Prenatal Genetic Screening can be defined as information on the fetus and their genetic disorders. The change in the genes or chromosomes causes a genetic disorder. There are two types of prenatal genetic tests, prenatal screening tests predicting the chances of the fetus having aneuploidy and other disorders and prenatal diagnostic tests where the fetus has particular disorders. The tests are conducted on the fetus or the placenta taken from the amniocentesis or chorionic villus sampling. These two tests are must for all pregnant women. Most of the prenatal genetic screening is noninvasive and are performed during the first and second trimester of pregnancy. Some even continue through the third trimester as well.
Prenatal Genetic Screening
Prenatal Screening test routines
- Glucose tolerance test for those with gestation diabetes
- High risk of being born with certain conditions, for instance, pregnant women living in tuberculosis prone region have to undergo tuberculin skin test
First Trimester Screening Test
The ultrasound is used to create the image of the fetus in the uterus. It determines the size and position of the baby and finds potential abnormalities in the growth of organs and bones. Nuchal translucency ultrasound is performed between 11 and 14 weeks of pregnancy to check for fluid accumulation in the baby’s neck. When there is more fluid, it means a higher risk of Down Syndrome.
There are two types of blood tests, sequential integrated screening test and serum integrated screening tests. It measures the substance levels in the blood like plasma protein A and human Chorionic gonadotropin hormone levels. Rh compatibility test is also conducted to determine the compatibility.
Types of Prenatal Genetic Screening Test
A screening test predicts the risk of having a baby with particular disorders. These include prenatal genetic and carrier screening tests. The former screens for aneuploidy in the fetus, neural tube defects in the brain and the spine and defects in the abdomen, facial features and the heart. The first-trimester screening is done during the 10 and 13 weeks of pregnancy. It measures certain substances in the blood and ultrasound. The Genetic screening is done during the second trimester. Screening tests can help parents know if the fetus has a high or low risk of chromosomal abnormality. It helps to understand the genetic makeup of the fetus.
Accuracy of prenatal genetic screening
Any test has two outcomes, false positive and false negative. The test results when there is a problem when it does not exist can be called false positive result. The test result showing there is no problem when it exist can be called false negative result. The meaning of the value is determined by your healthcare professional.
While considering prenatal genetic testing, it is important to go by your values and beliefs. Remember a positive screening test will be able to place the risk of the baby having Down syndrome or other aneuploidy. For precise results, go for the diagnostic test. It helps the parents to decide whether to terminate the pregnancy or make arrangement for medical care for the child.