How many days does it take for Down syndrome screening to produce results?

Down syndrome screening is a detection method that extracts serum from pregnant women, detects the concentration of various substances in the maternal serum, and combines multiple physiological indicators of the pregnant woman to calculate the risk factor of giving birth to a fetus with congenital defects. It is our main means of prenatal testing. Many expectant fathers and mothers are more concerned about how many days it will take for the results of Down syndrome screening to come out. Let us learn about it.

The results of Down syndrome screening are generally available within two weeks. This is because the current Down syndrome screening test tests the concentration of alpha-fetoprotein (AFP) and human chorionic gonadotropin (β-hCG) in the pregnant woman's blood, and combines it with the pregnant woman's age to use a computer to accurately calculate the risk of each pregnant woman carrying a fetus with Down syndrome. Alpha-fetoprotein (AFP) generally ranges from 0.7-2.5 MOM. The higher the level of chorionic gonadotropin, the higher the chance that the fetus will have Down syndrome. In addition, the doctor will input the alpha-fetoprotein value, human chorionic gonadotropin value, and the pregnant woman's age, weight, and weeks of pregnancy into the computer, which will calculate the risk of the fetus developing Down syndrome. Different hospitals use different standards. If the probability indicated by the test result (such as 1/100) is greater than the normal reference value probability (such as 1/275), the result is positive, indicating that the fetus has a higher chance of being sick and further amniocentesis or chorionic villus sampling should be performed. (1) AFP (alpha-fetoprotein): AFP is a fetal-specific globulin with a molecular weight of 64,000-70,000 Daltons. It may have the immunoregulatory function of glycoprotein during pregnancy and 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 synthesized by the fetal liver. A small amount of AFP can also be synthesized in the fetal digestive tract and enter the fetal blood circulation. The fetal blood AFP value increases rapidly at 6 weeks of gestation, reaches a peak at 13 weeks of gestation, and then gradually decreases as the pregnancy progresses to full term. The AFP in amniotic fluid mainly comes from fetal urine, and its change trend is similar to that of fetal blood AFP. Maternal blood AFP comes from amniotic fluid and fetal blood, but its change trend is not consistent with that of amniotic fluid and fetal blood. In early pregnancy, the maternal blood AFP concentration is the lowest, gradually increases as the pregnancy progresses, reaches a peak at 28-32 weeks of pregnancy, and then decreases. The serum AFP level of pregnant women carrying congenitally retarded fetuses is 70% of that of normal pregnant women, that is, the average MoM value is 0.7-0.8MoM. (2) FreehCGβ (free-β subunit-human chorionic gonadotropin): Pregnant women with congenitally retarded fetuses have a tonic increase in serum FreehCGβ levels, with an average MoM value of 2.3-2.4MoM. In fact, you don’t need to be too nervous if the MOM value of free-hcg is a bit high. About: hCG is human chorionic gonadotropin synthesized by placental cells and is composed of two subunits, a- and b-. HCG exists in two forms, intact 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 for measurement. 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 marker detection value in the pregnant woman's body divided by the median value of a normal pregnant woman at the same gestational age. This value is the MOM. Because 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" and facilitate clinical judgment. For example: The free-HCG value of a random pregnant woman with a gestational age of 14 weeks + 0 days is: 28800mIU/ml. The median of the gestational age of 14 weeks + 0 days is: 14400mIU/ml. The MOM of this pregnant woman is: 28800/14400=2. Therefore, if this indicator alone fluctuates, don't worry too much about it. It may also be caused by inaccurate calculation of the pregnancy time. There is really no need to panic. (3) Regarding trisomy 21, 18, and 13, normally humans have 46 chromosomes in 23 pairs. Trisomy 21, 18, and 13 means that the fetus has one more chromosome in the 21st, 18th, and 13th pairs than the normal two, which is called XX trisomy. Trisomy 21 is Down syndrome. Pregnant women of any age may have a fetus with chromosomal abnormalities, but the incidence of chromosomal abnormalities increases significantly with the age of the pregnant woman. For example, the incidence of chromosomal abnormalities in pregnant women under 25 years old is 1:1185, while at the age of 25 it is as high as 1:335. Therefore, pregnant women over 25 years old need to undergo chromosomal examinations. That’s why Down syndrome screening results are usually available within two weeks.

After reading this article, do you know why it takes two weeks to get the results of Down syndrome screening? Therefore, we don’t have to be anxious. After going to the hospital for a check-up, we just need to continue to rest and take care of the fetus at home. Maintaining a good attitude and a happy mood during pregnancy is the correct way to give birth to a healthy and smart baby. Finally, I wish you all good health and that your future babies will be smart.