How to read the report of Down syndrome screening

What do AFP and HCG mean? What do OD value and MOM value mean? What are the risks of Trisomy 21? What are the risks of trisomy 18 and trisomy 13? When getting the Down syndrome screening report, these questions make pregnant mothers confused. Now I will teach you how to read your Down syndrome screening report.

AFP (high alpha-fetoprotein)

AFP is a specific blood protein of the fetus with a relative molecular mass of 64,000-70,000 Daltons. It may have the hormone regulatory effect of glycoprotein during pregnancy and prevent the fetus from being resisted by the pregnant mother.

AFP is produced by the yolk sac in the first 1-2 months of pregnancy, and then mainly produced by the fetal liver. The fetal digestive system can also produce a small amount of AFP that enters the fetal blood circulation. The fetal blood AFP value increases rapidly at 6 weeks of pregnancy, reaches a peak at 13 weeks of pregnancy, and then decreases slowly with the progress of pregnancy to full term. The AFP in the amniotic fluid of pregnant women mainly comes from fetal urine, and its trend analysis is similar to that of fetal blood AFP. Maternal blood AFP comes from amniotic fluid and fetal blood, but its trend analysis is not consistent with that of amniotic fluid and fetal blood. In the early stages of pregnancy, the maternal blood AFP concentration is the lowest, and slowly increases as the pregnancy progresses, reaching a peak at 28-32 weeks of pregnancy, and then decreases.

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

FreehCG (dispersed-subunit-hcg gonadal hormone)

Pregnant women with congenitally retarded babies have a strong increase in blood cell FreehCG? levels, with an average MoM value of 2.3-2.4MoM.

In fact, the MOM value of free-hcg is higher, so there is no need to be too nervous.

Related: hCG is human chorionic gonadotropin produced by embryonic somatic cells and is composed of two subunits, a- and b-. HCG exists in two forms, complete hCG and independent b-chain. Both types of hCG are specific, but only hCG in the form of b-polypeptide chain is the specific molecule that can be measured. HCG enters the maternal blood after fertilization and multiplies rapidly until the 8th week of pregnancy, then slowly decreases in concentration until the 18th to 20th week, and then remains there for a long time.

The MOM value is a ratio, that is, the reference value of a pregnant woman's body markers divided by the median value of normal pregnant women in the same gestational age. This value is the MOM. Because the levels of prenatal diagnostic substances change significantly with the increase of gestational age, their values ​​must be converted into multiples of the median (MOM) to make them "standardized" and facilitate clinical judgment.

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

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

The MOM of this pregnant woman: 28800/14400=2, so if the value of this indicator fluctuates alone, don't worry too much. It may also be caused by the calculation time of pregnancy. There is really no need to make yourself anxious.

Questions about trisomy 21, 18, and 13

Under normal circumstances, humans have 46 pairs of sex chromosomes. Trisomy 21, 18, and 13 means that the fetus's 21st, 18th, and 13th pairs of sex chromosomes are one more than the normal two, which is called XX trisomy. Among them, trisomy 21 is Down syndrome.

Pregnant women of all ages may have a baby with chromosomal abnormalities, but the incidence of chromosomal abnormalities continues to increase with the age of the pregnant woman. For example, the probability of chromosomal abnormalities in pregnant women under 25 years old is 1:1185, while it reaches 1:335 at the age of 25. Therefore, older pregnant women over 25 years old need to have their chromosomes checked.

1. Down syndrome screening is a possible related examination: the focus is only on the fetus being more likely to be a Down syndrome baby, and there is also the possibility of Down syndrome in the low-risk group.

2. Among all pregnant women, about 1/10 of them are key targets for screening, and among the key targets, 1~2/100 are children with Down syndrome, that is, 1~2/1000 of pregnant women are children with Down syndrome. 3. When the blood test screening value exceeds 1/270, it is a key target, and the standard value is around 1/700. The international standard is 1/270

4. Down syndrome screening value is an adjusted value. The factors that affect the Down syndrome screening value mainly include: the age of the pregnant woman, the number of weeks of pregnancy, fetal fetal protein secreted by the fetus, human chorionic growth hormone secreted by the embryo, drug factors, genetic factors, etc. Taking "Dolly Mama" during pregnancy may cause the human chorionic growth hormone to exceed the standard value and may affect the Down syndrome screening value.

To determine whether the fetus is Down syndrome, the only medical method currently available is amniocentesis.

Amniocentesis: extract the amniotic fluid of the pregnant woman, shape the somatic cells of the fetus in the amniotic fluid of the pregnant woman, and detect the sex chromosomes of the somatic cells (detect the 21 sex chromosomes of the fetus).

Extracting amniotic fluid from pregnant women: Take 20ml of amniotic fluid from pregnant women. The risks are possible infection, leakage of amniotic fluid, miscarriage, and the possibility of miscarriage (probability 1/1000)

The success rate of shaping the fetus from the body cells that fall into the amniotic fluid of the pregnant woman is 98/100.

Detect the sex chromosomes of somatic cells (detect the 21 sex chromosomes of the fetus). Accuracy 100/100.