Fetal Rh factor RhD non-invasive PCR test

General Information

The test will be sent on Friday. 

Sampling will be carried out in regional branches on Thursday.

Sample collection at Tbilisi branches will be carried out on Thursday or Friday morning.

Samples must arrive at the central laboratory by 12:00 on Friday.

What is the Rhesus factor?

Rhesus factor is a protein on the surface of red blood cells (erythrocytes), which is synthesized by the RhD gene and is inherited from our parents. Most people (83%-87%) have this protein on the surface of their erythrocytes and are called Rhesus-positive, while a small proportion (13%-17%) do not have the Rhesus protein and are called Rhesus-negative.

What is fetal RhD? Rh factor Non-invasive test?

There is a risk of Rh sensitization to RhD for an RhD-negative woman who is pregnant with an RhD-positive baby. When sensitization develops, antibodies are formed in the body of a pregnant RhD-negative woman, which can enter the blood of an RhD-positive baby through the placenta. This causes serious complications in the fetus.

Mixing of maternal and fetal blood cells sometimes occurs during childbirth, as a result of microtrauma to the placenta and umbilical cord.

Who should have fetal RhD testing? Rh factor Non-invasive test?

• Rh negative Pregnant women to determine the need for Rh prophylaxis (Rhesus prophylaxis is performed if the fetus is Rh-positive)

• Rhesus negative pregnant women Those who are sensitized with anti-D antibodies

How does the test work?

Fragments of fetal genetic material that are released from the placenta circulate in the mother's blood (extracellular DNA) during pregnancy.

Using molecular biological methods (real-time PCR), these fragments are examined for the presence of the Rhesus D gene. If the Rhesus D gene is detected in the fetus, the fetus is Rhesus positive. Only a blood sample from the pregnant woman is required for the study. The test has no negative effects on the health of either the fetus or the mother.

The sensitivity of the test exceeds >99%, and the specificity is >98%.

When is the survey conducted?

Determining the Rh factor of the fetus is recommended from the 19th week of pregnancy. The test can be performed from the 12th week of gestation, however, in case of a negative RhD result, it is necessary to confirm the result with a repeated test from the 17th week of pregnancy.

The study is conducted only on the basis of the pregnant woman's written informed consent!

Research Results

Regardless of determining the Rh factor of the fetus, it is recommended that the newborn's blood Rh factor be determined using umbilical cord blood immediately after the baby is born.

Positive result: The fetus is Rh positive, so anti-D prophylaxis is recommended.

Negative result: If the fetus is Rh negative, anti-D prophylaxis is not required. (A negative result obtained before the 19th week of pregnancy is not considered definitive).

Material for examination: Venous blood (EDTA)

Limitations

– The test is only useful for singleton pregnancies. It is not performed in twin pregnancies.
– If the test result is unclear (1%) anti-D prophylaxis should be administered
– Rare genetic variants of the Rh factor may give a false positive result, in 0.2-0.3% of cases
– A false-negative result may be due to low concentrations of free fetal DNA, degradation of fetal DNA, or hemolysis of the test sample.