Prenatal genetic screening tests



genetic screening test
genetic screening test

During pregnancy, the parents to be have not only to look after the mother, but also they have to worry about and protect the baby growing inside the mother’s womb. When you go to visit your gynecologist for the first time you may be asked to take a lot of vitamin, iron and folic acid tablets. A gynec may also perform routine blood and urine tests and perform an ultrasound. Apart from that the gynec will also ask for prenatal genetic screening tests.

What are prenatal genetic screening tests and why should we get it done ?

Prenatal genetic screening tests are performed to see if there is any genetic defect in the growing fetus or not. The genetic defects occur in a fetus due to changes in the inherited genes or chromosomes. In most of the cases both the parents might be carrying the defective gene, which is non expressive in their body. This gene may become active in the fetus, due to some mutation. Hence, it is very necessary to get the prenatal genetic screening test done. Some of the disorders that can be diagnosed before hand with prenatal genetic screening tests are cystic fibrosis, sickle cell anemia, thalassemia, polycystic kidney disease, Hemophilia A, duchenne muscular dystrophy etc.

The prenatal genetic screening tests

Prenatal screening test is not a single test, but a bunch of test that are performed to study the fetus’s well being. These test include the following other tests

  • Ultrasound scan
  • Alpha feto protein test or Multiple marker test
  • Chorionic villus sampling
  • Amniocentesis

Ultrasound scan

In ultrasound high frequency sound waves are used to develop the image of internal organs or developing fetus on the screen of the machine. During pregnancy ultrasound is performed to verify the due date, to observe the development of the fetus. It also shows the number of fetus. Ultrasound helps in diagnosing ectopic pregnancy and fetal abnormalities. As the time of pregnancy progresses ultrasound is also used to measure the size of placenta, the growth of fetus and the position of the fetus. There are two main types of ultrasounds that are performed

  • Transvaginal ultrasound
  • Abdominal ultrasound
Transvaginal ultrasound

It is used in the early stages of pregnancy. In this an ultrasound transducer is inserted into the vagina and it rests on the back side of vagina. It gives a sharp clear image of the fetus.

Abdominal ultrasound

An abdominal ultrasound is the one in which jelly is applied over the abdomen and the screening is done. Most of the times the images taken are of 2D ultrasound.

If there is a need of more detailed scan than a 3D ultrasound imaging can be done. The 3D ultrasound needs a special machine and a specialist trained into it. The 3D image allows the radiologist to observe the height and the width of the developing fetus’s organs.

According to the latest technology. You can also have a 4D sonogram.  Through this you can see the live movements of the unborn baby in your uterus. This images can be captured in photos or on CD drive.

Alpha fetoprotein test

Alpha-fetoprotein or AFP is the protein that is produced by the liver of the fetus. This protein is present in the amniotic fluid surrounding the fetus. This protein crosses the placenta and enters into the mother’s blood system. The Alpha fetoprotein test is performed on the mother’s blood serum. The level of Alpha-fetoprotein in the mother’s serum tells the doctor a lot about the fetus’s health. The Alpha fetoprotein test is also known as maternal serum alpha-fetoprotein test.

The abnormal levels of AFP suggest the possibility of the following:

  • Chromosomal abnormalities
  • Defect in the abdominal wall of the fetus
  • Miscalculated due date
  • Down syndrome
  • Open neural tube defects like spina bifida

Chorionic villus sampling

Chorionic villus sampling is the procedure done for testing of certain chromosomal and genetic disorders. This procedure is performed when the mother has a genetic history of chromosomal or genetic disorders. In this process a small piece of the placenta is removed and sent for blood tests. This test is usually performed between 10 and 13 weeks of pregnancy. In this test a small catheter is inserted through a woman’s vagina into her cervix. The exact procedure is as follows

  • A catheter is inserted from a woman’s vagina into the cervix
  • Ultrasound is used to guide the catheter through the entire process
  • Tissue is removed with the help of syringe present on the other end of catheter
  • The sample is sent to the genetic laboratory for testing
  • The result is obtained at an interval of 10 to 15 days

Sometimes we may still not get 100% accurate results. In such cases, the test may be done for the second time. The women may experience some cramping after CVS.


This process involves the gathering of a certain amount of amniotic fluid. A long needle is inserted through mother’s abdomen. The entire process is as follows

  • Clean the abdomen with an antiseptic
  • The doctor may or may not give a local anesthetic to numb the skin
  • Guide the needle with the help of an ultrasound
  • Send the amniotic fluid to a genetic lab for testing
  • Woman may feel some cramping after this procedure

The lab results will arrive at an interval of 10 to 15 days. It will also measure the amount of alpha-fetoprotein present in the amniotic fluid. This helps to know about the defect called open neural tube defect.

These are a few tests that tells us about the genetic disorders that may be present in the developing fetus.


Himali Parikh
Himali Parikh
Himali is Parenting Blogger and founder of She had done M.S in Molecular biology from University of New Haven (US) and was working with various Pharma companies. She had started this motherhood and baby care blog for helping other mothers.

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