Fetal DNA: what it is and what it is used for

When you find out that you are pregnant, it begins for the woman one of the most beautiful experiences of her life. This period, however, is also full of questions that your OB/GYN can answer with useful information and advice. As for the prenatal tests to be performed, the choice may fall on noninvasive screening tests, such as fetal DNA testing, or invasive prenatal diagnostic tests, such as amniocentesis.

Prenatal diagnostic exams, such as amniocentesis and villocentesis, are invasive tests

Prenatal tests can find out if the baby has chromosomal abnormalities, such as Down syndrome. Prenatal diagnostic tests, such as amniocentesis and villocentesis, are invasive tests and therefore carry a risk of miscarriage, but they lead to a definite diagnosis. Usually performed only if there are predisposing factors for the presence of abnormalities in the fetus.

Prenatal screening tests, such as the Bi-test, Tri-test and fetal DNA test, offer results expressed in probabilistic terms, that is, they indicate the likelihood that the fetus is affected by a genetic abnormality’a genetic abnormality.

Fetal DNA testing is a state-of-the-art prenatal screening test. It is performed through a simple blood draw of the pregnant woman, which will be used to search for and analyze the circulating cell-free fetal DNA (cffDNA) present in maternal blood. Fetal DNA found in maternal blood originates from the trophoblast, embryonic tissue that gives rise to the placenta. During pregnancy, some small particles of the placenta may detach and end up in the maternal bloodstream.

Therefore, it is possible to find fetal DNA fragments in maternal blood.

About 11-13% of the DNA in maternal blood has fetal origin1,2.

There are several studies that have shown that fetal DNA in maternal blood is present as early as the fifth week of gestation3. Obviously, as the months of gestation progress, the amount of detectable fragments tends to increase. After delivery, however, it begins to decrease until it is no longer detectable3.

Fetal DNA fragments are smaller in size than maternal DNA fragments, so they are easily recognized1,2.

After being separated from the maternal blood and DNA, the cffDNA is sequenced. The main sequencing techniques to perform these analyses are: massively parallel shotgun sequencing (MPSS), targeted massive parallel sequencing (t-MPS), single nucleotide polymorphism (SNP) analysis4. These are state-of-the-art techniques that are performed in state-of-the-art molecular biology laboratories d’s.

With sequencing, DNA sequences are obtained that are analyzed by doctors and biologists in order to look for possible genetic and chromosomal alterations, such as trisomies 13, 18 and 21. Using fetal DNA testing, fetal sague Rh factor and the sex of the baby can also be discovered3,5.

Pregnant women can choose to have fetal DNA testing starting from the 10th week of pregnancy

This is definitely an advantage in being able to get information about your child’s health early on. Fetal DNA testing achieves more than 99% reliability in detecting trisomy 21 cases, with a higher predictive value and lower false-positive rate than Bi-test and Tri-test.

Your OB/GYN can help you plan the best course of screening or prenatal diagnosis.