This is an automatically translated article.
The article is expertly consulted by Master. Doctor Do Thi Hoang Ha - Doctor of Biochemistry - Laboratory Department, Vinmec General Hospital Hai Phong.Double test prenatal screening test to screen for some genetic syndromes for the fetus. Knowing how to read Double test results correctly will help parents better understand the health status of the fetus.
1. What are the results of the Double test test?
Double test is performed by measuring the amount of free β-hCG (free beta-human chorionic gonadotropin) and PAPP-A (pregnancy associated plasma protein A) in the blood of the pregnant woman, and then calculated together with the weight. weight, height of pregnant woman, gestational age and nuchal translucency (NT) as well as fetal crown-rump length (CRL) measured by ultrasound,... thanks to a specialized software to assess the risk of Down (Trisomy 21), Edwards (Trisomy 18) and Patau (Trisomy 13) syndromes in the first trimester of pregnancy.
The above biochemicals are normally produced by the fetus and appear in the mother's blood during development. If the fetus has an aneuploidy, the concentration of these substances will change in the mother's blood. Therefore, their quantification in maternal blood along with ultrasound results,... can help assess the risk of birth defects of the fetus.
Quantitative results of free β-hCG (mU/mL) and PAPP-A (mU/mL) are calculated and corrected by a specialized prenatal screening software according to maternal age (years), gestational age (weeks + days), mother's weight (kg), race, gestational age, head and buttocks length and nuchal translucency measured by ultrasound,... to form a multiple of median MoM (multiple of median), or Corr.MOM coefficients and risk levels of the above syndromes were calculated from these multiple mean values.
Các chỉ số trong xét nghiệm Double test có thể giúp đánh giá nguy cơ dị tật bẩm sinh của thai
2. How to view Double test results
The accuracy of the Double test combined with the results of ultrasound measurement of nuchal translucency for the fetus has the ability to detect fetal malformations in the range of 85-90% for Down syndrome, 5% false-positive and 95%. fetus with Edwards syndrome, Patau syndrome with 0.3% false positive.Safe threshold of fetal malformations
The safety threshold of the fetus with the risk of Down syndrome and Down syndrome according to the mother's gestational age is 1:250. That is, the screening result gives the denominator > 250, the fetus is at low risk, < 250, the fetus is at high risk. The safe threshold for Edwards, Patau syndrome is about 1:100. If the screening result has a denominator > 100, the fetus is at low risk, and if the denominator is < 100, the fetus is at high risk with two syndromes. The safe threshold for neural tube defects is about 1:75. If the screening results indicate that the denominator is >75, the child is at low risk, and vice versa, <75, the child is at high risk. Proportion in screening results
If the result on the test card indicates the risk of Down syndrome is 1:400, it means that the pregnant woman could be one in 400 pregnant women giving birth to a child with Down syndrome, the remaining 399 Pregnant women give birth to children without Down syndrome.
Meaning of the MoM (Multiple of Median) index in the results
The normal values of the parameters of free β-hCG and PAPP-A of pregnant women's blood after correction are all equal to 1 MoM. The low and high cut-off values of the parameters to assess the risk of birth defects are as follows:
b-hCG free < 0.4 or > 2.5 MoM Quantitative PAPP-A < 0 ,4 MoM Because the concentration of biochemical substances above can introduce more or less errors between the results of the test units, the comparison of test results is difficult. Therefore, to overcome the disadvantage of this difference, we use the median multiple - MoM. MoM was calculated by dividing each woman's quantified substance concentration by the median value corresponding to gestational age. Reflects the correlation between the concentration values of substances measured in a pregnant woman compared with the median of the population at the corresponding gestational age, thus allowing a more accurate and convenient assessment when comparing results between different screening centers.
Xét nghiệm Double test kết hợp với siêu âm đo độ mờ da gáy giúp chẩn đoán dị tật thai nhi một cách chính xác
3. Some special cases
The levels of free β-hCG and PAPP-A in maternal blood in the case of diamonic twins at 11 to 13 weeks are about twice as high as that of a singleton and are also higher. compared with monochorionic twins. In this case, the doctor should rely on 4D ultrasound for diagnosis.Therefore, when receiving high-risk Double test results, pregnant women should not be too worried.. Instead, pregnant women should check with other diagnostic methods such as NIPT (non-invasive) method. ) or amniocentesis (invasive) with up to 99.9% accuracy.
Usually, this test is done in the first trimester of pregnancy, usually between 11 weeks 2 days and 13 weeks 6 days. The first 3 months of pregnancy is the most sensitive time during pregnancy, in addition to minimizing fetal abnormalities, parents should note:
Understand early signs of pregnancy, pregnancy poisoning, blood in pregnancy. Timely, correct and sufficient first prenatal check-up, avoiding too early/too late. Fetal malformation screening at 12 weeks detects dangerous fetal malformations that can be intervened early. Distinguish between normal vaginal bleeding and pathological vaginal bleeding for timely intervention to maintain pregnancy. Screening for thyroid disease in the first 3 months of pregnancy avoids dangerous risks before and during delivery. Vinmec currently has many maternity packages (12-27-36 weeks), in which the 12-week maternity package helps monitor the health of mother and baby right from the beginning of pregnancy, early detection and timely intervention of health issues. In addition to the usual services, the maternity monitoring program from 12 weeks has special services that other maternity packages do not have such as: Double Test or Triple Test to screen for fetal malformations; Quantitative angiogenesis factor test for preeclampsia; thyroid screening test; Rubella test; Testing for parasites transmitted from mother to child seriously affects the baby's brain and physical development after birth.
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