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Prenatal diagnostics: What betrays tests about unborn babies

2019-09-18T15:02:39.118Z

Some blood and quickly it can be clear whether the baby in the stomach has Down syndrome: Such a test will probably be cash. What can he do? And what concerns are there?


Often, the blood of pregnant women is sufficient to examine the genome of a baby in the womb. Thus, just a few weeks after conception can be tested by means of a blood test, whether the unborn child has the Down syndrome. On September 19, the Federal Joint Committee (G-BA) wants to decide on the issue, which ZEIT ONLINE has dedicated a focus on: "Will the blood test lead to Down syndrome as a cash benefit?"

Female doctors can learn a lot about their offspring in the mother's blood, long before the stomach bulges during pregnancy. Not only the Down syndrome, so a trisomy 21. Even rarer chromosomal peculiarities such as trisomies 18 (Edwards syndrome) and 13 (Pätau syndrome), a wrong number of sex chromosomes X and Y or the DiGeorge syndrome can already be very determine early on the unborn. If the representatives of the medical profession, hospitals, hospitals and insurance companies decide in the Joint Federal Committee, such a blood test for pregnant women would in future be free of charge.

Which women belong to this group? What is the difference between screening and prenatal diagnosis? And what other hereditary diseases or genetic defects hope to recognize human geneticists and prenatal medics as early as possible in the future? ZEIT ONLINE has compiled the most important information about the tests before and during pregnancy:

What counts for prenatal care?

The pregnancy is divided into three phases, the trimesters. On a regular basis, gynecologists use regular check-ups to monitor whether the child is well and how it develops. They also have their health in mind. A part of these statutory investigations may also be taken over by midwives. As a rule, the examinations are usually carried out monthly, and from the 32nd week of pregnancy, twice within four weeks.

Classical prenatal care includes, for example, examinations to determine the blood group affiliation and the Rhesus factor of the pregnant women. The doctor also tests for rubella and she checks the pregnant woman's urine for bacteria and the protein content. She also conducts the study on gestational diabetes, to name but a few examples.

Also provided are three ultrasound scans, which will examine how the fetus develops and whether there are abnormalities. The examinations take place approximately in the 10th, 20th and 30th week of pregnancy and are paid by the health insurance companies.

Which investigations are possible is stated in the guidelines of the Federal Committee of Physicians and Health Insurance Funds. "The primary goal of medical prenatal care is the early detection of high-risk pregnancies and high-risk births," it states.

In concrete terms, this means: "Medical care during pregnancy and after delivery should avert possible dangers to the life and health of the mother or child, as well as recognize health problems in good time and provide them with treatment."

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Where is the border with prenatal diagnosis (PND)?

Prenatal diagnostics include examinations that go much further than the preventive examinations listed on the first pages of the passport. These are found, for example, in the passport in Annex C. These procedures are about discovering possible anomalies of the embryo or the fetus. These include malformations, hereditary diseases or chromosome aberrations - a Down syndrome, for example, in which the chromosome 21 is present three times.

For example, pregnant women have been able to take advantage of extended ultrasound since 2014. In this organ screening gynecologists are looking for malformations. Which further examinations are recommended for expecting mothers, is to be decided in the individual case and in a consultation. Because not every test that can be done makes sense for all women.

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How risky are some PND methods?

For some time, there have been invasive prenatal diagnostic methods in which physicians collect genetic material from the fetus, including chorionic villus sampling, amniocentesis and chordocentesis. They are associated with some risks.

  • Chorionic villus sampling removes tissue from the placenta. The risks include infections, vascular injuries and premature labor, and it increases the likelihood of miscarriage.
  • It is similar in the case of amniocentesis , in which the amniotic sac is punctured. The examination can be performed at the end of the 15th week of pregnancy in the second trimester of pregnancy and provides information about possible chromosomal abnormalities, hereditary diseases or abnormalities in the central nervous system.
  • Chordocentesis , in which blood is taken from the umbilical cord, is considered problematic.

According to recent studies, 0.1 to 0.2 percent of all amniocentesis and less than 0.1 percent of chorionic villus biopsies have complications that may range to miscarriage. At the same time, these studies are considered to be more meaningful compared to noninvasive procedures. For example, the neck pleat measurement during ultrasound screening in the first trimester of pregnancy is among these non-limiting tests. A conspicuous finding is only a possible indication of an anomaly. On the other hand, if the combined crease measurement is inconspicuous, the examined child is not affected with a probability of 99.9 percent.

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How does the non-invasive blood test work?

This test can be performed from the first day of the 11th week of pregnancy. The doctor removes blood from the expectant mother and has her examined in the laboratory. The maternal blood contains DNA snippets of the embryo, which are first filtered out, duplicated and then analyzed. So it is possible to indirectly examine the unborn child for gene changes. For the analysis, the lab takes about two weeks (the graph shows exactly how the test works).

This procedure is therefore a non-invasive form of prenatal diagnosis, which is not associated with the risks of amniocentesis, chorionic villus sampling and chordocentesis. However, if the result of such a blood test is positive - for example, a suspected Down Syndrome - follow further investigations, for example, the already mentioned amniocentesis.

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For which pregnant women is the Down syndrome test recommended?

Pre-natal blood tests are considered a safe, but not 100% reliable method of prenatal diagnosis. Especially for all women who are older than 35 years at the time of pregnancy, they are meaningful according to recent studies. These women are by definition high-risk pregnant because they are statistically at an increased risk for certain complications during pregnancy. Also, the likelihood that the fetus has chromosomal abnormalities for chromosomes 21, 18 and 13 increases with the age of the mother.

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How meaningful are the results?

If an unborn baby has trisomy 21, it will be more than 99 percent likely to fail in a noninvasive blood test. This is not only claimed by the manufacturers, but also by the authors of the Institute for Quality and Efficiency in Health Care (IQWiG). The Federal Joint Committee had commissioned the institute to assess the usefulness of the test. Also more than 99 percent of the test in an unborn child without trisomy 21 does not hit.

The exact numbers: For trisomy 21, the so-called pooled sensitivity is 99.07 percent and the specificity 99.95 percent. In other words, the tests very rarely miss a trisomy 21, and even more seldom do they exhibit a trisomy 21 that is later confirmed.

However, these numbers should be considered with caution. Because not only pregnant women, but all pregnant women would make the blood test, according to the IQWiG report 17.4 percent of the positive test results are false-positive (50 out of 288 per 100,000 births) - so they diagnose a trisomy, although none is present. Therefore, after a positive result in the non-invasive blood test is usually tested with another method for the Down syndrome.

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Who pays a prenatal blood test so far, who the screening?

Several manufacturers in Germany have a license for the tests, with which doctors check genetic material of the unborn child in the blood of pregnant women. The examinations belong since 2012 to the individual health services (IGeL). Most pregnant women have to pay for themselves. The simplest test costs about 130 euros today. More extensive tests for various diseases cost up to 335 euros. The prices are only valid for the laboratory work, in addition to the human genetic counseling and the blood withdrawals. The prenatal diagnosticians also recommend an additional ultrasound examination of the embryo, as children's physical characteristics are more frequent than genetic factors at a ratio of 1:10.

The prenatal diagnosis as part of the Ersttrimesterscreenings, so the neck crease examination combined with a blood test, takes over the cash register usually only on request. The first-trimester screening, combined with the risk of pre-eclampsia (high blood pressure in pregnant women with water retention in the tissue), costs around 200 euros. Invasive tests such as the amniotic fluid puncture take over the health insurance, for example, in pregnant women from 35 years, because then the risk of a chromosome disorder is significantly increased, or if there is a specific suspicion of a genetic disease after another medical examination.

On request, the health insurance companies will also provide a maximum of 250 euros for the new blood test. Gynecologists are legally obliged, at least in the case of high-risk pregnancies, to point out the possibilities of prenatal diagnostic early detection.

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Why is the test probably going to pay?

Because the new blood tests offer more benefits. "We can not pretend that the application of this test is not really a medical advance in the sense of avoiding complications," the chairman of the G-BA Josef Hecken had already said in an interview in the summer of 2018. By order, the G-BA may make the decision only on the basis of the medical benefit, the necessity and the economy of the method. And the advantages are clear: The tests are superior to the previous diagnostics for trisomies 13, 18 and 21 at the end of the first trimester of pregnancy in all respects. And not only for high-risk pregnant women, to whom he is often recommended by doctors. Among other things, this has resulted in a report by IQWiG on behalf of the G-BA.

Trisomy 21 - How does Down syndrome come about? This video explains why some people have Down syndrome. One can also say trisomy 21. It shows how this happens. The video also shows how people's DNA is made up. How the cells divide. And how it happens that some people have 47 chromosomes. Not just 46 like most others. Any woman can have a baby with Down syndrome. It does not happen that often with young women. If the woman is older than 35, it happens more often. Sometimes, parents with Down syndrome get a baby. The baby may also have Down's syndrome.But that's not always the case.Only half of the babies.

Whether the test is ethically acceptable is not a question when it comes to whether or not it should become a cash benefit. Nevertheless, it is discussed on the occasion of the upcoming decision on the consequences of such tests for society. Above all is the question: who is allowed to live?

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What speaks for the cash benefit?

Proponents point out that it is fair for the health insurance companies to pay the test for pregnant women with increased risk, because then everyone can afford it. Parents who want to know if their child with a disability would be born should be able to learn this early. This is the only way for them to know if they want to receive it. In addition, the blood test allows chromosomal peculiarities such as Down's syndrome to be detected earlier during pregnancy than previous procedures. So if parents decide to cancel, it can be done sooner. Late abortions should become rarer.

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What arguments do the critics have?

Opponents of the idea of ​​turning the blood test into a health insurance fund see the right to life of disabled people threatened. In the future parents of disabled children could be asked why they did not take the test, and if they did, why they would not have finished the pregnancy then. In this way, social pressure could arise, so that people with disabilities would ultimately be taught that they have no place in society.

If the blood test leads to more abortions, critics say it will reduce the number of people with disabilities. They would be pushed into a role on the margins of society, if only because people with disabilities would be less visible in everyday life. This form of discrimination could go so far as to reduce the willingness in a society to give special support to people with disabilities in social and financial life. It should not happen that people in a society would be perceived as a burden that medical progress could have prevented.

The opponents of the blood test also emphasize that there is still a too negative picture of what life with a trisomy 21 can mean. In addition, the test result says nothing about how easy or difficult a child will be affected later. The extent of the impairment that people with Down syndrome have is broad: some graduate from high school and lead independent lives while others are severely disabled. Incidentally, this holds true for most genetic changes.

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Will the blood test lead to more abortions?

This has not been sufficiently investigated. For Germany, there are no reliable figures. Studies from Denmark indicate that abortion rates may increase and then stabilize as new prenatal diagnostic methods become available: after the country launched a more comprehensive screening program in 2004, the number of newborns with Down's syndrome decreased there In the meantime, the number of births has stabilized, Denmark now registers 23 to 35 newborns with Down's syndrome per year ( Acta Obstet., Gynecol., Scand .: Lou et al., 2017) ).

It is important to note, however, how high the proportion of fetuses with unrecognized trisomy 21 is. The IQWiG report assumes that it would not change if the blood test was only used for women in risk groups. Already today these are examined in detail. However, if in the future all pregnant women would take the test, according to the IQWiG of 100,000 births, only two children with trisomy 21 remained undetected - and thus more expectant parents would be faced with the question of whether they would like to have the child.

Initial studies from other countries, such as the US, Taiwan and the UK, have examined the impact of the introduction of the blood test. They show that the percentage of parents who decide to have an abortion after learning that their unborn child is likely to have Down syndrome does not change. In some countries, such as the US, it even appears to be decreasing ( Prenatal Diagnosis: Hill et al., 2017). However, if more parents are tested, the absolute number of abortions could still increase. Whether this is so, must show further research.

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What's next?

For example, in some countries, Belgium, the blood test for Down's syndrome is already subsidized, and in countries like Denmark it is free for high-risk pregnant women. In Germany, he will probably be a standard benefit of health insurance in the future.

Meanwhile, researchers are working on even more comprehensive, more detailed investigations. Theoretically, maternal blood could be used to detect the risk of hundreds of illnesses. Whether or not female doctors should test unborn children for diseases such as cystic fibrosis or Huntington's disease at an early stage is currently being debated intensively by medical ethicists.

One thing is for sure: with the help of genes, you can predict more than ever today. How intelligent will someone be? To which body mass index does the person tend? What about your risk for diabetes, cancer, mental illness? GPS, genome-wide polygenic scores , is the name of the tool that geneticists use to predict these and more features. And "their predictive power is improving at breakneck speed", as stated in a ZEIT article (no. 43/2018).

The gynecologist Christian Albring, president of the professional association of gynecologists, as well as the gynecologist and Pränatalmediziner Jochen Frenzel, chairman of the Saarland Association, have this article professional advice.

ZEIT ONLINE has dedicated a multimedia dossier to Trisomy 21, which you can also read in easy language.

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Source: zeit

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