Introduction
Prenatal genetic testing informs the parents if the fetus has some genetic disorders. Prenatal genetic testing helps families and doctors make apt decisions about the pregnancy or the fetus. The healthcare providers may not compulsorily ask the parents-to-be to take prenatal genetic testing.
What Is Meant by Prenatal Genetic Testing?
The genetic disorders of the fetus can be known with the help of prenatal genetic testing. Changes in chromosomes or genes cause genetic diseases. Changes in genes called mutations cause inherited disorders. The doctor may give the parents the option for prenatal genetic testing but will not ask to do it compulsorily, unlike other blood tests or glucose screening tests.
Why Is Prenatal Genetic Testing Important in Perinatal Medicine?
Prenatal genetic testing plays an important role in perinatal medicine. Prenatal genetic tests are mainly of two types: Prenatal diagnostic tests and screening tests. Each test plays a vital role in perinatal medicine.
Prenatal Diagnostic Test:
The genetic condition of the fetus can be confirmed using prenatal diagnostic tests. It includes the following types:
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Ultrasound Scanning: Ultrasound scanning is a noninvasive examination that uses sound waves. A small transducer device will be used to get a picture or image based on the differences between body tissue density. It will be advised to take ultrasound scans during pregnancy on a fixed interval to know the gestational age, number of babies, and growth level of the fetus and to assess the placental condition.
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Fetal Echocardiogram: The functioning and structure of the fetal heart can be assessed with the help of a fetal echocardiogram. It is done similarly to fetal ultrasound scanning. But more precise images of the fetus’s heart structure and functioning will be obtained using the procedure. The healthcare provider will be able to understand the time for delivery by getting a picture of the heart functioning. In addition, any defects in the fetus can be known prior, and the doctors can plan for therapies to manage the conditions.
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Fetal Magnetic Resonance Imaging (MRI): In the case of fetal MRI scanning, a magnetic field will be used to assess the fetus's condition. Fetal magnetic resonance imaging is considered a supplemental diagnostic test to ultrasound scanning.
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Cordocentesis: Cordocentesis is the fetal blood sampling procedure. In this procedure, a blood sample will be obtained from the umbilical cord of the fetus. It helps detect mutations, blood disorders, or infections in the fetus. It is an invasive procedure and will be done only when the noninvasive techniques fail. Fetal or uterine infection, blood loss in the mother or the fetus, umbilical hematoma, and other complications may arise due to the procedure.
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Amniocentesis: The medical procedure by which the amniotic fluid is drawn from the amniotic cavity is called amniocentesis. It is an invasive fetal diagnostic procedure. Amniotic fluid will be taken by the doctor with the help of a small syringe inserted into the uterus. Genetic and chromosomal conditions like Down’s syndrome, cystic fibrosis, and others can be diagnosed with this procedure.
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Chorionic Villus Biopsy: Chorionic villus biopsy or sampling is done by inserting a needle into the abdomen or by ultrasound method. A sample of tissues from the placenta will be taken for the procedure.
Prenatal Screening Tests:
Prenatal screening tests can determine the chances of chromosomal or genetic disorders. After the screening test, the doctor may ask to take a diagnostic test. The following are some types of prenatal screening tests:
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Carrier Screening Test: Carrier screening tests can identify small genetic changes. It is mainly done if the fetus has a chance to inherit certain medical conditions from the parents. The partners will be asked to take a carrier screening test to check for the probability of passing on specific medical or genetic disorders to the fetus.
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Prenatal Cell-Free DNA Screening: Prenatal cell-free DNA screening or cfDNA is a blood test done for prenatal screening in pregnant women. The cfDNA tests the fetus’s DNA (deoxyribonucleic acid) circulating in the mother's bloodstream. It is often used to find out if the fetus has disorders like Down’s syndrome (trisomy 21), Pattau syndrome (trisomy 13), and Edwards syndrome (trisomy 18). It may also be used to determine the gender of the unborn baby.
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Prenatal Serum Screening: Prenatal serum screening analyzes the protein levels in the blood. These tests will be recommended at certain intervals during pregnancy and can only be done after eleven weeks of pregnancy.
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AFP (Alpha-Fetoprotein) Screening: AFP screening test checks for the level of alpha-fetoprotein or AFP in the mother’s blood. AFP screening test is done between fifteen to twenty weeks of pregnancy. High levels of AFP in the blood may indicate that the fetus has neural tube defects or Down's syndrome.
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Nuchal Translucency (NT) Test: Nuchal translucency or NT test is an ultrasound scan the doctor may sometimes ask to perform on the pregnant woman in the pregnancy’s first trimester. It measures the quantity of fluid behind the baby’s neck. An average amount of fluid indicates a lower chance of having a genetic condition in the fetus. The chances of congenital or genetic disorders increase if the fluid amount is more.
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Quad Marker Screening: Quad marker screening or quad screen can be done between 15 to 22 weeks of pregnancy or the second trimester. It measures the amount of four substances in the mother’s blood, hence the name quad screen: inhibin-A, alpha-fetoprotein or FPA, human chorionic gonadotropin or HCG, and a type of estrogen called estriol. It mainly detects the chances of developing Down's syndrome, neural tube defects, or Edwards syndrome.
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20-Week Ultrasound: 20-week ultrasound or fetal anatomy scanning is performed between 18 to 22 weeks of pregnancy. It is also called anomaly scanning. Congenital disorders, anatomic defects, and physical development of the fetus can be detected with the help of this scanning.
Conclusion
Prenatal genetic testing plays an important role in perinatal medicine. Diagnostic and screening tests help detect genetic or chromosomal defects in the unborn baby or the fetus. Knowing the presence of such defects helps the doctor and the parents stay prepared for the baby's post-natal treatments.
