Fetal DNA testing is an advanced screening test that allows genetic material belonging to the baby to be evaluated from the mother’s blood during pregnancy. Developments in the field of molecular genetics following the genome project have enabled more effective methods to be used not only in the diagnosis of chromosomal and genetic disorders, but also in screening processes.
Today, with the increasing integration of molecular genetic studies into clinical practice and the decrease in test costs, fetal DNA tests have become an important option in pregnancy follow-up. These tests allow risk assessment for certain chromosomal disorders by analyzing placental-origin cell-free DNA fragments found in maternal blood.
What Is a Fetal DNA Test?
A fetal DNA test is a genetic screening test performed using a blood sample taken from the expectant mother. In this test, cell-free DNA fragments circulating in maternal blood and originating from the placenta are analyzed.
The purpose of the test is to assess the risk of certain chromosomal disorders during pregnancy. A fetal DNA test is not a diagnostic test; in other words, it does not provide a definitive diagnosis on its own. However, because it has high sensitivity, it differs from conventional screening tests and may reduce the need for invasive diagnostic methods in many cases.
For Which Conditions Does a Fetal DNA Test Calculate Risk?
Fetal DNA tests can assess risk for the most common chromosomal disorders. With these tests, especially certain trisomies and sex chromosome abnormalities can be screened.
The main conditions for which risk can be calculated with fetal DNA testing include:
- Down Syndrome / Trisomy 21
- Edwards Syndrome / Trisomy 18
- Patau Syndrome / Trisomy 13
- Sex chromosome X/Y abnormalities
- Triploidy
- Certain deletion syndromes
Although these tests have high sensitivity, they do not replace definitive diagnosis. If a high-risk result is obtained, evaluation with diagnostic tests such as CVS or amniocentesis may be required.
Can Deletion Syndromes Be Screened with a Fetal DNA Test?
Risk assessment can also be performed with fetal DNA testing for certain deletion syndromes that are not included in traditional screening programs and may not always show clear findings on ultrasound examination.
Some deletion syndromes that can be evaluated with fetal DNA testing include:
- DiGeorge syndrome
- 1p36 deletion syndrome
- Angelman syndrome
- Prader-Willi syndrome
- Cri du Chat syndrome
These syndromes may not always present ultrasound findings. Therefore, fetal DNA testing may offer families a broader risk assessment in certain situations.
Is a Fetal DNA Test a Diagnostic Test?
A fetal DNA test is not a diagnostic test. It is a screening test. In other words, it indicates whether the baby has a low or high risk for certain chromosomal disorders.
Since it is not a diagnostic test, if a high-risk result is detected on fetal DNA testing, additional evaluation is required for a definitive diagnosis. In this case, CVS or amniocentesis may be recommended by the doctor.
The most important difference between fetal DNA testing and conventional screening tests is its very high sensitivity. Therefore, it may help reduce unnecessary CVS or amniocentesis procedures. As a result, the risk of pregnancy loss related to invasive procedures in normal pregnancies may also be significantly reduced.
Which Tests Are Used for Definitive Diagnosis?
If a definitive diagnosis is considered for chromosomal disorders, CVS or amniocentesis is preferred. Since these tests allow direct examination of genetic material belonging to the baby, they have diagnostic value.
However, CVS and amniocentesis are invasive procedures. Therefore, the risk of pregnancy loss should be taken into account. The risk rate stated in the text is approximately 1/500. This decision should be evaluated jointly by the family and the physician.
Screening Options According to Gestational Week
There are different options according to gestational week for evaluating chromosomal disorders. Families should choose the most appropriate option for their situation together with their doctors.
Perinatal Examination and Combined Test at 11–14 Weeks of Pregnancy
A perinatal examination may be performed between the 11th and 14th weeks of pregnancy. During this period, risk assessment is performed with PAPP-A and beta-hCG blood tests.
If the risk is found to be higher than 1/2500, fetal DNA testing may be recommended. In this approach, conventional screening is performed first, and if considered necessary, a more advanced risk assessment is provided with fetal DNA testing.
Perinatal Examination and Fetal DNA Test at 11–14 Weeks of Pregnancy
Another option is to perform fetal DNA testing directly together with perinatal examination between the 11th and 14th weeks of pregnancy. This method allows a high-sensitivity screening to be performed at an earlier stage.
Especially in cases of a family history of genetic disease, advanced maternal age, or a desire for a more detailed evaluation regarding screening tests, this option may be brought up by the doctor.
Quadruple Test and Fetal DNA Test at 15–21 Weeks of Pregnancy
If the 11–14-week examination period has been missed, a perinatal examination and quadruple blood test may be performed between the 15th and 21st weeks of pregnancy.
If the risk is found to be higher than 1/2500 as a result of this test, fetal DNA testing may be considered. In this way, risk analysis for chromosomal disorders can also be performed during the second trimester.
Perinatal Examination and Fetal DNA Test at 15–21 Weeks of Pregnancy
Another option during this period is to perform fetal DNA testing directly together with perinatal examination. Fetal DNA testing may be considered especially when a screening method with higher sensitivity is preferred instead of conventional screening tests.
Why Is Fetal DNA Testing Important?
Fetal DNA testing helps evaluate certain chromosomal disorders at an early stage during pregnancy. Although it is not a diagnostic test, it may provide families with a clearer risk assessment thanks to its high sensitivity.
One of the most important advantages of this test is that it can be performed from maternal blood without requiring an invasive procedure. Thus, the need for diagnostic tests such as CVS or amniocentesis may decrease in many pregnancies.
However, fetal DNA testing does not provide definitive results for every disease. Therefore, the test result should be evaluated together with ultrasound findings, maternal age, gestational week, family history, and other screening tests.
How Is the Appropriate Test Chosen?
The genetic screening process during pregnancy should be planned individually. The most appropriate approach may not be the same for every family. Some families may prefer to proceed first with conventional screening tests, while others may choose fetal DNA testing directly. For families seeking a definitive diagnosis, CVS or amniocentesis may be considered.
When making this decision, the following factors should be evaluated together:
- Gestational week
- Maternal age
- Ultrasound findings
- Previous pregnancy history
- Family history of genetic disease
- Results of screening tests
- The family’s expectations and priorities in the decision-making process
Fetal DNA testing is a strong screening option for evaluating genetic risks during pregnancy. However, the correct test selection should always be made through perinatal evaluation and physician recommendation.
Frequently Asked Questions
What is a fetal DNA test?
A fetal DNA test is a genetic screening test performed by examining placental-origin cell-free DNA fragments found in maternal blood.
Does a fetal DNA test provide a definitive diagnosis?
No. A fetal DNA test is not a diagnostic test; it is a screening test. In high-risk results, CVS or amniocentesis may be required for definitive diagnosis.
Which conditions does a fetal DNA test screen for?
Risk assessment may be performed for Down syndrome, Edwards syndrome, Patau syndrome, sex chromosome abnormalities, triploidy, and certain deletion syndromes.
When is a fetal DNA test performed?
It can generally be considered from the 11th week of pregnancy onward. However, the most appropriate timing should be determined according to gestational week and the doctor’s evaluation.
Can fetal DNA testing be performed instead of amniocentesis?
Fetal DNA testing may reduce the need for amniocentesis in many cases. However, when a definitive diagnosis is required, amniocentesis or CVS may still be necessary.