The triple screen or triple marker test is a probabilities test. It indicates the possibility of the fetus having an anomaly, but it does not provide a surefire diagnostic such as amniocentesis. If the test shows there could be a problem, it can be confirmed or ruled out by implementing other tests.  

What is the triple screen test?

It is a blood test that measures the presence of a substance called alpha-fetoprotein along with the mom’s blood levels of two hormones: estriol and gonadotropin. It measures three components; that are why it’s called triple screen (although nowadays there are many other tests that measure more than three components). 

If the levels of alpha-fetoprotein and estriol are low, and the level of gonadotropin is high, it is considered that the baby could have some chromosomal anomaly, such as Down’s syndrome.  

Other analyses of the mother’s blood

Besides the triple screen in the latest years, other kinds of analyses are also being carried out such as the quadruple marker. This measures one more hormone, called inhibin A, which determines more precisely the possibility of having a problem.

There is another test that is being used more and more and that measures the level of a hormone and a protein in the mother’s blood: PAPPA-A and B-HCG respectively.

Both the triple screen and this test are done between weeks 15 and 20 of pregnancy.

Nuchal translucency screening test

A test that is being widely used lately in combination with blood tests is the nuchal translucency screening test. This test helps determine whether the baby has Down’s syndrome. It is basically an ultrasound that checks the baby’s neck fold. Babies with Down’s syndrome usually have a thicker than normal neck fold. This test, along with blood-tests, is very reliable.   

Because this test involves interpreting the ultrasound images, it is important that the technician doing it is experienced. Nuchal translucency screening is done between weeks 11 and 13 of pregnancy.  

False positives

If the test results indicate there could be an abnormality, don’t fret. These tests only indicate the possibility that something is amiss, but they don’t confirm it (like an amniocentesis does).

There are several reasons for which there could be a false positive result, but the most common are:  

• There is more than one baby on the way, and therefore hormonal levels vary.

• The weeks of pregnancy hadn’t been properly calculated and the baby is in fact older or younger.  

• Cigarettes, insulin or obesity could also alter hormonal levels.  

Even though false positives happen sometimes, the great advantage of these tests is that they hold no risk of causing a miscarriage.  On the other hand, the fact that a false positive occurs does not imply that you need to have an amniocentesis. Some moms prefer to go for a level II ultrasound. 

In general, if there is a positive result, the tests are repeated in order to confirm the result, before going for more invasive tests to find out whether there is a problem.