Prenatal screening 2nd-trimester 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 had a family history of birth defects or birth disorders, women above 35 years of age, considering the weight of women, diabetes, ethnicity, etc.
Estriol: It is an estrogen that comes from the placenta and the fetus. If the estriol levels are low it may indicate Down’s syndrome. Down’s syndrome is the 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’s syndrome.
Hence this test helps in detecting if the baby is suffering from any genetic disorders like Down’s syndrome or Edward syndrome. Edward’s 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.
Inform your doctor if you are on any medications, have any allergies or underlying medical conditions before your Prenatal Screening 2nd Trimester. Your doctor will give specific instructions depending on your condition on how to prepare for Prenatal Screening 2nd Trimester.
There is no preparation required for this test.
Before interpreting the results one should keep in mind that this is not a diagnostic test but a screening test.
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. If the estriol levels are low it may be due to Down’s syndrome. If the 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. If the inhibin A levels are high it may indicate Down’s syndrome or Edward syndrome.
If you get abnormal test results it may indicate neural tube defects, Down’s syndrome, Edwards syndrome, multiple pregnancy (twins or triplets), the pregnancy which takes a long time than the timeline or pregnancy which takes less time than the timeline.
If you get abnormal test results, consult your doctor immediately. Your doctor may recommend other tests depending on your test results.