After a woman gets pregnant, prenatal tests are performed to assess the woman's and her unborn child's health during the length of the pregnancy. These tests can identify conditions that, if left untreated, might put a baby at risk for issues, including premature delivery, and they can also assist medical professionals in identifying chromosomal abnormalities or birth defects. 

However, certain tests used during pregnancy are screening tests that can merely indicate the potential for a health problem, and in those cases, additional prenatal tests and diagnostic techniques are used to precisely determine whether a fetus has a certain issue. In India, every year almost 500,000 babies are born with genetic disorders, and to prevent that scenario, performing a prenatal test should be a top priority.  

What is a Prenatal Screening Test?

Prenatal screening tests refer to a broad range of tests that your doctor may prescribe during pregnancy. To ascertain if a child is likely to have particular medical disorders or chromosomal abnormalities, such as Down’s syndrome, several prenatal screening procedures are performed. The majority of these screening tests are done in the first and second trimesters, so your doctor will inform you about these tests during your first visit. The majority of OBs advise a prenatal screening test, and they are typically optional, however, prenatal screening tests are standard practices since they check for health conditions that might impact you, your pregnancy, or your unborn child. 

Prenatal Diagnostic Tests  

During your first visit to your OB, they will give you these diagnostic tests to check for typical issues that often occur during pregnancy. These are usually non-invasive tests, and you shouldn’t have any health difficulties during these. 

1. Blood Tests

A sequential integrated screening test and a serum-integrated screening are among the main prenatal screening and diagnostic tests that your doctor may request during the first trimester. They are used to determine the concentrations of specific chemicals in your blood, such as the hormone human chorionic gonadotropin and pregnancy-associated plasma protein A. Your blood may also be checked for syphilis, hepatitis B, and HIV at your initial prenatal checkup, as well as to determine if you have had the rubella vaccine or have anemia. Your blood type and Rh factor, which establishes your compatibility with your developing child, will also be examined by a blood test.  

2. Ultrasound

An ultrasound is another common prenatal testing during pregnancy. It creates a picture of the fetus within the uterus using sound waves, measures your baby's growth and position, and also looks for any possible anomalies. Between weeks eleven and fourteen of pregnancy, a unique ultrasound known as nuchal translucency ultrasound is conducted, and this ultrasound examines the fluid buildup at the nape of your infant's neck. There is an increased chance of Down’s syndrome when there is more fluid than usual, however, it's not definitive. 

3. Glucose Screening

Gestational diabetes is a disorder that can occur during pregnancy. Regardless of whether you are deemed high risk or not, this glucose screening test is rather typical for everyone, and even if you have never had diabetes before, you might still have gestational diabetes. Mothers with gestational diabetes typically give birth to bigger infants, so having the condition might raise your risk of needing a cesarean delivery and in the days after delivery, your infant can potentially have low blood sugar. You should obtain the test again after the pregnancy if you do test positive for gestational diabetes since you have an increased chance of getting the disease in the next ten years.

4. Chorionic villus sampling

A little sample of placental tissue is taken as part of this screening procedure known as chorionic villus sampling (CVS), and only after a previous noninvasive screen yielded abnormal findings, your doctor could recommend this test. It is often carried out between weeks ten and twelve and is used to screen for genetic disorders, including cystic fibrosis and chromosomal abnormalities. Two varieties of CVS tests - the transabdominal test, which is performed via the abdomen, and the transcervical test, which is performed through the cervix.  

5. Quad Marker Screening Test

Your doctor can use a quad marker screening test to determine if you have a higher chance of giving birth to a child who has Down’s syndrome, neural tube defects, or abnormalities of the abdominal wall. If you begin prenatal care too late to undergo either the sequential integrated screening or the serum integrated screening, you will usually be offered a quad marker screening test. 

Types of Prenatal Genetic Testing and What to Expect 

With the advancement of medical testing procedures, performing genetic testing when pregnant has become a common practice! These screening tests are not used to diagnose genetic disorders and they only indicate a greater chance of developing a genetic condition. The findings of genetic screening tests will be explained to you by your healthcare professional, and they will also instruct you on what to do next. 

There are many different types of prenatal genetic testing so let's take a look.  

1. Carrier Screening

You and your partner may be offered a blood test called carrier screening by prenatal care professionals, and small genetic alterations that raise the fetus's chance of developing severe illnesses can be found using this kind of testing. Sickle cell disease, spinal muscular atrophy, and cystic fibrosis are a few examples of the issues that can be found through this test! Your spouse should be screened as well if your blood test indicates that you are a carrier for a genetic risk because the fetus may have a more severe version of the condition if both parents carry the same genetic risk.  

2. Screening for an Abnormal Chromosome Number

One-half of each pair of chromosomes is inherited from each parent, however, in some cases, during fertilization sections of the chromosomal pair become absent. Turner's syndrome (a missing X chromosome) and Down’s syndrome (an extra chromosome) are two diseases that can be caused because of this anomaly. There are multiple ways to perform this test. 

Cell-free fetal DNA screening	In tiny fragments of fetal DNA detected in your blood, healthcare professionals search for certain types of aberrant chromosomal numbers. However, due to the extremely low levels of fetal DNA, the test cannot be performed until ten weeks of pregnancy.
Serum screening	It doesn't examine fetal DNA directly, rather these tests assess different blood protein levels to identify the likelihood of aberrant chromosomal numbers. Sequential screening, quad screening, and first trimester serum screening are a few examples of this kind of examination.

3. Screening for physical abnormalities

Your baby's physical structure may occasionally alter as a result of additional or missing chromosomes. Blood tests and ultrasounds can be used to examine the fetus's risk for physical abnormalities, and additional tests establish whether or not they are caused by genetic abnormalities. The nuchal translucency test measures the thickness of the fetus's neck using ultrasonography, and doctors could learn about the likelihood of physical problems such as improper fetal heart construction and aberrant chromosome number from this test. 

Final Remarks

Various types of prenatal screening tests are now standard practice as they can lower the chance of health problems in the mother and the unborn baby! These tests offer doctors valuable information about how the pregnancy is progressing and whether the fetus has defects. Whenever your doctor recommends certain screening tests, it is best that you take them even though they are optional. 

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