A triple test is an assessment of the risks of whether a fetus suffers from a chromosomal abnormality or a neural tube malformation. The test does not achieve a definite diagnosis but is performed to assess whether amniocentesis should be performed, if necessary.
What is the triple test?
A triple test is an assessment of the risks of whether a fetus is suffering from a chromosomal abnormality or a neural tube malformation. The triple test is a blood test used to aid prenatal diagnosis in patients with a high-risk pregnancy. It is used to estimate whether there is an increased risk of having a child with trisomy 21, trisomy 18 (chromosomal defect) or spina bifida (open back). For this purpose, the triple test determines the concentration of the alpha-fetoprotein (AFP), the hormone estriol and the hormone human chorionic gonadotropin (hCG) in the blood of the expectant mother. The three values of the concentration in relation to the age of the pregnant woman and the health history allow a risk assessment. The resulting result is decisive about possible further examinations, such as amniocentesis (amniocentesis). The test is performed between the 14th and 18th week of pregnancy and a test result is available after only a few days. Long-term studies have shown that the risk assessment and its prognosis are often incorrect, so the triple test is now considered unreliable and is rarely performed.
Function, effect, and goals
To make a risk assessment based on a triple test, blood must be drawn from the pregnant woman. The blood is then sent to a laboratory to determine and assess the concentration of a specific protein and two hormones. The protein to be determined is the so-called alpha-fetoprotein. Within the fetus, the protein is produced in the liver, among other places, and is secreted into the amniotic fluid. If the skin of the fetus is unclosed, as in the case of spina bifida, for example, increased alpha-fetoproteins are released into the amniotic fluid and the concentration is increased accordingly. However, if the concentration of alpha-fetoprotein is below normal, this may indicate a chromosomal abnormality. A hormone is produced by the adrenal gland and liver of the fetus, which is converted to the hormone estriol within the placenta. The hormone can also be detected in the blood of the pregnant woman. In the course of pregnancy, the concentration in the blood increases. If the concentration of estriol is below the normal values, this can also be an indication of a chromosomal abnormality and the risk of the fetus suffering from trisomy 21 is increased. The third hormone assessed in the triple test is human chorionic gonadotropin, also known by the abbreviation hCG. The hCG hormone is secreted just a few days after fertilization. A pregnancy test therefore also tests the urine for the hCG hormone and a possible pregnancy can be detected or ruled out at an early stage. If the concentration is elevated in the human chorionic gonadotropin triple test, this may indicate trisomy 21 (Down syndrome). If the value is below normal, this may be an indication of trisomy 18 (Edwards syndrome). The result, which results from the concentration in the blood, is not evaluated in detail in the triple test. The age and previous illnesses of the expectant mother, as well as weight gain during pregnancy, duration and previous course of pregnancy are individually included in the overall result. Furthermore, it is important for the risk assessment whether children with a genetic defect or spina bifida have already been born to the woman or whether such diseases occur in the family history. Studies and long-term performance of a triple test have shown that the accuracy can only be classified as “medium”. By testing, about 70 out of 100 fetuses with a chromosomal abnormality or an open back are detected early. However, about 7 out of 100 are mistaken for an unborn child with trisomy 21 or trisomy 18. In general, the triple test achieves a higher accuracy in middle-aged women than in young women. Many expectant parents are unsettled by the result and may make wrong decisions.It should always be noted that the triple test does not provide a confirmed diagnosis, but only serves to assess the risk. Further examinations are necessary to make a diagnosis. For example, an amniocentesis (amniotic fluid examination) provides clarity.
Risks, side effects, and hazards
The blood draw for the triple test poses no risk to the mother or her unborn child. The real risk is based on the theory of probability that the triple test causes. The test does not make a diagnosis and this can lead to wrong decisions by the expectant parents. In addition, there are many confounding factors that can influence and falsify the result. In multiple pregnancies, the concentration of hormones and protein is basically increased. Pregnant women who smoke or eat a vegetarian or vegan diet also have an increased hCG value, despite a healthy fetus. Furthermore, an incorrect calculation of the duration of pregnancy, existing overweight and diabetes of the expectant mother can influence the result. Also a disturbed growth of the fetus, a functional disorder of the placenta and a kidney dysfunction of the pregnant woman can cause increased concentration values. The triple test can thus show deviating values even though the unborn child is healthy. If there is an increased risk, in the opinion of the treating specialist, and the expectant parents want a confirmed diagnosis, an amino-centesis should be performed. The triple test can be done ahead of time to help decide whether aminocentesis should be performed with the increased risks.
