What does the quantitative PAPP-A and the free beta HCG (Double test) mean to screen for fetal malformations?

This is an automatically translated article.

The article is professionally advised by: Master. Do Thi Hoang Ha - Doctor of Biochemistry - Laboratory Department, Vinmec Hai Phong General Hospital
One of the paraclinical tests to help screen for fetal malformations at an early stage can include the double test (quantification of PAPP-A and quantification of free β-hCG).

1. What is PAPP-A quantification?

PAPP-A (Pregnancy Associated Plasma Protein A) is a glycoprotein produced by the placenta and secreted into the maternal blood. In a normal pregnancy, PAPP-A levels gradually increase throughout the pregnancy. During the first trimester of pregnancy, if the fetus has an abnormality of chromosomes 21 (Down syndrome), chromosome 18 (Edwards syndrome) and chromosome 13 (Patau syndrome), PAPP-A levels will be observed. in maternal blood decreased, while in the second trimester, the concentration of PAPP-A remained normal or only slightly decreased, therefore, quantification of PAPP-A is only used in the first trimester of pregnancy for prenatal screening (especially in pregnancy). fetus with Down syndrome).

2. What is free beta HCG quantification?

Free β-hCG is a component of the human chorionic gonadotropin (HCG) hormone. Normally, hCG is only present in the blood and urine of pregnant women. HCG is first secreted by the trophoblast cells of the fertilized egg and then secreted by the placenta. HCG is present in the mother's serum about 6 to 8 days after the egg is fertilized and reaches its peak concentration around the 9th week of pregnancy. Thereafter, hormone levels decrease around 1016 weeks of gestation, to about one-fifth of peak levels and remain at this level until the end of pregnancy.

hCG is composed of two chains, α and β, linked together in a complete hormone molecule. The serum of pregnant women mainly contains this intact hCG. However, a small fraction of the α and β subunits circulate as unbound (free β-hCG). The ratio of free βhCG averages 1 % to hCG in maternal blood. If the fetus has Down syndrome, the concentration of the free β-hCG subunit is significantly increased during the first and second trimesters of pregnancy.

3. What is double test?

The double test was performed by measuring the amount of free β-hCG (free beta-human chorionic gonadotropin) and PAPP-A (pregnancy associated plasma protein A) in the pregnant woman's blood, then using a specialized software to calculate the same. with weight, height of mother, gestational age, nuchal translucency (NT) and fetal crown-rump length (CRL) measured by ultrasound,... to assess the risk of disease Down , Edward or Patau syndromes of the fetus in the first trimester of pregnancy (The first trimester of pregnancy is counted when the gestational age is between 11 weeks and 13 weeks and 6 days).
What does the Double test mean for fetal malformation screening?
Biochemical substances such as PAPP-A and free β-hCG are normally produced by the fetus and appear in the maternal blood during fetal and placental development. If the fetus has aneuploidies, the concentration of these substances will change in the mother's blood and their quantification in maternal blood along with ultrasound results... can help assess the risk chance of birth defects such as:
Down syndrome (Trisomy 21), a condition with 3 chromosomes 21, causing intellectual disability and problems with the heart, digestive tract and many other organs . In Down syndrome, the level of free β-hCG is significantly increased, the level of PAPP-A tends to decrease, and the nuchal skin thickness increases. Edwards syndrome (Trisomy 18) is a condition with 3 chromosomes 18. The risk of Edwards syndrome also increases with the age of the mother. Edwards syndrome affects many organs of the body, making children rarely live past one year. If the fetus is at high risk for Edwards, testing will show decreased levels of both free β-hCG and PAPP-A. Patau syndrome (Trisomy 13) is a syndrome caused by having 3 chromosomes 13. Patau syndrome severely affects many organs in the body such as nerves, eyes, heart, kidneys,... Over 80 % of children with Patau syndrome who will die under one year of age. As with Down syndrome and Edward syndrome, the risk of Patau syndrome also increases with maternal age. In Patau syndrome: levels of free β-hCG and PAPP-A are generally low.

4. Specify Double test

All pregnant women should have a double test. Especially those at high risk such as:
Age over 35. Ever had a miscarriage or stillbirth of unknown cause. Have been pregnant or had a baby with a birth defect. Family history of having a child with a birth defect. Diabetes and insulin use Smoking. Are using drugs or chemicals that can harm the fetus Viral infection during pregnancy. Exposure to radiation There are abnormal findings or suspicions on ultrasound results.

5. Does the Double test result confirm that the fetus has Down syndrome or Edwards, Patau?

Test results only allow conclusions about the risk of having Down syndrome or Edwards, Patau.

6. If the test results show an increased risk to the fetus, what does this mean?

Screening results showing an increased risk of having a fetus with Down syndrome or trisomy 18 or 13 does not mean that the fetus has been diagnosed with that chromosomal abnormality, but simply fetuses are at increased risk of Down, Edwards, and Patau syndromes. Your doctor will advise on further tests that need to be done to make a diagnosis such as chorionic villus sampling or amniotic fluid collection for fetal cytology, these tests allow for an accurate diagnosis of up to 99.9%. fetus with a chromosomal abnormality.

7. Equipment used to quantify PAPP-A and measure free beta HCG (Double test)

Part of the antenatal screening test kit (Double test - PAPP-A, free bHCG) which is now included in the routine tests specified in obstetric examination packages with the goal of safety for the mother and the baby's health. . At Vinmec Health system, the nasal bone index (Nasal Bone) is used to support the diagnosis of fetal malformations (In Hai Phong alone, currently only Vinmec Hai Phong International General Hospital uses the index. this).
This test kit is essential to screen, based on the results obtained high or low risk, what type of high risk malformation is to guide in-depth tests for diagnosis.
The test runs on Roche's immune system and Beckman Coulter's immunoassay system in compliance with strict test quality management procedures, ensuring accurate test quality for diagnostic and therapeutic purposes. effective treatment.

Quantification of PAPP-A, Quantification of free beta HCG (Free Beta Human Chorionic Gonadotropin) - Double test is one of the services included in the 12-week maternity package of Vinmec International General Hospital.
Maternity package package is the most perfect choice to help the pregnancy journey be completely secure, early regular check-ups will help to comprehensively assess the situation of mother and baby, pregnant women will be counseling, treatment and early adjustment directions when unfortunately the fetus has problems. Currently, Vinmec has many maternity packages such as 12-week maternity, 27-week, 36-week maternity package and labor package. In which, the 12-week maternity package is becoming the choice of most pregnant women when coming to Vinmec.

Why should you choose Vinmec maternity package?
Vinmec has an international standard infrastructure system and is built in the model of a high-quality hospital - hotel. Registering for Vinmec maternity package, pregnant women will experience perfect services with state-of-the-art medical infrastructure. The medical team - doctors who are leading experts in the industry, have specialized qualifications and many years of experience in the profession, always dedicated and dedicated to taking care of patients. The space for medical examination and treatment is modern, luxurious and sterile. And many other benefits, you will experience when you sign up for the 12-week maternity package at Vinmec. Customers can directly go to Vinmec Health system nationwide to register for maternity package or contact hospitals and clinics of Vinmec Health system nationwide.

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