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Until recently, the methods of detecting Down’s syndrome in the fetus available in Poland were either safe or effective, says Dr. Monika Jurkowska, a specialist in laboratory medical genetics. Currently, the development of medicine and genetics enables non-invasive and giving a reliable prenatal diagnosis.
– The risk of having a child with Down syndrome increases with the age of the mother – says gynecologist Dr. Piotr Węgrzyn from the Polish Gynecological Society. Testing for this defect is recommended for women over 35 years of age and for those whose biochemical and ultrasound results in the first and second trimesters of pregnancy suggest a high risk of genetic defects in the fetus. Gynecologists also recommend such diagnostics to women who underwent in vitro fertilization, those who miscarried several times, had previously given birth to a child with Down’s syndrome, had an organ transplant, blood transfusion less than 6 months before pregnancy or stem cell therapy.
Down’s disease
Down syndrome is a series of birth defects caused by the presence of extra copies of chromosome 21. A child with Down syndrome is born with one pregnancy in about 700. Children afflicted with this disease not only have lower cognitive abilities, but also an increased risk of: urinary and skeletal defects, heart, digestive system (duodenal stenosis or atresia or rectal obstruction). Heart defects are the most common cause of death in people with Down’s syndrome in early childhood. Patients are particularly prone to infections, and often develop thyroid disease and leukemia. In the UK and Germany, only one in ten mothers choose to give birth to an affected child. In Spain, an abortion ends in 96 percent of cases. There are no precise data in Poland.
Diagnostics either safe or effective
– Until recently, the methods of detecting Down’s syndrome in the fetus available in Poland were either safe or effective – says Dr. Monika Jurkowska, a specialist in laboratory medical genetics. Screening tests are offered to women at high risk early in pregnancy to rule out genetic defect syndromes. These include the PAPP-A test and the Beta-hCG test. They are perfectly safe for the fetus, but the detection rate is around 60-80% with 5% false-positive results. – This means that 5% of women will get a false positive result and will do further invasive tests, putting a healthy pregnancy at risk – says Dr. Jurkowska. Meanwhile, the invasive method of prenatal testing – amniocentesis is associated with a 1-2% risk of pregnancy loss. However, its effectiveness is 99,9%. Amniocentesis involves the insertion of a thin needle through the abdominal wall under ultrasound guidance, which extracts a small amount of amniotic fluid from the uterine cavity. The collected cells are used to test for the detection of Down syndrome and other chromosomal disorders, as well as numerous defects in individual genes. Most of the women undergoing this diagnosis feel nothing but a mild spasm. Rarely, there is slight vaginal bleeding or leakage of amniotic fluid.
A breakthrough discovery
In the 90s, it was discovered that fetal DNA passes into the mother’s blood and circulates in her plasma. It appears early in pregnancy and is detectable from the fourth week on. Thanks to this discovery, it was possible to start examining the mother’s blood and diagnosing the genetic defects of the fetus. Several centers around the world have introduced methods for the detection of genetic diseases based on the examination of free fetal DNA in the mother’s plasma. One of them is the NIFTY test available in Poland, performed on the basis of a blood sample taken from the mother. The sensitivity of the test in detecting Down’s syndrome exceeds 99% with 1% false-positive results. – I am convinced that it is only a matter of time before this research is extended to detect other genetic diseases already at this stage of a child’s development – says Dr. Anna Boguszewska-Chachulska, president of Genomed SA, who performs such tests.
Test dilemmas
Recent data show that the availability of new non-invasive diagnostic methods, contrary to initial concerns, does not increase the frequency of termination of pregnancy. – Perhaps it is related to the fact that, in the situation where only invasive tests were available, mainly women who decided to terminate the pregnancy in case of a positive result underwent it – believes Dr. Lech Dudarewicz from the Department of Genetics of the Polish Mother’s Health Center in Łódź. An abnormal NIFTY test result requires confirmation by an invasive method. – Thanks to the accuracy of the test, 100 times fewer women will face the dilemma of whether to perform invasive tests – says Dr. Monika Jurkowska. The only disadvantage of the method is its price – about PLN 2500. In Poland, the test is performed by about 120 gynecological clinics and practices.
Tekst: Halina of Pilon