Prenatal testing : Be safe do not be sorry!

  • By Team TDO

Types :
Prenatal testing includes both screening and diagnostic tests:

Screening tests:
Prenatal screening tests indicate that the baby most likely to have been affected by certain condition. However, these tests do not confirm the diagnosis. Certain blood tests and ultrasonography are routinely done as a part of the screening procedure. Specific screening tests to detect genetic abnormalities in developing baby are also done sometimes in high-risk pregnancies. These screening tests do not pose any risk either to the mother or to the baby. Fetal ultrasound often plays an important role in prenatal care. Early in pregnancy, an ultrasound can be used to confirm and date a pregnancy. Later on it’s used for prenatal screening.

Diagnostic tests:
If a screening test indicates a possible problem then a definitive diagnostic test is undertaken. Additional information like age of the mother, family or medical history of the parents also provides valuable information to the doctor to decide to undertake the diagnostic tests.

First trimester screening:
The first three months of pregnancy is called the first trimester. First trimester screening combines results of two tests - ultrasonography and blood test - to indicate any possible birth defect in the developing baby. The ultrasonography measures the thickness of an area behind the back of the baby’s neck called nuchal translucency test. Increased thickness indicates increased risk of birth defect. The blood test measures the level of beta-human chorionic gonadotropin (beta-hCG) in blood. Increased level of beta-hCG may be associated with birth defects.

Triple screening:
This is usually done between 15 to 20 weeks of pregnancy. In this test, blood level of three substances – alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and estriol are measured in pregnant mother’s blood. Abnormal blood level of these substances indicates possible birth defects that are confirmed later by diagnostic tests.

Diagnostic tests

If results of above mentioned tests indicate any risk of birth defects, further diagnostic genetic tests are conducted. This diagnostic testing is called karyotyping. Karyotype is used to examine the size, shape, and the number of chromosomes. These tests are more accurate and reliable than screening tests. Karyotype can be done by following ways:

  1. Amniocentesis – Small sample of fluid that surrounds and protects baby during pregnancy is removed from uterus.
  2. Chorionic villus sampling (CVS) - A small part of developing placenta is removed for testing.

These samples are examined and tested for extra, missing and abnormal positions of chromosomes that indicate birth defects in a developing baby.


Chromosomal abnormalities are incurable. In case of confirmation of a chromosomal abnormality, the pregnant mother needs to decide about future course of pregnancy - continuation or termination. The healthcare providers and counselors can offer help in these matters.