Down Syndrome Screening

Down Syndrome Screening

At the Istenhegyi Genetic Diagnostics, Gynecological and Family Planning Center, we screen for Down syndrome with up to 100% certainty and without jeopardizing the health of the mother and the fetus, with the help of state-of-the-art fetal genetic tests, qualified doctors and laboratory.

What is Down syndrome?

Down syndrome is an aneuploidy, more precisely trisomy 21: in this case, cells contain three copies of chromosome 21 instead of two copies. Since in 95% of the cases, this condition is not hereditary, fetal genetic tests may help in detecting this aneuploidy. Without preventive tests, approximately one in 500-600 babies would be born with this condition. The best known symptoms of Down syndrome include severe mental retardation and physical disorders.

The incidence of Down syndrome increases with maternal age. In Hungary, pregnant women over the age of 37 are offered a fetal genetic test, but this intervention increases the risk of miscarriage by 0,5-1%. However, Down syndrome can be detected in time and with high accuracy using risk-free tests provided by our Center; all there is needed is a genetic ultrasound examination and maternal blood sampling.

Since in women under the age of 37, Down syndrome screening is not routinely done, at the present the vast majority of babies with Down syndrome are born to younger mothers. Therefore, at this institute we recommend to all expecting mothers, regardless of their age, to choose one of the risk-free Down syndrome screening tests.

Screening options for Down syndrome

The key pillars in Down syndrome screening during pregnancy are repeated ultrasound tests and blood tests. There are many methods for Down syndrome screening; at the Istenhegyi Genetic Diagnostics, Gynecological and Family Planning Center the following tests can be used:

Test 1st trimester
Week 12-14
2ndtrimester
Week 16-19
Result
Combined test blood sampling + genetic ultrasound In the 1st trimester, within 1-1.5 hours
Nifty-test maternal blood sampling between the 10th to 18th weeks in 7 working days
Trisomy-test maternal blood sampling between the 11th to 19th weeks in 7 working days

Accuracy of Down syndrome screening tests

Test False positive rate * Sensitivity**
Combined test 1-2 % 90-95%
Nifty-test < 1% >99%
Trisomy-test < 1% >99%

 

*False positive rate: the proportion of non-Down syndrome pregnancies that will have (false) positive test results
**Sensitivity: the probability that the screening test will give a positive result in the case of fetuses with Down syndrome

What is a combined test?

The combined test can be carried out between the 11th to 14th weeks of pregnancy by combining ultrasound tests and blood tests.

During the ultrasound test in the first trimester, in addition to the measurement of fetal dimensions, we concentrate on early detection of both developmental abnormalities and deviations indicative of chromosome aberrations. Down syndrome can be screened efficiently by measuring nuchal translucency and by evaluating the presence of the nasal bone. Moreover, the evaluating physician will also examine smaller signs, but these usually cannot be used in determining specific risks; they can help in determining further examinations in case of doubtful results.

You ought to know!

“The result of the ultrasound test in the first trimester can be accepted for risk assessment only if this test was carried out according to FMF criteria and the person carrying out the test holds a FMF license. Although according to the literature data, this is the most efficient method to screen for trisomy 21, adequate efficacy can be achieved only if the measurement is carried out in an appropriate plane with an accuracy of 0.1 mm, for which an adequate device, adequate expertise, experience and time to achieve precise setting are essential prerequisites.”

Egészségügyi Közlöny (Health Gazette), 2010. No. 4, page 1170: Az Egészségügyi Minisztérium szakmai protokollja a Down-kór prenatális szűréséről és diagnosztikájáról (Medical protocol of the Ministry of Health on the prenatal screening and diagnostic of Down syndrome)

At the Istenhegyi Genetic Diagnostics, Gynecological and Family Planning Center, we employ exclusively physicians who have passed the FMF exam. The full list of Hungarian physicians who have passed the FMF examination can be accessed on the webpage of Fetal Medicine Found.

The blood test, which is part of the combined test, is carried out by the qualified laboratory of the Genetic Diagnostic Center to determine the concentration of two fetal proteins produced by the placenta. This combined test produces results within 1-1.5 hours.

What is the Nifty test?

The NIFTY test is a maternal blood test used to detect Down syndrome and two other aneuploidies (Edwards syndrome and Patau syndrome), the differences in the number of sex chromosomes (X and Y; Klinefelter syndrome, Turner syndrome, double Y syndrome, triple X syndrome) and deletion syndromes during pregnancy. At the present, this is the so-called non invasive, state-of-the-art test in the screening for Down syndrome; non invasive means that there is no need for sampling that puts the fetus at risk.

This test is based on the fact that during pregnancy fetal genetic material (DNA) gets into the maternal blood in a proportion of up to 10-15% compared to the maternal DNA. Fetal DNA can now be detected in maternal blood with sufficient accuracy. The reliability of the NIFTY test exceeds the reliability of any other blood tests: in the case of pregnancies tested so far this new test screened for all fetuses with Down syndrome, Edwards syndrome or Patau syndrome.

A detailed description of the Nifty test can be accessed on niftytest.com.

What is the Trisomy test?

The TRISOMY test is a maternal blood test used to detect Down syndrome and two other aneuploidies (Edwards syndrome and Patau syndrome) during pregnancy. At the present, this is the so-called non invasive, state-of-the-art test in the screening for Down syndrome; non invasive means that there is no need for sampling that puts the fetus at risk.

This test is based on the fact that during pregnancy fetal genetic material (DNA) gets into the maternal blood in a proportion of up to 10-15% compared to the maternal DNA. Fetal DNA can now be detected in maternal blood with sufficient accuracy.

A detailed description of the Trisomy test can be accessed on trisomytest.hu.

Which Down syndrome screening test should I choose?

At the Istenhegyi Genetic Diagnostic Center, we primarily recommend the combined test because is a rapid and reliable test (with an accuracy of 90-95%). We make recommendation for further tests after the evaluation of the result of the combined test.

The Trisomy and NIFTY tests, due to them high reliability (99.9%), they can be used really well in the following cases:

  • instead of the quadruple test with an accuracy of 80% in itself at the beginning of the second trimester,
  • in case of intermediate risk, that is, if the combined test shows that the risk of Down syndrome is between 1:150 and 1:1000,
  • if the parents want a test with a reliability higher than that of the combined test or sequential screening.

Unlike other tests, the Trisomy and NIFTY tests give clear results and they are expected to be launched as a non invasive (not posing a threat to the fetus) diagnostic method after the clinical trials are completed, to replace current invasive diagnostic methods.

We will help you take a decision

Future parents will be provided with detailed information on screening methods during genetic counseling before screening. The screening method will be selected based on maternal age, gestational age and possible earlier abnormal pregnancy/pregnancies. All these factors determine the estimated risk of fetal abnormalities, and our experts will make specific proposals for the best method for Down syndrome screening based on these data.

Registration for Down syndrome screening

Place of screening: Istenhegyi Genetic Diagnostic, Gynecological and Family Planning Center

1125 Budapest, Zalatnai utca 2. (Map)

To register, please contact us at phone +36 1 580 8600.

Additional tests depending on the result of the combined test.

Women who underwent the combined test between the 11th and 14th weeks can be classified into three groups based on the results obtained.

The first, low-risk group will include women in whom the risk of Down syndrome is below 1:1000. In their case, the genetic ultrasound examination should be carried out between the 18th and 20th weeks.

The second, intermediate-risk group will include women in whom the risk of Down syndrome is between 1:250 and 1:1000. In their case, using blood sampling in the second trimester allows carrying out sequential screening, or they can choose the Nifty test, which is the screening test with the highest accuracy at the present. Moreover, in pregnant women included in the intermediate-risk group we will analyze malformations specific to Down syndrome using a separate genetic ultrasound test in the second trimester.

The third group includes women in whom the combined test gave positive result. In their case, amniocentesis (AC) or chorionic villus sampling (CVS) is recommended because the Hungarian legislation accepts only these tests as tests with diagnostic value for Down syndrome.

Diagnostic tests: CVS and AC

Chorionic villus sampling (CVS) is required only if the combined test gave positive result. In this case, a thin needle is used to take a sample from the placenta through the abdominal wall. Since the placenta also contains the genetic information of the fetus, the genetic testing of the cells practically confirms or excludes Down syndrome or all changes in the number and rough structure with 100% certainty.

Amniocentesis (AC) is carried out between the 15th and 19th weeks. During an ultrasound examination, a specialist takes a sample of the amniotic fluid, using a needle (through the abdominal wall), which contains fetal cells that are genetically identical with the fetus.

At the Istenhegyi Genetic Diagnostic Center, we always warn future mothers that amniocentesis and chorionic villus sampling are not free of risk and they increase the risk of miscarriage by 0.5-1%. Future mothers will decide whether they agree to the sampling recommended.

Since both CVS and AC are procedures that put the fetus at risk, they can be carried out only with the appropriate indication. These can include among others maternal age above 37, several ultrasound signs, such as thickened nuchal translucency, positive screening test result, maternal or paternal chromosomal aberrations or other genetic abnormalities, and aneuploidy in earlier pregnancy. The need for the intervention is always determined by a geneticist, who will also inform the future mother about risks and alternative options. After genetic counseling, it is always the future mother who will decide whether she wants to undergo the intervention or not.