When is NT performed » When the blood test be done ?
Maternal blood is analyzed to check the level of PAPPA-A and Free Beta HCG. The test is also known as: bitest /b-test/duotest/dualtest/integrated/combined/ultrascreen
THE EXAMINATION OF THE MATERNAL BLOOD COMBINED WITH NUCHAL TRANSLUCENCY (bitest/b test/duotest/dualtest/integrated test /combined test /ultrascreen)
Compared to normal pregnancies, where the fetus is positive for trisomy 21, the maternal biochemistry indicators are greater at 9 rather than 13 weeks. Subsequently, the effectiveness of the combined ultrasound and biochemistry screening is higher if the blood test is conducted earlier (9-10 weeks)
Detection rate (source FMF 2010)
If we associate the test’s higher detection rate of an earlier blood sampling to that of nuchal translucency, we can observe, as evident in the graph, an increase in general reliability
Distribution of PAPP-A in normal fetuses and those affected by Down syndrome
The level of PAPP-A appear to be almost half in cases of Down syndrome compared to normal pregnancies.
Distribution of free ß-hCG in normal fetuses and those affected by Down syndrome
There is a wide overlap in values of this substance between pregnancies with normal chromosomes (black lines) and those affected by trisomy 21 (red lines). However on average, the level of ß-hCG is almost double in cases of trisomy 21
Compared to normal pregnancies, in cases of trisomy 21, the difference in the biochemistry indicators, especially the PAPPA-A is greater at 9-10 weeks rather than at 13.
The result of these two examinations will help the medical practitioner understand and predict the kind of chromosomal abnormality (18-13), such as Turner syndrome that the fetus may carry. This is because in the values of the two hormones taken into account in the biochemistry component, the distribution will change depending on whether the fetus is normal or affected by the different trisomies.
Moreover, although it may not fully indicate a chromosomal abnormality, the examinations provide useful information on whether the pregnancy is at a higher risk for some of the major obstetric complications (pre-eclampsia, neo-natal death, pre-term delivery). It is very important that laboratory results are checked by an experienced professional.