Combined test and fetal DNA test: what they are and when to do them

Combined test and fetal DNA test: what they are and when to do them
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Combined test and fetal DNA test

During pregnancy, the woman can undergo prenatal screening of various levels, useful for identifying any chromosomal pathologies or fetal malformations. In fact, there are not only villocentesis and amniocentesis, but also ultrasounds and blood tests that can provide important information.

In particular, in this article, we talk about the so-called "combined test" and "fetal DNA test" (also called NIPT). There are still many doubts and perplexities of future mothers regarding these in-depth examinations, but we try to answer all doubts by highlighting the objective and potential of these screening tests.

In this article

Read also: Pregnancy: all the exams you can take for free

Prenatal screening tests: what they are

For several years, the prenatal investigations they have grown rich, offering new pregnant women test at screening. In addition to the classic "invasive" diagnostic tests (villocentesis and amniocentesis), there are also "non-invasive" alternatives capable of estimating the risk of some chromosomal abnormalities and highlighting any fetal malformations already in the first months of pregnancy,

It is not a question of diagnostic tests, therefore, but of screening methods. These, in detail, are the combined test and Fetal DNA test (NIPT). The first consists of two tests (an accurate ultrasound and a blood test), the second only a blood sample. But let's find out all about these two possibilities pregnant women have: 

Combined test: what it is and when to do it

The combined test, as mentioned above, is a screening test and not a prenatal diagnosis. That is, it is able to provide an estimate of the risk of any chromosomal abnormalities of the child, but without any diagnostic certainty (to have a certain diagnosis you need villocentesis and amniocentesis).

It consists of athorough ultrasound, called nuchal translucency and a blood test called bi-test.

The ultrasound examination is used to measure the nuchal translucency, which is the measurement of the collection of fluid present in a space between the skin of the nape and the vertebral column of the fetus.

On the other hand, blood sampling is useful for measuring the concentration of two pregnancy-specific substances, human chorionic beta-gonadotropin (beta-HCG) and pregnancy-associated plasma protein A (PAPP-A).

The data that emerge from the combined test are then processed by specific software in combination with other parameters such as maternal age, fetal length and gestational age. The report will not be positive or negative, but a higher or lower risk index.

The combined test should be performed between 11 and 14 weeks.

Fetal DNA test: what it is and when to do it

The Fetal DNA test (or NIPT - Non Invasive Prenatal Test) is a blood sample that is done to the expectant mother, with the aim of identifying early chromosomal abnormalities such as Trisomy 21 (Down syndrome), Trisomy 13 and Trisomy 18. Just like the combined test, it is a screening and non-diagnostic test (such as amniocentesis and CVS) that expresses an estimate of risk. 

It can be done from the 10th week of pregnancy. All women (under and over 35) can undergo the Fetal DNA test. It is a choice suggested by most gynecologists, even in the case of contraindications to invasive investigations, in pregnancies in which it is necessary to assess the risk of genetic diseases, in single and twin pregnancies. This is a paid exam. 

Combined Test and Fetal DNA Test: Risks

There is no risk to the woman and baby undergoing a Combination Test or Fetal DNA Test. These are non-invasive screening tests with no contraindications.

Since these are screening and non-diagnostic tests, however, they cannot definitively establish whether or not the fetus is affected by a particular disease, but only indicate the probability of this happening.

If the tests provide a positive result, scientific societies recommend confirming this with a traditional examination such as amniocentesis or CVS, before evaluating a possible termination of pregnancy.

Combined Test and Fetal DNA Test replace CVS and Amniocentesis

Think that the combined test and the fetal DNA test can be a substitute for CVS or amniocentesis is obviously not correct. These are completely different exams, as mentioned above, absolutely not comparable.

The first two, the ones we have talked about at length in this guide, are thorough, safe, risk-free tests for mom and baby, but not diagnostic. If you want to be sure about any fetal problems, therefore, the only solution is to resort to CVS and amniocentesis.


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