A blood test called the triple test is done in the second trimester of pregnancy to give an estimate of the risk of Down syndrome in the fetus.
The triple test gives the best results when done in the second trimester of pregnancy, between weeks 16 and 18, but can be done anytime after the fifteenth week up to the twenty-second week. The gynecologist who monitors the pregnancy will determine whether such a test is necessary or not. In general, it is recommended for mothers-to-be who have a higher risk of birth defects, especially trisomy 13, 18 and 21 or Down syndrome, or for those with a personal or family history of children with birth defects. It is also indicated for pregnant women over 35 years old, with diabetes, who had a viral infection during pregnancy or were exposed to high levels of radiation.
Read also: Hepatitis and pregnancy: what precautions are required
The procedure is the same as for blood tests
Like any other blood test, the triple test is done at a clinic or laboratory. The process is similar to regular blood tests. The triple test measures the amounts of 3 substances in the blood: alpha-fetoprotein, human chorionic gonadotropin and estriol. When a test for hormone A inhibition is added, it is called quad screening. The levels of these substances help the doctor find out if there is a risk that the baby will have certain birth defects, such as Down syndrome, spina bifida or anencephaly.
Read also: Blood tests necessary for pregnant women
What are the consequences of abnormal results?
If the values of the biochemical parameters in the blood are abnormal, the gynecologist will recommend an additional test, called amniocentesis. In this situation, 15-20 ml of amniotic fluid are extracted. Although abnormal results can be worrisome, they do not necessarily mean that there is anything to worry about. Instead, they are a good indication to continue testing or to make doctors more careful during pregnancy monitoring.
Risks in case of multiple pregnancy
The triple test was first performed in 1988. It is now clear that serum levels can be different in singleton and multiple pregnancies, which could lead to more unnecessary amniocentesis procedures in women with normal twin pregnancies . Thus, the levels of suspicion for each of the test components must be adjusted according to the type of pregnancy. Maternal weight and age influence the risk estimate, independent of the actual serum levels of the chemicals. Changes in maternal weight are related to many factors, including multiple pregnancy. Thus, a separate model may be required to make the test more accurate. In recent decades, more effective and non-invasive tools have been developed, which could be adopted more widely in the future.
Dr. Andreas Vythoulkas, specialist in obstetrics-gynecology, with overspecialization in infertility
This test, indicated for pregnant women under the age of 35, has the “mission” to check the maternal serum level of alpha-fetoprotein, unconjugated estradiol and human chorionic gonadotropin. If these substances are found in quantities that are too small or, on the contrary, too large, the risk of neural tube defects in the fetus, such as Down syndrome or trisomy 18, is called into question. The triple test does NOT diagnose Down syndrome , Edwards syndrome or Patau syndrome, but only provides an estimate of the risk of developing a pregnancy with chromosomal abnormalities. It is only a starting point for recommendations for further investigation.
A negative result does not always mean that the baby will be completely normal, as not all types of birth defects are detected.