The triple screening, also called triple test is a screening test or scan that is performed in the pregnant woman to detect foetal genetic disorders.
It is a non-invasive test, because no one enters the uterus, which is made from a blood sample from the mother. It is a routine intervention consisting of a simple blood test without risk to the mother or the foetus.
It is not conclusively proved that it’s not a diagnosis but an index measuring risk that the foetus has certain chromosomal abnormalities such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) and neural tube defects.
Triple screening in the first trimester of pregnancy
It consists of a chromosomal risk assessment obtained by combining three biochemical markers in the blood of the mother (hence the name triple screening): PAPP-A (alpha-fetoprotein, a protein produced by the foetus), beta- HCG free (human chorionic gonadotropin), the pregnancy hormone produced by the placenta and free estriol (oestrogen produced by the foetus and placenta).
Some laboratories also measure a fourth parameter, inhibin A, which is termed as quad screen, but not too extended.
These values intersect with biochemical data from the nuchal translucency measurement of the foetus by ultrasound and are weighted by demographics (maternal age, race, weight, smoker, or have diabetes) yielding a control algorithm that measures the possibilities that the foetus has an abnormality.
When the risk is greater than 1 in 270 (read 1 / 270 or 1:270), i.e. when the value is less than 270, which equals to or is below the cut, is recommended as a more accurate test amniocentesis or chorionic villus sampling to rule out or confirm the risk. In the next post will talk more in detail about the values of the triple screening.
In women younger than 35 years, it’s detected between 75 and 85 percent of neural tube abnormalities and 60 percent of cases of Down syndrome. In women over 35 years detected 75 percent of neural tube defects and Down syndrome cases.
Besides being used to detect chromosomal alterations, triple screening serves to identify a multiple pregnancy and pregnancies that are more or less advanced than you think.