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Positive blood test beta/Papp A

The test’s positive result is due to the blood test (duotest/dualtest/bitest/ integrated test /ultrascreen)

  • In pregnancies with a fetus affected by chromosomal defects, it is possible to detect some substances produced by the placenta in the maternal blood.
  • The Free ßeta-hCG and PAPP-A  are two hormones, which are also used at 11-13 weeks, for the calculation of chromosomal defects.
  • The values obtained will depend on conditions of the mother (weight, ethnic group, smoking), from the number of fetuses’ present and mode of conception (natural or IVF). Subsequently, when calculating risk, these factors will have to be taken into account. This is made possible by the software, which is supplied to the certified practitioner and the final report will include the values of these factors.


Variations in the distribution of FreeBeta -Hcg  in Trisomy 21

The value is provided with a number known as MoM.

For example a MoM of 4 is considered to be high (but not necessarily a sign that there are problems!). The absolute value defined by the laboratory (for example  PAPP-A 2,930 mlU/ml) by itself doesn’t not indicate anything. It is dependent on many other variables (gestational age, weight, etc..), that only the software is able to analyze and translate into a useful data. This data is known as MoM (multiples of the median)


Variations in the distribution of Free B-HCG  in Trisomy 21


 Variations in the distribution of PAPP-A  in Trisomy 21


Based on the values of the specimen, it is possible to have an indication on which kind of chromosomal abnormality to test for.

In cases of trisomy 21, the values tend to be disassociated. One tends to be higher than the average (B-Hcg), while the other will be lower (PAPP-A)

With trisomies 13 and 18, both values will be low

It is only when the values are outside the average, especially when the PAPP-A is low (less than 3 MoM) that a doctor should consider conducting further investigation to ensure avoiding maternal predisposition to pregnancy complications in the III trimester.

To ensure that the results obtained are reliable, expertise and the use of high quality equipments remains essential.  The laboratories analyzing the serum maternal biochemistry have also to undergo a process of accreditation and continuous quality control.

The doctor performing the examination, will have to ensure that other variables (such as wrong temperature) which have the potential of altering the results have not contaminated the sample.

Last Edit: 04/05/2013 12:23pm