Second Trimester Screen

A second-trimester screening test is performed in pregnant women between 15 to 20 weeks of pregnancy. This test is used to detect any genetic disorders in the fetus. It measures the levels of unconjugated estriol, human chorionic gonadotropin (HCG), alpha-fetoprotein (AFP), and inhibin A. These three are the important substances in the placenta. This is mostly recommended in pregnant women who have a family history of birth defects or birth disorders, women above 35 years of age, abnormal body habitus, diabetes, and ethnicity, etc.

Test Parameters:

• Unconjugated estriol
• Human chorionic gonadotropin (HCG)
• Alpha-fetoprotein (AFP)
• Inhibin A

What is the importance of this test?

This test helps in detecting if the baby is suffering from any genetic disorders like Down syndrome or Edward syndrome. Edward syndrome is a condition which leads to severe developmental delays due to chromosome 18 abnormality. This is a very beneficial method to detect any genetic defects in the baby before their birth. This test provides a probable ratio of the unborn baby having a chromosomal defect. If the ratio is high then further tests like amniocentesis should be carried out.

Estriol: It is an estrogen that comes from the placenta and the fetus. If the estriol levels are low, it may indicate Down syndrome. Down syndrome is a delay of growth, development, and intelligence due to chromosome 21 disorder. This will be more prominent if the alpha-fetoprotein is low and human chorionic gonadotropin levels are high.

Human chorionic gonadotropin (HCG): This is a hormone produced by the placenta. If human chorionic gonadotropin levels are decreased, it may indicate problems with pregnancy, like miscarriage or ectopic pregnancy (where the fetus grows outside the uterus, mostly in the fallopian tube). If the human chorionic gonadotropin levels are increased, it may indicate a molar pregnancy or a pregnancy with two or more children called as multiple pregnancy.

Alpha-fetoprotein (AFP): This is a protein produced by the fetus. If this alpha-fetoprotein level is raised, it may be due to potential defects like neural tube defects or failure of the fetus’s abdomen to close.

Inhibin-A: This is a hormone released from the placenta which may indicate the possibility of the fetus having Down syndrome.

This test helps in detecting if the baby is suffering from any genetic disorders like Down’s syndrome or Edward syndrome. Edward syndrome is a condition which leads to severe developmental delays due to chromosome 18 abnormality. This is a very beneficial method to detect any genetic defects in babies before their birth. This test provides a probable ratio of the unborn baby having a chromosomal defect. If the ratio is high then further tests like amniocentesis should be carried out.

There is no preparation required for this test.