Triple-Test

The triple test (also referred to as the MoM test: MoM = multiples of the median, English: The multiples of the median concentration) is due to the relatively uncertain results, he brings controversial method of prenatal diagnosis, in which, on the basis of the concentration of three hormones in the blood of pregnant women attempting to draw conclusions about specific features in the unborn child.

Time of investigation

After a German guideline consensus conference of the triple test 15 to 18 weeks gestation should be performed (14 0 to 17 6) and only in exceptional cases up to 20 weeks of gestation (19 6). The triple test is not a routine examination and was never officially paid by the health insurance. Since 1998, health insurance companies consider this study stringently as so-called " individual health service " ( IHS ), the costs are complete take over of the patients.

The attending physician is required to advise the pregnant woman before the examination in detail and discuss the pros and cons in an understandable way. This includes the indication that no diagnostics are possible only by the investigation, but at a more suspicion, partly invasive should follow in order to get a diagnosis.

What is being tested?

The triple test includes an examination of the blood of the mother.

Determines the concentration of three substances:

• α1 -fetoprotein ( AFP)
• Free Estriol ( uE3 of Engl. unconjugated estriol )
• Free β - chain of chorionic gonadotropin ( β - hCG).
• If, in addition to the triple test, the value of inhibin A ( InhA / Follikulostatin / X - hormone) also determined and evaluated, one speaks of the quadruple test.

The measured concentrations of the substances to be evaluated in the computer. The determined values ​​are often given in MoM, hence the name MoM test as a synonym for triple test. The MoM value indicates to the Wievielfache the respective value is higher or lower than the average value.

Evaluation

Taking into account maternal age, body weight of the pregnant woman, previous pregnancies with a child with chromosome aberration and the exact duration of pregnancy ( gestational age / gestational age ) at the time of blood collection ( trisomy 21 ) is calculated in the infant, inter alia, an average probability of Down syndrome.

Some pregnant women who are expecting a child with Down syndrome, the values ​​for alpha 1- fetoprotein and E3 are reduced for β -hCG are elevated, however.

In pregnancies with a child with Edwards syndrome ( trisomy 18) is frequently reduced levels of AFP, hCG and estriol find; the AFP level is often below 60 % of the normal median.

Significant Increases in addition to one chromosome specificity also indicate a multiple pregnancy or complications such as hydatidiform mole or chorion carcinoma who have nothing to do with the embryo.

The Alpha -1 -fetoprotein is formed from endodermal tissues of the unborn child. A significantly increased alpha -1 -fetoprotein concentration may on an open malformation of the abdominal wall (such as a stomach column) or the neural tube ( neural tube defects anencephaly as spina bifida or ) point, as these features, the Alpha-1 -fetoprotein into the amniotic fluid and above also enters the blood of pregnant women: in Neuralrohrfehlbildungen example, it comes to the exit of the fetal brain and spinal fluid in the amniotic fluid. Thus, the AFP is elevated in the amniotic fluid and eventually goes in increased concentration in the bloodstream of pregnant women about.

However, show increased alpha -1 -fetoprotein values ​​only in about two to three cases out of 100 such special features in the child, because elevated alpha -1 -fetoprotein values ​​are also in, for example, multiple pregnancy or inaccurate specified gestational ages ago ( gestational age ). Therefore, the measured values ​​do not allow for precise information about which there may be special in the child.

Influences on the result

The result of the triple test is influenced by many factors:

Frequently, for example, underlying the transaction duration of pregnancy is not exact. Even deviations of only one week can already cause extreme fluctuations of the calculated probability.

For the test, for example an average of 100 of 1,000 pregnant women certifies an increased probability that their child has Down syndrome. Of these 100 women but then, just a fact a child with this chromosomal specificity.

On average, 40 of every 1,000 women an increased probability of a child with a Neuralrohrfehlbildung is certified. In fact, only two of these 40 women expecting a child with spina bifida, anencephaly with it are even less.

Criticism

The test is used to identify those pregnant women who have a statistically increased likelihood to expect a child with a chromosomal or a special Neuralrohrfehlbildung, so give them a further diagnostics may be recommended specifically because it is the triple test only to a screening test and not a diagnostic test. As a result, some of the children will be with a corresponding specificity not detected ( residual risk through a false negative result ) and the test gives many false predictions ( false positive result ).

The test entails a statistics -based individual probability indication, whose significance, if necessary, in case of presumed chromosome specificity by an invasive investigation (eg, chorionic villus sampling or amniocentesis ) should be clarified. Only through chromosome analysis can be chromosomal features with high reliability diagnose.

When suspecting a physical abnormality clarification can mostly through according to current knowledge for both mother and child carried hazardous fine ultrasound or by 3D ultrasound or 4D ultrasounds.