The Haute Autorité de Santé recommends offering pregnant women, as part of screening for Down syndrome, examinations based on circulating free DNA in order to detect other chromosomal abnormalities.
- If there is a high risk of Down syndrome revealed by standard examinations, pregnant women should be offered a free circulating DNA test.
- The goal is to identify other chromosomal abnormalities.
- “Anomalies meeting these criteria are trisomies 2, 8, 9, 13, 14, 15, 16, 18, 21 and 22 and non-cryptic segmental anomalies.”
During pregnancy, an ultrasound and blood tests make it possible to assess the probability that the fetus has trisomy 21 or not. If the risk is high, a diagnosis by analysis of the fetal chromosomes following an amniocentesis , namely a sample through the stomach, is proposed. In 2018, the prenatal screening strategy for Down syndrome evolved, on the recommendations of the High Authority of Health, (HAS) to improve performance with the integration of a new test: the circulating free DNA test (flcDNA) . He “looks for an over-representation of the number of copies of chromosome 21 in the free DNA circulating in maternal blood, the latter being a mixture of fetal and maternal DNA”indicates the health authority.
Circulating free DNA tests used to detect chromosomal abnormalities other than Down syndrome
To limit the number of invasive samples, this examination based on free circulating DNA is therefore systematically offered to all future mothers. “whose combined examination of the first trimester shows a risk of Down syndrome of between 1/1000 and 1/51 instead of an immediate karyotype for women whose risk of the combined examination was greater than 1/ 250.” Problem: the introduction of this test may reduce the detection of chromosomal abnormalities due to the reduction in the number of karyotypes. This is why the HAS wanted to determine whether the free circulating DNA tests, carried out as part of screening for Down syndrome, were effective in detecting other abnormalities in the structure or number of chromosomes.
After reviewing various data from the literature on this question, the High Authority of Health has made his opinion this October 2. It recommends offering pregnant women, whose standard examinations reveal a high risk of Down syndrome, the search for chromosomal anomalies compatible with an active pregnancy and likely to lead to particularly serious fetal or obstetric consequences. “In the current state of knowledge and in view of the prevalence of fetal damage and the known consequences of placental damage, the anomalies meeting these criteria are trisomies 2, 8, 9, 13, 14, 15, 16 , 18, 21 and 22 and non-cryptic segmental anomalies.”
Free circulating DNA tests: providing reliable information to pregnant women
The health authority also recommends extending the indications for circulating free DNA tests to patients with a history of pregnancy with aneuploidy, if one of the parents carries a Robertsonian translocation involving chromosome 13 and in the case of a maternal serum marker profile. of the first trimester suggestive of trisomy 13 or 18. She also advises that information on this subject be reliable and understandable for future mothers so that they can make a considered decision about carrying out screening and diagnostic examinations.
