Reasons behind Sequential Screening

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Sequential screening is a group of tests involving the use of blood and ultrasound to examine genetic abnormalities and defects of the neural tube of the fetus in a pregnant woman.

During pregnancy, the proteins and hormones produced by the fetus move into the blood of the mother while the mother on her own also produces additional hormones and proteins to support the growth of the baby. This condition brings about abnormalities in the growth of the baby.

The screening is effective in detecting Down syndrome and trisomy 18 which are prominent chromosomal abnormalities. Processes involve in the sequential screening test

As said earlier, the test involves the use of blood and ultrasound scan. The one involving blood usually takes place twice; the first is from 11th to 13th week of pregnancy while the second is usually done in the 15th and 18th week of pregnancy. This test being done n the first and second trimesters offer precision in the sequential screening test.

On the other hand, the ultrasound process is done in the 11th and 13th week of pregnancy with focus on the fluid-filled space in the back of the neck of the baby to check for nuchal translucency.

Uses

Sequential screening test (SST) is used to measure pregnancy related plasma protein (PAPP-A). A low level PAPP-A indicates a higher risk for developing neural tube defects.

Similarly, SST also measures the amount of alpha-fetoprotein (AFP) in the liver of the baby which passes over into the mother’s blood. Too-high and too-low levels of AFP are both linked to some birth defects.

SST also measures estriol (uE3) which is the highest amount of circulating hormone in a woman’s blood during pregnancy. Low levels of this hormone are linked to greater risk for Down syndrome and trisomy 18.

SST in addition to the above also indicates the amount of human chorionic gonadotropin (hCG) in various stages of the pregnancy. Low levels of hCG causes trisomy 18 while high levels of hCG resulted in Down syndrome.

Level of accuracy and reliability of the SST
While it is not possible to detect all possible genetic disorders in all pregnant women, the sequential screening test accuracy lie mainly on the screening results as well as the skill of the doctor handling the ultrasound. however, the sequential screening test is highly reliable in detecting potential genetic abnormalities.

Important tips
A pregnant woman should discuss with the doctor on the associated benefits
of a sequential screening. In a family with Down syndrome history, it is important to undergo the test. A patient whose result is positive needs to consult with a counselor to enjoy further explanation on the possibility of having a baby with abnormality.