Can a doctor diagnose Down syndrome syndrome

Cochrane

background
Down syndrome (also known as trisomy 21) is an incurable genetic disease that causes significant physical and mental health problems and impairments. However, there is a wide range in the manifestation of Down syndrome. Some people suffer from severe impairments while others have only minor problems and can lead a largely normal life. It is not possible to predict how severely Down syndrome will affect a baby.

Expectant parents have the option of screening for Down syndrome during pregnancy to help guide their decisions. When a pregnant woman is expecting a baby with Down syndrome, a decision must be made whether to terminate or continue the pregnancy. This information enables parents to prepare for life with a child with Down syndrome.

The most reliable test methods for Down syndrome are the amniotic fluid the baby is in (amniocentesis or amniocentesis) or tissue of the placenta (chorionic biopsy (CVS)) to examine for chromosomal abnormalities that lead to Down syndrome. In both tests, needles are passed through the mother's abdominal wall, which increases the risk of miscarriage. For this reason, these examinations are not suitable for all pregnant women. Instead, other tests for Down syndrome screening are used, in which certain markers are measured in the mother's blood or urine or via ultrasound examinations of the baby. These screenings do not provide complete certainty, cases of Down syndrome can go undetected or results with high risk values ​​can result, even though the babies are not affected by Down syndrome. Therefore, in pregnancies that these tests have shown to be at high risk, an amniotic fluid test or CVS must be performed to confirm the diagnosis of Down syndrome.

Our analysis
The aim of this review was to find out which of the blood tests performed during the first three months of pregnancy are most reliable for predicting the risk of having a baby with Down syndrome. We analyzed 18 different markers in the mother's blood that can be viewed individually or in combination. The blood samples were taken before the 14th week of pregnancy. This results in 78 different screenings for the detection of Down syndrome. We found 56 studies with 204,759 pregnant women, of which 2113 pregnancies were affected by Down syndrome.


Our results
For the first 14 weeks of pregnancy, a recommendation for the so-called double test is derived from the evidence, which tests for two markers in the blood: PAPP-A (pregnancy-associated plasma protein A) and free beta-human chorionic gonadotropin ( βhCG), taking into account the age of the pregnant woman. This test will detect seven out of 10 (68%) pregnancies that have Down syndrome. Usually, women with a result suggestive of high risk are offered an amniotic fluid test or CVS. About one in 20 women (5%) who have this test will get a result that implies high risk, but in most cases the baby will not have Down syndrome. From our point of view, there is little evidence for the examinations in the first 14 weeks of pregnancy that supports the performance of serum tests for more than two markers in the blood.

Other important information
Other than the risks of a normal routine blood test, the blood tests themselves do not cause any undesirable effects in women. However, women whose blood tests indicate a high risk and who will have an amniotic fluid test or CVS performed as a result are at risk of miscarriages in healthy children. Parents must weigh this risk when deciding whether or not to have an amniotic fluid test or CVS based on high-risk blood test results.