Non - Invasive Rhesus Test (NIRT)
What is NIRT ?
NIRT (Non - Invasive RhesusD Test) is a simple non-invasive blood
test on blood of the pregnant women that can determine the Rhesus
D (RhD) status of your baby. This genetic test determines whether
your baby is RhD-positive or RhD-negative early in your pregnancy,
which is important for proper care for you and your baby.
What Is Rhesus D ?
Everybody has different proteins on the surface of red blood cells blood types, called
blood types. Blood type A, B, AB are well known, but there exist many more. Blood
type D, also called Rhesus (Rh), is another blood type. Most people are RhD-positive.
Others do not have the RhD protein on their red blood cells, and are RhD-negative.
The RhD-negative blood group is found in 15% of Western European people from
Belgium and The Netherlands.
When does RhD cause problems ?
RhD incompatibility in pregnancy occurs when the mother is negative for RhD and the
baby is positive for RhD. This can only occur when the father is RhD positive.
An RhD-negative mother has about a 60% chance of having an RhD-positive baby if
the father is RhD-positive. Women who are RhD-negative and have once had any of
the following instances are at risk of sensitization:
• A miscarriage
• Amniocentesis
• An induced abortion
• Chorionic villus sampling (CVS)
• An ectopic pregnancy
• Bleeding during pregnancy
• A blood transfusion
During pregnancy, certainly when any of the abovementioned instances occur, the
baby’s blood cells might enter the mother’s bloodstream causing the mother to
produce antibodies that destroy and eliminate the baby’s red blood cells. This
immune response may lead to RhD disease in the fetus and later the newborn.
RhD-negative mothers have a 1%–2% risk of being sensitized during the last
trimester of pregnancy. At delivery, the RhD-negative mother has a 10%–15% risk of
RhD sensitization.
Non - Invasive Rhesus Test (NIRT)
Sensitizing is not usually harmful if it is your first pregnancy. But problems arise when
the mother become pregnant again with another RhD-positive baby. On these
occasions the immune system ‘remembers’ how to remove these foreign blood cells
and produces lots of the same antibodies very quickly. These can enter the baby’s
blood system and damage its blood cells.
When the baby’s blood cells are attacked, it can cause anaemia. If the anaemia
becomes severe, it can lead to life-threatening problems for your baby, such as heart
failure and fluid retention.
After the baby is born, your baby’s liver won’t be able to cope with the volume of blood
cells that need breaking down. The baby may then become jaundiced, which is called
hemolytic disease of the fetus and newborn. In severe cases, this can cause
permanent brain damage and neurological problems in your baby, such as cerebral
palsy, and physical or speech problems.
Who should have a NIRT ?
If you are RhD-negative and the father is RhD-positive there exists a 60% chance of
having an RhD-positive baby, and NIRT should be performed. In certain countries
every RhD-negative woman gets a NIRT around week 27 of the pregnancy,
irrespective of the RH status of the male partner.
Non - Invasive Rhesus Test (NIRT)
When can you perform NIRT ?
This test can be performed throughout the whole pregnancy as early as gestation
week 10.
Why is NIRT important ?
If you are sensitized in a previous pregnancy, prenatal determination of RhD status is
clinically useful because no further testing or therapeutic procedures will be
necessary if the fetus is RhD-negative. If the fetus is RhD-positive, further studies will
be necessary to determine the level of fetal hemolysis (e.g., by amniocentesis,
ultrasound fetal blood sampling).
Also in a first pregnancy , NIRT might be useful. If you are RhD-negative and NIRT
indicates that you are carrying a RhD-positive fetus, your doctor may give you two Rh
immune-globulin injections, one at 28 weeks and a second within 72 hours after birth,
which will help to prevent you from developing the damaging RhD antibodies.
Which blood sample is needed ?
At least 10 ml blood in specific Streck blood tubes provided by GENDIA is required
from the mother. The maternal blood can be taken from week 10 of the pregnancy.
The sample has to be sent by Express mail to GENDIA's lab in Antwerp, Belgium, and
arrive there within 2 days of withdrawal.
How is NIRT performed in the lab ?
DNA isolated from maternal blood, which contains fetal DNA, is analyzed to
determine the presence of fetal RH.
How long does NIRT take ?
NIRT takes approximately 2 weeks to complete from arrival of the sample at GENDIA.
How reliable is NIRT ?
The reliability of NIRT is very high (> 99 %).
What is the price for NIRT ?
NIRT costs 290 Euros (everything included).