The triple test (also called a 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 testing in which the based Concentration of three hormones in the blood of the pregnant woman tries to draw conclusions about special features in the unborn child.
Time of examination
According to the guideline of a German consensus conference, the triple test should be carried out between the 15th and 18th week of pregnancy (14 + 0 to 17 + 6) and only in exceptional cases up to the 20th week of pregnancy (19 + 6). The triple test is not a routine examination and has never officially been paid for by health insurers . Since 1998, the health insurances have strictly considered this examination as a so-called "individual health service" (IGeL), the costs of which are to be borne entirely by the patients.
The attending physician is obliged to advise the pregnant woman in detail before the examination and to discuss the advantages and disadvantages in an understandable manner. This also includes the indication that no diagnoses are possible through the examination alone, but that further, sometimes invasive ones would have to follow in case of suspicion in order to obtain a diagnosis.
What is being investigated?
The triple test involves a blood test of the expectant mother .
The concentration of three substances is determined:
- α 1 -Fetoprotein (AFP)
- free estriol (uE3 from unconjugated estriol )
- chorionic gonadotropin (β-hCG) free β chain .
- If, in addition to the triple test, the value of inhibin A (InhA / folliculostatin / X-hormone) is also determined and evaluated, it is referred to as a quadruple test .
The measured concentrations of the substances are evaluated in the computer. The determined values are often given in MoM, hence the term MoM test as a synonym for triple test. The MoM value indicates how many times the respective value is higher or lower than the median value.
Taking into account the maternal age, the body weight of the pregnant woman, previous pregnancies with a child with chromosomal aberrations and the exact duration of pregnancy ( gestational age / gestational age ) at the time of the blood sample, an average probability of Down syndrome (trisomy 21) in the infant is calculated.
In some pregnant women who are expecting a child with Down syndrome, the values for alpha-1-fetoprotein and E3 are decreased, while they are increased for β-hCG.
In addition to a chromosome peculiarity, significant increases in values can also indicate a multiple pregnancy or complications such as B. moles or a chorionic carcinoma , which have nothing to do with the embryo .
The Alpha-1-fetoprotein is from entodermal formed tissues of the unborn child. A significantly increased alpha-1-fetoprotein concentration can indicate an open malformation of the abdominal wall (e.g. an abdominal cleft ) or the neural tube ( neural tube defects such as a spina bifida aperta or anencephaly ), since these are features of the alpha-1 fetoprotein gets into the amniotic fluid and through it also into the blood of the pregnant woman: In the case of neural tube malformations, for example, fetal cerebral and spinal fluid leaks into the amniotic fluid. As a result, the AFP in the amniotic fluid is increased and ultimately also passes into the pregnant woman's bloodstream in higher concentrations.
However, increased alpha-1-fetoprotein values only show such peculiarities in about two to three out of 100 cases, because increased alpha-1-fetoprotein values are also found in e.g. B. Multiple pregnancy or inaccurately specified gestational age. The measured values therefore do not allow any precise statement as to what peculiarities could be present in the child.
Influences on the result
The result of the triple test is influenced by many factors:
Often z. B. the underlying pregnancy period is not exactly. Even deviations of just one week can cause extreme fluctuations in the calculated probability.
The test certifies z. For example, an average of 100 out of 1,000 pregnant women are more likely to have their child with Down syndrome . Of these 100 women, only one actually expects a child with this chromosomal peculiarity.
An average of 40 out of 1,000 women have an increased probability of having a child with a neural tube malformation . In fact, only two of these 40 women are expecting a child with spina bifida aperta , even fewer with anencephaly .
The test is used to identify those pregnant women who have a statistically higher probability of expecting a child with a chromosomal peculiarity or a neural tube malformation , so that further diagnostics can be specifically recommended to them, because the triple test is only about an addiction test rather than a diagnostic exam. Because of this, some of the children with a corresponding peculiarity are not recognized (residual risk due to a false negative result) and the test often gives false prognoses ( false positive result).
The test provides an individual probability statement based on statistics , the informative value of which would have to be clarified by an invasive examination (e.g. chorionic villus sampling or amniocentesis ) if chromosome peculiarities are suspected . Because chromosomal peculiarities can only be diagnosed with a high degree of certainty through a chromosome analysis .
If physical abnormalities are suspected, a clarification can usually be carried out using fine ultrasound - or 3D ultrasound - or 4D ultrasound examinations, which are safe for mother and child according to current knowledge .
- Prenatal diagnostics