The fetal DNA test – sometimes called a fetal DNA test, DNA test in pregnancy, or fetal DNA test – is a non-invasive prenatal test (NIPT) used to determine the risk of a fetus being born with certain genetic abnormalities.
Fetal DNA analysis is considered a non-invasive test because it only requires a blood sample from the pregnant woman and poses no risk to the fetus. In addition, NIPT is a screening test, which means that it will not give a 100% sure answer on whether or not the fetus has a genetic disease but only allows to estimate its risk.
What fetal DNA testing is and how it works
The fetal DNA test is a non-invasive prenatal diagnostic test that consists of a maternal blood sample during pregnancy. It is used to detect early the risk of the fetus being affected by chromosomal abnormalities such as Down syndrome (trisomy 21, caused by an extra chromosome 21), trisomy 18 (caused by an extra chromosome 18), trisomy 13 (caused by an extra chromosome 13) and extra or missing copies of the X chromosome and Y chromosome (the sex chromosomes). The accuracy of the test varies according to the disorder.
DNA sampling in pregnancy: who, how and when should do it (at what week)
This test analyzes small fragments of DNA that circulate in the blood of a pregnant woman. During this time, the mother’s bloodstream contains a mix of DNA that comes from her cells and placental cells. DNA in placental cells is usually identical to fetal DNA. The analysis of fetal DNA – or rather fetal free DNA (cfDNA) in maternal plasma – offers an opportunity for early detection of certain genetic abnormalities without harming the fetus.
The prenatal test requires a single blood sample and can be performed from the 10th week of pregnancy, but it is advisable to wait until the 11th, when the amount of fetal DNA flowing into the maternal blood is greater and sufficient to be isolated and analyzed. The test result is usually available within 15-20 days.
The test finds its maximum indication for those future mothers to whom invasive prenatal diagnosis is not recommended, for example because they are less than 35 years old, do not have risk factors (such as abnormal screening or positive history for genetic alterations) or because, for various problems, the collection of chorionic villi or amniotic fluid could cause a risk of miscarriage of more than 1% or finally because, For ethical-religious reasons, the risk of abortion of 1% of invasive examinations is not acceptable.
Prenatal DNA sampling, what you see
Thanks to a sophisticated system of molecular genetics, the so-called selective sequencing is carried out, that is, the arrangement of nucleotides is observed which, with their alternation, determine the characteristics of the DNA of each of us.
Fetal DNA analysis, results
By investigating the 4 pairs of chromosomes, the analysis allows to identify the chromosomal abnormalities that concern them, namely trisomy 21 or Down syndrome, trisomy 18 or Edwards syndrome, trisomy 13 or Patau syndrome and sex chromosomopathies (Turner for the female and Klinefelter for the male): all these, overall, They cover 95% of chromosomal pathologies.
In some cases, fetal DNA test results indicate an increased risk of a genetic abnormality when the fetus is actually unaffected (false positive), or the results indicate a reduced risk of a genetic abnormality when the fetus is actually affected (false negative). The reliability of the test is 99%, so it is almost comparable to that of chorionic villus sampling and amniocentesis.
If the fetal DNA test is carried out early (at 10, 11 weeks) and should be positive, a chorionic villus sampling or amniocentesis is generally recommended to be sure of the diagnosis.
In any case, the results of a fetal DNA test must always be accompanied, before and after the result, by careful genetic and family counseling. The test must also be preceded by a thorough ultrasound control of the fetus and the evaluation of some biochemical markers on maternal blood.
Cost of the test
The fetal DNA test is not yet provided for by the current Essential Levels of Care (LEA) of the National Health Service because not all the national territory has laboratories able to guarantee its execution to the entire population.
Given the great importance of this screening, we expect fetal DNA testing to become part of the New LEAs (Essential Levels of Care) so that it becomes free and free of charge for all pregnant women.
Fetal DNA test, conclusions
The fetal DNA test is an innovative, non-invasive prenatal screening test, which is performed through a blood sample of the woman in the initial phase of pregnancy and is based on the research and analysis of fetal DNA in maternal blood
The fetal DNA test requires a single blood sample and can be performed once you reach the 10th week of gestation. Collecting a maternal blood sample for DNA analysis does not pose a threat to the fetus.
If this DNA analysis indicates an increased likelihood of a chromosomal condition, a definitive diagnosis could be obtained by examining fetal cells collected with an invasive technique such as chorionic villus sampling (CVS) or amniocentesis.
Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.
She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.