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The triple test is a screening test that allows you to assess your baby’s risk of Down syndrome, Edwards’ syndrome and open central nervous system defects (such as spina bifida or anencephaly). Your doctor may order a triple test during the second trimester of pregnancy. What is the test and how to interpret the results?
Screening tests in pregnancy
During pregnancy, not only an ultrasound is performed. Your doctor may also order non-invasive screening tests that are performed at different stages of pregnancy. In the first trimester, a double test and the PAPP-A test are recommended, as well as the NIFTY or Harmony tests that show high reliability. In the second trimester of pregnancy, the emphasis is instead on the triple test and the SANCO test.
- Find out more about the double test performed in the first trimester of pregnancy.
What is the triple test?
It is not a mandatory test, but the doctor may order it due to the presence of factors that increase the risk of birth defects in the child. The triple test is performed between 14 and 20 weeks of pregnancy. After blood is drawn from a vein, the level of three parameters is determined: alpha-fetoprotein (AFP), total chorionic gonadotropin (HCG) and free estriol (fE3).
AFP concentration, i.e. fetal protein formed in the gallbladder, may indicate malformations, including nervous system abnormalities, meningeal hernia, anencephaly, spina bifida, gastroenteritis. Inappropriate levels of alpha-fetoprotein in a pregnant woman are associated with a life-threatening condition and Down syndrome. It also happens that high AFP indicates a multiple pregnancy.
Chorionic Gonadotrophin (HCG) is a hormone produced by the embryo and the placenta during pregnancy. This is one of the indicators of your risk of miscarriage. In combination with AFP and fE3, it allows the identification of Down syndrome (high HCG) or Edwards syndrome (low HCG).
The final factor in the triple test is free estriol (fE3), a steroid hormone. In the context of pregnancy, its low level is worrying.
Triple test – indications
Although the triple test can be performed prophylactically, it is most often performed for specific indications. Doctors recommend prenatal diagnosis in the form of a triple test to women over 35 years of age, in the case of birth defects in previous pregnancies, when the results of imaging or biochemical tests are abnormal. The triple test is also important in the case of congenital abnormalities in the family or chromosomal changes in the mother or father of the child. An increased risk of abnormalities also appears in the case of treating a pregnant woman in the early stage of pregnancy with antibiotics, chemotherapy, ionizing radiation or drugs for epilepsy.
If you missed the PAPP-A test between 10 and 14 weeks of pregnancy, you can do the triple test instead.
How to prepare for the test?
You do not need to prepare for the examination in any particular way. Blood can be drawn at any time of the day and also regardless of food and fluid consumption. In the case of a medical recommendation, a referral turns out to be required to perform the test. In the case of a private study, it is necessary to pay a fee, which in the case of a triple test is approximately PLN 250-400.
How to interpret the results?
Not all defects of the fetus are revealed in the form positive triple test. Moreover, only a small number of women who test positive give birth to children with Down’s syndrome, Edwards’ syndrome or a neural tube defect. That is why the interpretation of the result is performed by the doctor, who also takes into account the information obtained during the interview with the patient and the results of other tests or imaging studies.
Interpretation of the triple test results:
• in Down’s syndrome there is a decrease in the concentrations of AFP and uE3 and an increase in the level of HCG,
• in Edwards’ syndrome there is a decrease in the levels of AFP, uE3 and HCG.
However, an increased level of AFP is also observed in normal multiple (e.g. twin) pregnancies. The risk of having a baby with Down syndrome increases with the age of the mother. About 30 percent. of women around the age of 35, the triple test result may be positive precisely because of the very high risk associated with the age of the pregnant woman.
It must be remembered that the result of the triple test depends largely on the accurate assessment of the pregnancy age. If it is incorrectly identified at the beginning of pregnancy, the test results may be unjustifiably overstated or underestimated. Therefore, the interpretation of the test results should be made by an expert – geneticist or doctor who has experience in this matter.
If the result is positive, to confirm the diagnosis, the doctor may order more detailed tests – ultrasound and possibly amniocentesis. It is worth being aware that amniocentesis is an invasive prenatal test with a risk of complications of several percent. This group of studies also includes chorionic villus sampling and cordocentesis.
What else should you know?
The sensitivity of the triple test in detecting Down’s syndrome is 66%, and for Edwards’ syndrome – 60%. (This means that the test detects 6 out of 10 sick fetuses). When detecting these two syndromes, the sensitivity of the test depends largely on the age of the mother (the number of false positives increases with her age). In other words, the older a pregnant woman is, the more often she will get a false-positive result – that is, one that suggests that the fetus is sick, although in fact it is healthy. However, in the case of central nervous system defects, the age of the pregnant woman did not affect the sensitivity of the triple test.