Down’s syndrome screening is a test that calculates the risk factor for having a fetus with congenital defects by taking maternal serum and testing the concentration of alpha-fetoprotein, chorionic gonadotropin and free estriol in the mother’s serum and combining it with the pregnant woman’s due date, weight, age, weight and week of pregnancy at the time of blood collection.
What is the Down’s syndrome test?
It is an economical, simple and non-invasive test to identify pregnant women at high risk of having certain congenital defects in order to further clarify the diagnosis and minimize the birth rate of abnormal fetuses. Prenatal screening is currently referred to as the detection of pregnant women at risk for congenital defects through the testing of maternal serum markers.
The best time to perform screening is between the 9th and 14th week of pregnancy, called early pregnancy screening, but if you miss it, you will need to go to mid-pregnancy screening, which also allows for risk calculation, but is more damaging to the mother if the final diagnosis is positive. If the result is high risk, there is no need to panic because further chorionic villus biopsy (early stage), amniocentesis and fetal chromosome examination (mid stage) are required for a definitive diagnosis.
Why should I be screened for Down syndrome?
Children with Down’s syndrome have severe mental retardation, congenital stupidity, tongue-stretching dementia, inability to care for themselves, and complex cardiovascular disease, requiring long-term care from their families, which can cause great emotional and financial burdens to the family.
Down’s syndrome is an episodic disease, so every pregnant woman can have a child with Down’s syndrome. The chance of having a child with Down’s syndrome increases with the age of the pregnant woman.
How do I get screened?
The screening test is performed without fasting. Maternal serum is taken and the indicators of pregnancy-associated plasma protein A (PAPP-A), free hCGB subunit (early two) or alpha-fetoprotein (AFP) and chorionic gonadotropin (HCG) and free estriol (uE3) (mid-term three) are measured. “The risk factor for Down’s syndrome can be calculated by combining the expected date of delivery, weight, age and week of gestation at the time of blood collection, so that 80% of Down’s syndrome babies can be detected.
Precautions
During prenatal screening, pregnant women are required to provide more detailed personal information, including birth date, last menstrual period, weight, whether they have insulin-dependent diabetes, twin births, whether they smoke, abnormal pregnancy history, etc. Since the risk rate statistics of the screening test need to be corrected for the above factors, it is also important to fill out the test form before the blood is drawn.
What is Down’s syndrome?
Down’s syndrome is also known as trisomy 21, which means that the patient has one more chromosome than normal (one pair in normal people). The cut-off value is 1/275 (this value may vary due to different methodologies). Greater than is considered high risk and less than is considered low risk. The probability of having Down’s syndrome (DS) in the general population (under 35 years of age) is 1/750.
Down screening test, short for Down syndrome prenatal screening test. The purpose is to determine the risk of the fetus having Down’s syndrome by testing the blood of the pregnant woman. If the results of the screening test show that the fetus has a high risk of having Down’s syndrome, further confirmatory tests – amniocentesis or chorionic villus test – should be performed.
What is the accuracy of the Down screening test?
According to the latest prenatal screening standards of the Ministry of Health, the detection rate of Down screening should be more than 70% by qualified testing units. It is important to clarify that the screening test can only help determine the chance of the fetus having Down’s syndrome, but not whether the fetus has Down’s syndrome. This means that if the blood test is high, the chance of having a baby with Down’s syndrome is higher, but it does not mean that the fetus is definitely defective. For example, if you are over 35 years old, you have a higher chance of having a baby with Down’s syndrome, but it does not necessarily mean that your baby has a problem. On the other hand, even if the test result is normal, it does not guarantee that the fetus will not have the disease.
Pregnant women with a screening test that is above normal should undergo an amniocentesis or chorionic villus test, and only if the amniocentesis or chorionic villus test results are normal can the possibility of Down’s syndrome be 100% ruled out.
What other diseases can be screened for with Down’s syndrome?
Screening for serum AFP, HGG, and uE3 can also screen for pregnancies at risk for neural tube defects (NTD), 18 somatic syndrome, and 13 somatic syndrome.
How do I know the results of the screening test?
Pregnant women will be informed of the results when they return to the clinic for routine prenatal checkups 1 week after blood sampling. If the serum screening is positive, additional chorionic villus biopsy or amniocentesis will be performed to clarify the diagnosis.
Management of high-risk pregnant women
For high-risk pregnant women with trisomy 21 and trisomy 18 in the screening test, the doctor should recommend amniotic fluid fetal karyotype analysis after checking the gestational week and other factors to exclude chromosomes. For high-risk pregnant women with NTD, they should first use ultrasound diagnosis to exclude the possibility of abnormal neurological development and closely observe fetal development, and may also recommend amniocentesis followed by acetylcholinesterase test to It is also recommended to perform acetylcholine enzyme test after amniocentesis to exclude the possibility of closed neural tube abnormality and occult spina bifida.
You can read the report of Down’s syndrome screening
(1) AFP (alpha-fetoprotein)
AFP is a fetal-specific globulin with a molecular weight of 64,000 to 70,000 daltons, which may have immunomodulatory functions as a glycoprotein during pregnancy and may prevent fetal rejection by the mother.
AFP is synthesized by the yolk sac in the early 1-2 months of gestation, and then mainly by the fetal liver, and a small amount of AFP can be synthesized by the fetal digestive tract to enter the fetal blood circulation. AFP in amniotic fluid mainly comes from fetal urine, and its trend is similar to that of fetal blood AFP. Maternal blood AFP comes from amniotic fluid and fetal blood, but its trend is not consistent with that of amniotic fluid and fetal blood. The concentration of maternal blood AFP is lowest in the early stage of pregnancy, and gradually increases with the progress of pregnancy, reaching a peak at 28-32 weeks of gestation, and then decreasing.
Pregnant women carrying congenitally stupid fetuses have serum AFP levels that are 70% of those of normal pregnant women, i.e., the average MoM value is 0.7-0.8 MoM.
In insulin-dependent diabetes mellitus, AFP is 10% lower.
AFP is low in pregnant women with high body weight, 3% higher in smokers, and increased in AFP in abnormal liver function.
(2)Free hCGβ
(Free beta-subunit chorionic gonadotropin)
The serum free hCGβ level is tonicly elevated in pregnant women with congenital dysmorphic fetuses, with an average MoM value of 2.3-2.4 MoM.
In fact, there is no need for people to be too nervous about the high MOM value of free-hcg.
About: hCG is a human chorionic gonadotropin synthesized by placental cells and consists of two subunits, a- and b-. hCG exists in two forms, intact hCG and separate b-chain. Both types of hCG are active, but only the b-single-chain form is the specific molecule for the assay. hCG enters maternal blood right after fertilization and proliferates rapidly until the 8th week of pregnancy, then slowly decreases in concentration until the 18th to 20th week, and then remains stable.
Both maternal serum HCG and β-HCG in congenital fetuses show a continuous increase, generally to the usual maternal values of 1.8-2.3 MOM and 2.2-2.5 MOM
Trisomy 18, β-HCG shows a reduced abnormality, typically ≤0.25 MOM as an important indication of high risk for trisomy 18.
The MOM value is a ratio of the value of the marker in the pregnant woman divided by the median value of normal pregnant women at the same gestational week, which is the MOM. The value must be converted into a multiple of the median (MOM) so that it can be “standardized” for clinical purposes.
For example, the value of free-HCG in a random pregnant woman at 14 weeks + 0 days of gestation: 28,800 mIU/ml
The median of 14 weeks + 0 days of gestation is: 14,400mIU/ml
The MOM of this pregnant woman: 28800/14400=2, so if there are fluctuations in this indicator alone, don’t pay too much attention to it, it may also be caused by the inaccurate calculation of the time of pregnancy, there is really no need to put yourself in a panic.
(3) uE3 (free estriol)
uE3 is the main estrogen produced by the fetal placental unit. The synthesis of dehydroepiandrosterone sulfate, the precursor of uE3, decreases due to fetal adrenal cortical dysplasia, which leads to a decrease in uE3.
Mothers carrying a congenitally stupid fetus exhibit reduced uE3 in their blood with a mean MOM value of 0.7.
(4) About trisomy 21, 18 and 13
Normally, there are 46 23 pairs of chromosomes in human. Trisomy 21, 18 and 13 are the 21st, 18th and 13th pairs of chromosomes in the fetus than the normal 2, which is called trisomy XX. One of the trisomies, trisomy 21, is Down syndrome.
Pregnant women of any age may carry a fetus with chromosomal abnormalities, but the incidence of chromosomal abnormalities increases significantly with the age of the pregnant woman, for example, the chance of chromosomal abnormalities among pregnant women under 25 years old is 1:1185, while it is as high as 1:335 at the age of 35, so senior pregnant women over 35 years old need to have chromosomal examination.
1.Down’s screening is a possibility test: the high-risk group just means that the fetus is more likely to be a Down’s child, and it is also possible to be a Down’s child in the low-risk group
2, in all pregnant women about 1/10 pregnant women screening is a high-risk group, high-risk group 1 ~ 2/100 is Down’s children, that is, in pregnant women 1 ~ 2/1000 is Down’s children.
3, when the blood test screening value is greater than 1/270 for high-risk groups, the normal value is about 1/700. The international standard is 1/270.
4. The Down’s syndrome screening value is a corrected value. The factors that affect the value of Down’s syndrome screening are: maternal age, weight, gestational week, fetal alpha protein secreted by the fetus, human chorionic hormone secreted by the placenta, drug factors, genetic factors, etc. The Down’s syndrome screening value may be affected by the use of “Dolly’s mother” during pregnancy preservation, which may cause the human chorionic hormone to exceed the normal value.
(5) Confirmation method
To determine whether the fetus is Down’s syndrome, the only medical method is to perform amniocentesis, karyotype analysis of fetal cells and enzymatic tests to diagnose chromosomal and metabolic genetic disorders in the fetus.
Amniocentesis: Amniotic fluid is extracted and the cells shed in the amniotic fluid are cultured to test the chromosomes of the cells (test for fetal chromosome 21).
Amniotic fluid extraction: 20 ml of amniotic fluid is taken, the risk is possible infection, amniotic fluid leakage, miscarriage, possibility of miscarriage (probability 0.1%)
Culture of cells shed by the fetus in amniotic fluid, success rate 98%.
Test the cells for chromosomes (test the fetus for chromosome 21) with a 100% accuracy rate
Whether Down’s syndrome screening can detect the sex of the fetus
Down’s syndrome is a common chromosomal disorder in humans. Because children with Down’s syndrome are severely mentally retarded and completely unable to take care of themselves, almost all developed countries now perform Down’s syndrome screening on pregnant women. Free beta HCG is a test of the pregnant woman’s serum, not the fetus.
Importance
Down’s syndrome screening refers to a screening test of special significance, which is performed on a specific group of people without any indication of the corresponding disease (e.g. all pregnant women population), by screening out those of them who are at higher risk of having a certain disease for subsequent diagnostic tests. It is important to clarify that the purpose of screening is not to diagnose a particular disease, but to screen for people with a high probability of developing a particular disease.
The current screening and diagnosis of Down syndrome, trisomy 18, and congenital neural tube abnormalities is one such systematic method, which first screens all pregnant women for fetuses at high risk for three diseases, such as congenital dysmorphism and telangiectasia, for the next diagnostic test, and if the fetus is eventually diagnosed with one of these congenital diseases The pregnant woman can make her own decision about whether to continue the pregnancy.
The same screening method is used for the above mentioned diseases, which means that your age, weight, AFP and beta-HCG levels in your venous blood, along with other conditions (such as smoking or alcohol abuse), are used to calculate the risk of your fetus having each of the three congenital diseases. Depending on the level of risk you will get a positive (high risk) or negative (low risk) result.
The specific method is to draw chorionic blood or amniotic fluid for cell culture, then do karyotype analysis, if there is a 21-trisomy pattern, you can diagnose the fetus as Down syndrome; 2. AFP Chinese name is alpha-fetoprotein, if both maternal blood and fetal amniotic fluid AFP are increased, it confirms that the fetus has neural tube abnormalities, i.e. spina bifida, spina meningeal bulge, anencephaly, microcephaly, hydrocephalus.
Why do we need to do Down’s syndrome screening
Down’s serum screening is a very effective way to check for Down’s syndrome, and any pregnant woman can carry a fetus with Down’s syndrome. It used to be thought that those >35 years of age were at high risk, and that the chances increased with the age of the pregnancy. It is now believed that 80% of Down’s syndrome occurs in.