu Biotechnology Co., Ltd., which collects and establishes a database of Chinese population and a positive likelihood ratio data judgment model for screening, and combines the detected maternal serum marker data with pregnant women. A comprehensive corrective analysis of factors such as age, weight, gestational age, ethnicity, and previous medical history led to the risk of Down's syndrome in pregnancy. Its characteristics: (1) suitable for the Chinese population; (2) applicable to a variety of testing methods, without the need to purchase special instruments and equipment. The user can carry out prenatal screening work according to existing instruments and equipment. Considering the sharing of resources, it is generally recommended to use enzyme-linked immunoassay; (3) detection of gestational age (7-21 weeks of gestation); (4) comprehensive factors: 1 age; 2 weight; 3 weeks of gestation; 4 races; 5 past medical history (insulin-dependent diabetes); 6 serum marker data. 2, the results of the analysis: 2.1 Down syndrome interpretation: 2.1.1 Down syndrome (DS) risk rate cut-off value (cut-off value): prenatal screening Down syndrome (DS) fetal risk rate cut-off value (cut-off value) should be set to be in the range of 1:150 to 1:300. The determination of the risk rate cut-off value (cut-off value) should be combined with the detection rate and the false positive rate (the differences between the laboratories can be determined based on the local population statistics). 2.1.2 Down syndrome (DS) risk rate ≥ risk rate cut-off value, it is judged as Down's child high risk pregnant women (ie, Down's syndrome screening results are positive), it is recommended to conduct prenatal diagnosis; The risk rate of 2.5MOM is judged as a high-risk pregnant woman with neural tube defect (ie, the neural tube defect screening result is positive), it is recommended to conduct prenatal diagnosis; conversely, if the multiple of AFP is <2.5MOM, it is judged as a neural tube defect fetus. Low-risk pregnant women (ie, negative for neural tube defect screening), no further examination. Repeated serum assays were considered significant when AFP was mildly elevated (2.50 MoM). For example, if the second AFP is between 1.0 and 2.0 MoM, the fetus may be normal. 2.2.3 AFP elevation may include the following: 1) neural tube defects; 2) signs of high-risk pregnancy such as abortion, premature birth, low birth weight or gestational eclampsia; 3) other malformations: stillbirth, spastic salvage, abdominal wall defects , congenital nephropathy, upper gastrointestinal obstruction; 4) normal variation: unexplained MSAFP increase in pregnant women; 5) multiple births; 6) incorrect gestational age calculation. AFP reduction includes the following: 1) Down's syndrome; 2) no pregnancy; 3) other malformations: undiscovered abortion and missed abortion; 4) normal variation; 5) incorrect gestational age calculation. 2.2.4 HCG elevation may include the following: 1) stillbirth; 2) premature birth; 3) neonatal death; 4) low body weight or gestational eclampsia 5) Down's syndrome. 2.2.5 PAPP-A reduction may include the following: 1) Down's syndrome; 2) spontaneous abortion, ectopic pregnancy, fetal growth retardation, stillbirth; 3) fetal high risk or pre-eclampsia. 2.3 Risk rate cut-off value on screening positive rate and 21 trisomy detection rate category 1:190 mid-pregnancy cut-off value 1:270 mid-pregnancy cut-off value screening positive case 1141 (7.1%*) 1508 (9.4%) amniotic cavity Puncture cases 533 (3.3%) 725 (4.5%) 21 Trisomy test cases 131421 Trisomy detection rate 56% 60% detected a case of 21 trisomy amniocentesis 4051 * original positive rate; data from Haddow et al 16067 cases of screening statistics 3, note: 3.1 The software is only suitable for single-fetal pregnant women in the first trimester (nine to 7-13 weeks) and the second trimester (pregnancy 14-21 weeks) prenatal screening for Down syndrome (DS ) and a neural tube defect (NTD) fetus. 3.2 The software can be applied to enzyme-linked immunosorbent assay (ELISA), chemiluminescence (CIA), radioimmunoassay (IRMA), time-resolved fluorescence immunoassay (TRFIA) and other detection methods. 3.3 Determination of gestational age: 3.3.1 Last menstrual period (LMP): Calculated by the first day of the last menstrual period is one of the most commonly used methods; 3.3.2 B-ultrasound (double-top diameter BPD under B-ultrasound): when gestational age ≥ 14 weeks, the last menstrual date is not certain or the number of weeks of pregnancy recorded in the last menstrual period does not match the results of the clinician's examination. It is recommended to use BPD under B ultrasound to determine the gestational age. During this period of pregnancy, BPD determines the gestational age. Accuracy within 10 days, compared with the gestational age determined by LMP, increased the sensitivity of maternal serum screening and reduced the number of false positives. Because, in general, the BPD of spina bifida cases is 2 weeks smaller than normal fetuses, and the gestational week adjusted by BPD improves the sensitivity of screening for spina bifida with maternal serum AFP. It is not recommended to estimate the gestational age by the length of the femur or tibia measured by B-ultrasound, which may become shorter in Down's syndrome. When the serum markers (AFP, β-HCG, PAPP-A) of the pregnant women are abnormal (too high or too low), special attention should be paid to the accuracy of the gestational age. It is recommended that the B-ultrasound should be used to determine the gestational age and eliminate the resulting errors. 3.4 All patients with abnormal experimental results should recommend genetic counseling. The content of the consultation should be reviewed once, the abnormal fetal risk, the patient's choices such as B-ultrasound, prenatal diagnosis, etc. Although the test methods used in prenatal screening are similar to those in clinical tests, the interpretation of the results is different from the general clinical examination. The screening results are related to the risk prediction of fetal abnormalities. The doctor is required to explain the risks to the patients and propose possible choices. 3.5 Experimental reagents must be calibrated with quality or international units. 3.6 The gestational age is calculated using a rounding method (eg 17 weeks + 3 days = 17 weeks, 17 weeks + 4 days = 18 weeks). 3.7 The normal median value of each laboratory shall be calculated and corrected once a year. 3.8 Correction: 3.8.1 Correction of racial differences; 3.8.2 Weight correction of pregnant women, because women with milder women have lower AFP values ​​for mothers; 3.8.3 Pregnant women need to be corrected for insulin-dependent diabetes because insulin dependence The AFP value of pregnant women with diabetes is lower than that of normal people. Moreover, the risk of developing a neural tube defect (NTD) in a pregnant woman is 10 times higher than that of a normal person. However, pregnant women with gestational diabetes do not need to be corrected. 
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