In Estonia, a combined screening is used to detect the risk of chromosomal diseases prenatally. The screening helps find foetuses with an elevated risk from thousands of pregnant women and then suggests additional genetic analyses. These analyses are reimbursed by the Estonian Health Fund. In the combined screening, the level of certain biomarkers in maternal blood serum is determined, the foetus is examined by ultrasound and pregnancy related risk factors are taken into account. That is all done without interfering with the foetal environment. For this reason, the combined screening is known as non-invasive and it is safe for the foetus.
The screening determines pregnant women with an elevated risk of having a baby with chromosomal disease. In case of high risk, the women are advised to confirm the diagnosis via an invasive analysis (diagnostic foetal chromosomal analysis). This is the most precise analysis that involves an invasive procedure (amniocentesis, chorion villus biopsy or cordocentesis) to get a sample of foetal DNA. In an invasive test, the foetal DNA is taken from either amniotic fluid or placenta. However, invasive procedures may cause miscarriage in 1% of cases.
Invasive procedures pose a small but definite risk of miscarriage (up to 1%). More than 600 invasive procedures are done in Estonia annually. Currently, the used screening tests help find 80-96% of foetuses with chromosomal diseases. The false-positive rate (the screening detects elevated risk, but the foetus is well) is 2-10%. These women go though invasive procedures to confirm that the foetus does not have a chromosomal disease. More than 90% of women that go through invasive procedures receive the answer that the foetus is well. That means that the stress, spent time and money have been in vain.
12-23% of the screening results are false-negative. This means that a foetus with chromosomal disease is not found during pregnancy. Non-detection of chromosomal disease during screening is one of the main reasons why a woman becomes aware of a child’s illness at only the third trimester.
Despite the fact that pre-natal screening has been organised in Estonia in the best possible way, current methods are not able to ensure the flawless testing of foetuses. A major drawback is the lack of precision of the screening methods in use. Therefore, it is important to apply a modern and significantly more advanced NIPT method that detects the possible additional chromosome of the foetus directly from the mother’s blood sample.
What is the result of testing?
The graph on the right shows the numbers of prenatally detected and born babies for Down syndrome in the years 2000-2014. In Estonia, almost 100% of pregnant women take part in the screening programme. Annually, about 30 foetuses with Down syndrome are discovered. The number of babies born with Down syndrome has significantly reduced. Nevertheless, about 5 babies with Down syndrome are born in a year. Most of them have not been found in the screening.