Prenatal genetics examines the health of the foetus, via screening or diagnosis of chromosomal or molecular abnormalities.
Prenatal screening for Down’s syndrome using high-throughput sequencing of freely circulating DNA
When screening freely circulating foetal DNA for Down’s syndrome, previously referred to as NIPT (non-invasive prenatal testing), the data generated from the sequencing allows screening for Down’s syndrome as well as other foetal chromosomal abnormalities. This test is based on the presence of freely circulating foetal DNA in the blood of pregnant women. The conditions for prescribing and performing this test are governed by the Decree of 14 December 2018 on the conditions for the performance of prenatal screening and diagnosis in France.
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Diagnosis of foetal chromosomal abnormalities
Rapid screening for the main types of aneuploidy from foetal samples
When taking a foetal sample (chorionic villi, amniotic fluid, foetal blood, we primarily screen for Down’s syndrome, Edward’s syndrome or Patau syndrome and sex chromosome abnormalities using a rapid technique called QF PCR (quantitative fluorescent PCR), which can give an initial rapid result in 48 hours. This result will then be confirmed using a conventional cytogenetics analysis (karyotype) or chromosomal microarray analysis (CGH array or SNP array).
Chromosomal microarray analysis (CGH array or SNP array)
In the antenatal period, if a sample of chorionic villi, amniotic fluid or foetal blood is taken, a chromosomal microarray analysis (CMA) can be conducted. It is mainly recommended when there are ultrasound warning signs. This pangenomic chromosome analysis can identify minute chromosomal imbalances that are difficult or impossible to identify using a karyotype. Gain (duplication, triplication, etc.) or loss (deletion) imbalances in the genetic material are referred to as CNVs (Copy Number Variation).
Eurofins Biomnis has SNP array (Single Nucleotide Polymorphism) technology, which in addition to being able to identify CNVs, can identify regions of loss of heterozygosity (LOH). The SNP array technique can also be used to identify triploidy, and can thus be used in the genetic study of foetal death.
Prenatal exome analysis
When fetal malformations are discovered during pregnancy, identification of a genetic cause allows to precise the prognosis of the fetal outcome and permits genetic counselling for the couple and their families.
Offered prenatally at the Eurofins Biomnis laboratory since 2022, this test analyzes all of the protein-coding regions of all identified human genes, which contain more than 95% of the known variations to date. Exome analysis can be prescribed for clinical signs strongly suggestive of gene diseases such as renal, cerebral or bone anomalies, or persistent increased nuchal translucency in the second trimester of the pregnancy. Search for fetal DNA contamination by maternal DNA is systematically carried out. This analysis allows an additional diagnosis rate compared to ACPA of 20-30% on average.
The advantages of this approach are that all genes are studied simultaneously and that the interpretation of the results can be made by integrating the most recent medical findings in the shortest possible time.
Targeted prenatal molecular testing
In cases of a family history of severe genetic diseases or concerning foetal ultrasounds, most often at the request of a CPDPN (French Multidisciplinary Centre for Prenatal Diagnosis), we offer routine screening using molecular biology for certain genetic diseases.
As such, we offer the following prenatal screening tests: fragile X syndrome, mucoviscidosis, Prader–Willi syndrome, Angelman syndrome and screening for uniparental disomy (primarily chromosomes 14 and 15).
In addition, in certain specific cases, we offer screening for specific mutations linked to a familial genetic disease using targeted Sanger sequencing.
