Is It Right To Do Prenatal Testing? Types And Diagnosis

Specific screening tests are often needed since not all conditions are confirmed by regular ultrasound and blood tests.

Written by Rebecca Malachi • 

Regular tests for each trimester are essential for prenatal care. You are advised to take these tests to track the progress of your pregnancy throughout the gestational period. Most of these tests are routinely performed. They are quick, painless, and beneficial to both the mother and baby. In addition, your obstetrician-gynecologist or genetic counselor may recommend some special tests to look for developmental anomalies or other complications. This post takes you through the various tests you will usually undergo during the three trimesters or nine months of pregnancy.

What Is Prenatal Testing?

Prenatal testing refers to the series of medical assessments you have over the course of pregnancy. They include blood tests, invasive and non-invasive genetic tests, ultrasounds, vaginal swabs, and electronic fetal monitoring that help your doctor understand yours and your baby’s health (1).

  • Some tests are routine and are usually performed in every pregnancy. They analyze the baby’s progression and check if you are in good health for holding the baby until delivery. The tests also help your doctor understand the need for any special treatments.
  • Some other tests are optional and are done if you opt for it and you are at risk of some complication. These optional tests help determine if your baby has any genetic abnormality or congenital disabilities.
  • If certain health conditions run in your family, you should talk to your genetic counselor. The specialist can help you know about the possible birth defects or conditions which can have an impact on you and your baby’s health.

Next, let’s see the regular and the specific tests that you may undergo during pregnancy.

What Are The Regular Prenatal Tests Performed During Pregnancy?

The following are the prenatal tests you have to take frequently during your pregnancy:

  • Blood pressure test: This is done to check if you have preeclampsia, a condition of high blood pressure and signs of organ damage mostly to the liver or kidneys.
  • Urine test: This is done to check for kidney and bladder infections, and conditions such as preeclampsia. High level of protein in urine could be a sign of preeclampsia.
  • Blood tests: They are done to find the blood type, Rh factor, thyroid function, and anemia. They also reveal infections such as hepatitis B, hepatitis C, HIV, and syphilis.

Additionally, weight is also determined during every prenatal checkup to understand if your weight gain is ideal.

What Are The Specific Types Of Prenatal Testing?

Prenatal tests are categorized into diagnostic and screening tests (2).

  • Screening tests: These tests identify your chances of having a baby with chromosomal abnormalities. They do not give definitive results but come with set parameters for results. If results are above or below a set level or measure, they are deemed positive and warrant further testing. There are no risks involved in doing these tests.
  • Diagnostic tests: These tests give definitive results if your baby has a genetic condition or congenital disability. The results are 99% accurate and usually follow screening tests. Diagnostic tests may pose some risks for you and your baby.

Keep reading for a detailed understanding of the tests done in each trimester of your pregnancy.

First-Trimester Pregnancy Tests

The list of tests in your first trimester, which is from week zero to week 13 (months 1, 2 and 3) is as follows.

TestWhat it isHow it is doneThe risks involved
Blood testsThe initial blood screening test checks for:
  • Blood type
  • Rh factor
  • hCG levels
  • Sexually transmitted infection (hepatitis B, HIV, and syphilis)
  • Immunity to diseases such as German measles and chicken pox
  • Vitamin D deficiency
  • Blood sugar levels
  • Genetic risks for sickle cell anemia, spinal muscular dystrophy (SMA), cystic fibrosis, thalassemia, hemoglobinopathy, and other possible diseases
A blood sample is collected using a needle and syringe and submitted to the lab for testingNo risks involved other than the discomfort of pricking and bruising (3)
Urine testsA quick urine test checks for the following:
  • High levels of blood sugar that indicates gestational diabetes
  • High protein levels that indicate preeclampsia
  • Levels of red or white blood cells and bacteria indicating urinary tract infections (UTI) (1)
You will provide a sample, and the technician uses a dipstick or puts some drops into the testing strips.No risks involved
Chorionic villus sampling (CVS)It is done between the 10th and 13th weeks to detect birth defects such as:
  • Genetic disorders such as cystic fibrosis
  • Chromosomal disorders, such as Down syndrome

It is usually suggested for those who are at a greater risk of genetic disorders (4).

A small sample of placental cells is withdrawn for testing.Some risks involved but generally safe and reliable
Non-Invasive Prenatal Testing (NIPT)It is performed after ten weeks of pregnancy and checks for chromosomal disorders including:
  • Down syndrome
  • Edwards syndrome
  • Patau syndrome

It also detects Rh blood type and the gender of the baby.

A blood sample is used to look at cell-free DNA for signs of abnormalities (5)Very low risks are involved
UltrasoundThe first ultrasound is done between 6 and 9 weeks to:
  • Check the estimated due date
  • Detect the fetal heartbeat
  • Rule out ectopic or tubal pregnancies
  • Detect the number of fetuses
It is done using a transducer or wand over the abdomen that emits sound waves, which bounce off to give a picture on the screen.Very low risks are involved (6)
Nuchal translucency screeningIt is performed between 11 and 13 weeks of pregnancy to determine the risk of Down syndromeIt uses a unique ultrasound to examine the thickness of the fetal neck to calculate the probability of a chromosomal defect (7).No risk involved

Apart from these, there can be additional screening or diagnostic tests depending upon the condition of the individual.

Second-Trimester Pregnancy Tests

These prenatal tests are commonly done in your second trimester (months 4, 5 and 6 of pregnancy):

TestWhat it isHow it is doneThe risks involved
AmniocentesisIt is performed between weeks 15 and 20 (sometimes much earlier) to check for:
  • Chromosomal conditions such as Down syndrome, Tay-Sachs disease, Sickle cell anemia
  • Neural tube defects such as spina bifida
A fine needle is inserted into the amniotic sac to draw the fluid containing fetal cells (8).Limited risks are involved with trained professionals
Cordocentesis/ Fetal blood sampling/ Percutaneous umbilical cord sampling

It is performed as early as 17th week and checks for:
  • Anemia and blood oxygen levels
  • Maternal Rh antibodies
A fetal blood sample is withdrawn from the umbilical cord or fetusFetal risks and infections can develop (9)
Quad screenThis is performed in between 15 and 18 weeks to check for chromosomal disorders and neural tube defects.

It measures four substances that pass into the mother’s bloodstream from the fetus: alpha-fetoprotein, hCG, unconjugated estriol and Inhibin-A (10).

Uses blood sample for testingCompletely safe
Level 2 ultrasoundIt is done anytime between 18 and 20 weeks to see how the fetus is developing (11).It uses a transducer that sends sound waves to view the ultrasound images on the screen.No risks are involved
3D and 4D ultrasoundThey are usually done when the pregnancy seems to be complicated. They examine fetal abnormalities such as neural tube defects and cleft lip palate or anything specific.Multiple two-dimensional images are captured at different angles using the hand-held ultrasound device (12).
Glucose screeningThis is performed in between the 26th and 28th weeks of pregnancy to determine your risk of gestational diabetes.

Based on the results, you may need a glucose tolerance test (1).

You will be asked to consume a sweet drink followed by a blood test for glucose levels.No risks involved
Glucose tolerance testIt is done in between 26 and 28 weeks to detect gestational diabetes (1).You do not have to fast before the test. But need to stop eating two hours before the test and avoid high-carb food. 

A blood test followed by consumption of sugary drink helps detect the condition of glucose intolerance.

While you will have a good idea of how your baby is doing by this time, your provider will do a few more tests to make sure the baby arrives healthy and in the best condition.

Tests During The Third Trimester Of Pregnancy

These prenatal tests are recommended in your third trimester (months 7, 8 and 9 of pregnancy):

TestWhat is itHow it is doneAre there any risks
Group B strep testIt is usually done between 35 and 37 weeks of pregnancy to screen for group B streptococcus bacteria (13).A swab is inserted into the vagina and another into the rectum, after which they are sent to a lab for testing and detecting any bacterial strains on the cells.No risks are involved
Nonstress testIt is performed anytime after the 28th week in the case of high-risk pregnancies, or if you are past your due date. It monitors the baby’s health and can show if the baby is in distress.A stretchable belt monitor is placed around the belly to track the fetal movements (14).
Biophysical profileIt is performed after 32 weeks of pregnancy when tests such as the nonstress test need a follow-up. It determines the risk of some possible complications and also decides if it is the time for delivery.An ultrasound wand is used along with an elastic band with two sensors around the abdomen to detect the fetal heartbeat, body movement, breathing, amniotic fluid levels and muscle tone (15)No risks involved

What Are The Optional Tests During Pregnancy?

Optional tests are performed on pregnant women who are at a risk of having a baby with a genetic disorder or congenital disability.

TrimesterOptional tests included
  • Cystic fibrosis
  • Chorionic villus sampling
  • Nuchal translucency screening
  • Multiple marker screening
  • Amniocentesis
  • Nonstress test
  • Biophysical profile

What Are The Recommended Prenatal Tests For Women Over 35?

Genetic screening tests are usually recommended for pregnant women over 35. It is because the risks of chromosomal abnormalities increase with advancing age. The usual tests the obstetrician recommends are cell-free DNA testing, chorionic villus sampling, nuchal translucency screening, amniocentesis, and anatomy ultrasound around the 20th week of pregnancy.

If results from these tests are abnormal, your doctor will refer you to a genetic counselor, who will help you understand the options and manage the condition.

Understanding Prenatal Tests And Their Results

If your healthcare provider recommends prenatal tests, you should ask the following questions and more.

  • Why do I require the tests?
  • What will the results say?
  • Is it compulsory to get the test?
  • How accurate are the tests?
  • How long does it take for the test?
  • What are the risks involved?
  • How much does it cost?
  • Is there insurance coverage?
  • Where should I get the tests performed?

Getting answers to these questions will help you learn about the test, and cope with any fears and worries that you may have.

Can You Refuse Blood Tests During Pregnancy?

You cannot decide whether you need a blood test or not. Schedule a separate appointment to discuss with your provider to help you make the right decision.

Frequently Asked Questions

1. What tests are done to identify abnormalities?

Amniocentesis, chorionic villus sampling, and non-invasive prenatal testing tests can help detect genetic abnormalities in the fetus (16).

2. What is the difference between screening and diagnostic testing for birth defects?

Genetic screening tests are done to determine whether or not the fetus is at risk of developing a genetic condition. On the other hand, genetic diagnostic tests are performed to identify or eliminate suspected genetic conditions in the fetus (17).

It is essential to undergo regular tests for each trimester during pregnancy. Each prenatal test helps ensure the well-being of the mother and the unborn baby. Blood pressure tests, urine tests, blood tests, and screening tests such as amniocentesis and prenatal ultrasounds are scheduled at various times during pregnancy. Doing the scheduled tests on time helps identify and treat or manage the conditions before complications arise. However, delaying the tests could cause the problems to go unnoticed for a long time and negatively impact fetal growth and development.


  1. Prenatal care and tests, OASH, Office in Women’s Health.
  2. Prenatal screening and testing, NIH.
  3. First-trimester screening, University of Rochester Medical Center.
  4. Chorionic villus sampling, University of Rochester Medical Center.
  5. What is non-invasive prenatal testing (NIPT) and what disorders can it screen for? MedlinePlus.
  6. Nestor N. Demianczuk and Michiel C. Van den Hof; (2003); The use of first trimester ultrasound.;jsessionid=09F6069FAA08A076D0FC6DC708EDDA73?doi=
  7. Nuchal translucency test, MedlinePlus.
  8. Amniocentesis, Children’s Hospital of Philadelphia.
  9. Fetal Blood Sampling, Children’s Hospital of Philadelphia.
  10. 2nd trimester Quad screen, University of Rochester Medical Center.
  11. What is level II ultrasound? Northwell Health.
  12. Guillermo Azumendi et al.; (2008); Ultrasonographic Evaluation of Fetal Face by 3D/4D Sonography.;jsessionid=A4DE1294B2283DD2125266CD5562248F?doi=
  13. Group B Strep: Fast Facts, CDC.
  14. Nonstress Test, Beaumont.
  15. Biophysical profile, Children’s Hospital of Philadelphia.
  16. Detecting Genetic Abnormalities; Healthy Children
  17. How are genetic screening tests different from genetic diagnostic tests?; MedlinePlus

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