What does early screening mean when Down’s syndrome is high risk?

Down syndrome screening is a non-damaging testing method for the fetus. It is economical, simple and safe and can be performed between 14-18 weeks of pregnancy. Only 2 milliliters of venous blood from pregnant women need to be drawn, and the results will be available to pregnant women 2-3 weeks after the blood draw. If the serum screening test is positive, an amniotic fluid test is required to confirm the diagnosis and treatment methods. Down syndrome screening can also detect high-risk pregnant women with neural tube defects, 18-body syndrome and 13-body syndrome. NT examination is to check the thickness of the fetal nuchal translucency and is often used for prenatal screening. It can early diagnose chromosomal diseases and detect fetal abnormalities caused by various causes. If it exceeds 3mm, it often indicates adverse fetal outcomes

What do AFP and HCG stand for? What do the OD value and MOM value mean? What is the risk of trisomy 21? What is the risk of trisomy 18 and risk of trisomy 13? When getting the Down's syndrome screening report, these questions confuse expectant mothers. Now I will teach you how to read your Down's syndrome screening report.

AFP (alpha-fetoprotein)

AFP is a specific globulin of the fetus with a molecular weight of 64,000-70,000 daltons. It may have immunomodulatory effects on glycoproteins during pregnancy. Function, it can prevent the fetus from being rejected by the mother.

AFP is synthesized by the yolk sac in the first 1-2 months of pregnancy, and then mainly by the fetal liver. The fetal digestive tract can also synthesize a small amount of AFP into the fetal blood circulation. The fetal blood AFP value increases rapidly at 6 weeks of pregnancy, reaching a peak at 13 weeks of pregnancy, and then gradually decreases to term as the pregnancy progresses. AFP in amniotic fluid mainly comes from fetal urine, and its changing trend is similar to fetal blood AFP. Maternal blood AFP comes from Amniotic fluid and fetal blood, but the changing trends of amniotic fluid and fetal blood are not consistent. In early pregnancy, maternal blood AFP concentration is the lowest, gradually increases as pregnancy progresses, reaches a peak at 28-32 weeks of pregnancy, and then decreases again.

The serum AFP level of pregnant women with congenitally stupid fetuses is 70% of that of normal pregnant women, that is, the average MoM value is 0.7-0.8MoM.

Free hCG (free-subunit-chorionic gonadotropin)

Pregnant women with congenital idiopathic fetuses have a tonically elevated serum Free hCG level, with an average MoM value is 2.3-2.4MoM.

In fact, you don’t need to be too nervous because the MOM value of free-hcg is on the high side.

About: hCG is human chorionic gonadotropin synthesized by placental cells and consists of two subunits, a- and b-. HCG exists in two forms, complete hCG and the b-chain alone. Both types of hCG are active, but only the b-single-chain form of hCG is the specific molecule measured. HCG enters the maternal blood 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.

The MOM value is a ratio, that is, the detection value of markers in pregnant women is divided by the median value of normal pregnant women of the same gestational age. This value is MOM. Since the levels of prenatal screening substances vary greatly with increasing gestational age, their values ??must be converted into multiples of the median (MOM) to make them "standardized" to facilitate clinical judgment.

For example: the free-HCG value of a random pregnant woman with a gestational age of 14 weeks and 0 days: 28800mIU/ml

The median of a gestational age of 14 weeks and 0 days is: 14400mIU/ ml

The MOM of this pregnant woman: 28800/14400=2, so if this indicator simply fluctuates, don’t worry too much. It may also be caused by inaccurate calculation of the pregnancy time. There is really no need to let it go. Put yourself into a panic.

About trisomy 21, 18, and 13

Under normal circumstances, people have 46 23 pairs of chromosomes, and trisomy 21, 18, and 13 are the 21st and 23rd pairs of chromosomes in the fetus. The 18th and 13th pairs of chromosomes have one extra chromosome than the normal two, which is called trisomy XX. Trisomy 21 is Down syndrome.

Pregnant women of any age may be pregnant with a fetus with chromosomal abnormalities, but the incidence of chromosomal abnormalities increases significantly as the age of the pregnant woman increases. For example, the incidence of chromosomal abnormalities in pregnant women under the age of 25 is 1:1185, and as high as 1:335 at the age of 25, so pregnant women over 25 years old need to have a chromosome test.

1. Down syndrome screening is a possibility test: high-risk groups only mean that the fetus is more likely to be a child with Down syndrome, while low-risk groups may also have a fetus with Down syndrome

2. About 1/10 of all pregnant women are screened as high-risk groups, and 1 to 2/100 of the high-risk groups are children with Down syndrome, which means that 1 to 2/1000 of pregnant women are children with Down syndrome

3. When the blood test screening value is greater than 1/270, it is a high-risk group. The normal value is about 1/700. The international standard is 1/270

4. The Down syndrome screening value is a modified value. The main factors that affect the screening value of Down syndrome include: maternal age, gestational age, fetoprotein secreted by the fetus, human hormonal hormone secreted by the placenta, drug factors, genetic factors, etc. Eating "Dolly Mom" ??during pregnancy may cause human hormones to exceed normal values ??and may affect Down's syndrome screening values.

The only current medical method to determine whether the fetus is Down syndrome is amniocentesis

Amniocentesis: extract amniotic fluid, culture the cells shed by the fetus in the amniotic fluid, and test the chromosomes of the cells (Testing fetal chromosome 21).

Extract amniotic fluid: Take 20ml of amniotic fluid. The risk is possible infection, amniotic fluid leakage, miscarriage, and the possibility of miscarriage (probability 1/1000)

Cultivation of cells shed by the fetus in the amniotic fluid. The success rate is 98/100.

Check the chromosomes of the cells (check the 21 chromosomes of the fetus). Accuracy 100/100.