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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)

  • In cases of pregnancies with fetal chromosomal defects, there will be some variations in the values of substances created by the placenta and that circulate in the maternal blood.
  • The free ß-hCG and PAPP-A are two hormones used to calculate the risk of chromosomal defects between 11 and 13 weeks of pregnancy
  • In order to obtain reliable results, it is important to use high quality equipments to calculate the amount of these two hormones. In order to be able to analyze maternal biochemistry an initial accreditation and continuous quality evaluation is also required.
  • The values obtained can vary with some maternal characteristics (weight, ethnic group, smoking), multiple pregnancies, method of conception (natural or in vitro fertilization). Subsequently, in order to calculate the risk, which is done using a software provided to only accredited professionals, taking all of these factors into account becomes essential.

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)


    Sensibility ( FMF 2010)


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.






Free ß-hCG

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.


Last Edit: 05/08/2013 8:17pm