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Prenatal Genetic Testing During Pregnancy: Types of Genetic Screening Tests

Genetic Testing During Pregnancy

Every pregnant woman should undergo several diagnostic and screening tests to acquire information about the health of the fetus. These tests are crucial as they can detect conditions like spina bifida and Down Syndrome. While these tests are mostly optional, they will let you know what to expect once the baby arrives. So, having some idea about genetic testing during pregnancy will make it easy for you to decide if you should get such tests done.

Prenatal Genetic Screening: An Overview 

Prenatal Genetic Testing During Pregnancy

Genetic testing means studying an individual’s DNA to identify susceptibility to specific abnormalities or diseases or genetic differences. There are different kinds of tests like carrier screening tests, integrated screening, alpha-fetoprotein test, and so on. These tests can be done during and before pregnancy.

So, what diseases can be detected through genetic testing during pregnancy? Should you undergo these tests during your first or second trimester? Let’s find out everything about first trimester screening tests and second trimester screening tests.

Prenatal Genetic Tests: Major Types

An abnormal result during a screening test does not mean the baby has a condition. It indicates that the chances of genetic disorder can be higher in the fetus. So, let your doctor interpret the outcome of the prenatal screening test before taking the next steps. In some cases, the doctor may suggest diagnostic testing. These are some instances of prenatal genetic screening:

1. Carrier screening

Career screening is a kind of blood test and your gynecologist may ask you to do it. This testing can spot minor alterations in the genes that double the risk that your baby could end up inheriting critical medical conditions from you. These are termed single-gene conditions. Sickle cell disease, spinal muscular atrophy, and cystic fibrosis are some ailments that genetic carrier testing can detect.

If the blood test proves you are a potential carrier for some kind of genetic risk, both you and your partner should undergo screening. When both the mother and the father are diagnosed as carriers of the same risk, a more serious form of the same disease can affect the fetus. You won’t have to complete genetic carrier screening test more than once in a lifetime.

2. Screening to detect abnormal chromosome number

A baby needs to inherit chromosomes in pairs – one half of it from each one of the parents. However, at times nature makes errors during fertilization, leading to extra, or missing parts of the pair. Down syndrome and Turner’s syndrome are two examples. The results will differ during each pregnancy and the two types of tests are:

  • Serum screening

Serum screening test is also done on a mother’s blood sample. Instead of looking directly at the DNA of the fetus, this test analyzes the protein levels in the mother’s blood to figure out the chances of irregular chromosome numbers. Instances of this kind of test include quad screening, first trimester genetic tests, and sequential screening.

Note that there are specific times during a person’s pregnancy when these tests should occur. Hence, check with your doctor about which test you should do. Until the 11th week of pregnancy, you aren’t supposed to undergo any of the above-mentioned tests.

  • Cell-free fetal DNA screening

The other name for it is non-invasive prenatal testing, abbreviated as NIPT. Doctors look for some forms of irregular chromosome numbers in the fetus after collecting your blood samples. As fetal DNA is not present in large amounts, path labs cannot perform the DNA testing until 10 weeks of a pregnant woman’s gestation.

3. Screening to identify physical abnormalities

Under certain circumstances, extra or missing chromosomes cause alterations in a fetus’s physical structure. For instance, the baby can have a physical abnormality even when the chromosomes are perfect. So, during pregnancy, blood tests and ultrasound are necessary to determine if the fetus is developing physical abnormalities. After that, the physician attempts to understand if the abnormalities are because of genetic reasons by following these methods:

  • Nuchal translucency

Nuchal translucency is the process of using ultrasound for measuring the thickness of the fetus’s back portion of the neck. If the nuchal translucency is thick, it gives a hint that the chromosome number can be abnormal in the fetus and the heart may not be completely developed. The best time to perform the ultrasound is between 11 and 14 weeks of gestation.

  • Quad screen

Quad screen is essential to measure the amount of four substances present in your blood. It can rule out chances of the fetus being born with neural tube defects or chromosomal abnormality. This test may also be known as a multiple marker screen. Doctors perform it between 15 and 22 weeks of gestation.

  • AFP screening

During AFP of maternal serum screen, a healthcare professional will draw some blood from your system to know the level of AFP present in your blood. If the levels of AFP are high, the baby may be born with birth defects in the spine, face, or abdomen. The right time for this test is between 15 and 22 weeks gestation.

  • Fetal anatomy scan

Ultrasound is used during a fetal anatomy scan to evaluate the physical structure of the fetus. This ultrasound should be done between 18 and 20 weeks of gestation, and it can evaluate various body parts like face, arms, legs, abdomen, kidneys, heart, brain, and skeleton.

Prenatal Diagnostic Tests: Types

Diagnostic prenatal tests collect cell samples from the placenta or amniotic fluid and then test them for diverse disorders. These tests are crucial to confirm if the fetus is developing a genetic condition. Doctors perform diagnostic testing only when the results of screening tests are alarming or indicative of genetic abnormalities.

Two of the most popular diagnostic tests are CVS (chorionic villus sampling) or amniocentesis.

CVS 

Your doctor will insert a fine needle into the uterus and remove a sample of cells from the placenta. The needle can be placed through your vagina or abdomen. CVS generally occurs somewhere between the 11 and 13 weeks of pregnancy. The provider will send the sample to a testing lab, and you should get the result within 72 hours.

Amniocentesis 

A healthcare provider will insert a needle through the mother’s skin into the uterus and to collect amniotic fluid sample from the amniotic sac. Amniocentesis takes place 16-20 weeks after becoming pregnant.

Who Should opt for Genetic Testing?

Getting prenatal testing is a personal choice and if you are confused, you may consult a genetic counselor for reliable genetic counseling. As it is not mandatory, most couples skip it. However, some parents want to know if their baby will be completely healthy. As the results give significant information about your baby’s health, most healthcare providers recommend it as part of pregnancy care.

Some reasons why families prefer genetic testing during pregnancy are:

  • Personal or family history of genetic disorders
  • History of stillbirth or miscarriage
  • Pregnancy after the age of 35

Wrapping Up

The bottom line is to remember that genetic testing during pregnancy helps healthcare providers and families make important decisions about the fetus and the pregnancy. So, if you are planning a baby or you have conceived, testing will offer you a closer look into the health of your baby.

Frequently Asked Questions

1. What is genetic testing during pregnancy?

Genetic testing is an umbrella term that encompasses various tests that can benefit parents-to-be. Through these tests you can find out if the baby in your womb has some genetic condition caused by alterations in a person’s chromosomes or genes.

2. How is genetic testing done during pregnancy?

There are several methods to detect birth defects genetic tests. The doctor can collect blood samples of the parent or perform an ultrasound to figure out the type of abnormality in the fetus.

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