8 common tests during the third trimester of pregnancy

8 common tests during the third trimester of pregnancy 

Your doctor may recommend certain diagnostic tests during the third trimester of your pregnancy to ensure the well-being of you and your unborn baby. You'll be offered many tests throughout your third trimester depending on your age, health, family medical history, and many other things. 

Common tests during the third trimester of pregnancy

The tests which are common and you might receive in the third trimester of your pregnancy are described below :

Group B streptococcus screening

Group B streptococcus (GBS) is a bacteria that can exist in the female reproductive tract. Around 30% of healthy women can carry GBS. However, it usually doesn't cause any problems but in some cases, it can lead to infections such as Urinary Tract infection, Placenta infection, or Bloodstream infection. It can also have serious consequences for the baby which causes life-threatening infections in the newborn such as Pneumonia, Meningitis, and Sepsis. Group B streptococcus screening is usually done between 35 weeks and 37 weeks of pregnancy. 

GBS Screening

During GBS screening a sample is taken from the vagina and rectum with a cotton swab. After that, this swab is cultured in the laboratory to find out if Group B strep is present. If the test is positive, your doctor will give you antibiotics during labor to reduce the chances of infection in the baby. Group B streptococcus screening will be done in a subsequent pregnancy, even if you get a negative result in your first pregnancy. 

Electronic Fetal Heart Monitoring

This test is done to monitor the heart rate of the fetus during pregnancy, labor, and delivery. The fetal heart rate signifies that the fetal is doing well or is in any trouble. Electronic Fetal Heart monitoring is usually done to ensure the baby's health. This monitoring can be done anytime after 20 weeks of pregnancy.


An ultrasound is a test that uses sound waves to make images that show your baby's position, size, and shape in the uterus. An ultrasound exam may be performed during the third trimester to examine the position of the placenta, monitor the baby's movements, evaluate fetal growth, and determine the levels of amniotic fluid. Pregnant women with high-risk pregnancies may have multiple ultrasounds during the third trimester. 

Glucose Screening

Glucose Screening checks for gestational diabetes. Gestational Diabetes is a short-term form of diabetes that develops in some women during pregnancy. If it is not diagnosed or treated properly it can cause serious infections in newborns. For this test, you'll have a sugary drink and then after an hour, your blood sample will be taken to check your sugar levels. 

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Non-Stress Test 

Non-Stress Test (NST) is used to measure the baby's heart rate as the baby moves. This test can be done anytime after 28 weeks of pregnancy but it is mostly done after 32 weeks of pregnancy. It is a non-invasive test which checks your baby's health by monitoring the baby's heart rate for a 20-30 minute period. This test is used to monitor overdue babies. This test is performed if a pregnant woman has diabetes, has high blood pressure, or carrying more than one fetus. If you feel your baby is not moving as usual NST may be ordered to ensure the well-being of your baby. NST is also done to ensure that your placenta is healthy and doing well. It is mostly done weekly in cases of high-risk pregnancies. 

Biophysical Profile

Biophysical Profile (BPP) is another test that is performed during the third trimester of pregnancy to check the baby's well-being. This test can be performed once or twice a week and it takes about 30 minutes. It combines the non-stress test with ultrasound.

  • Non-Stress Test 

The non-stress test portion of the Biophysical profile (BPP) involves giving a score to your baby for his/her heart rate depending on if it is reactive or non-reactive.

  • Ultrasound 

The ultrasound portion of BPP involves examine and measures four characteristics of fetal which are given below :

  • Baby's body movements
  • Baby's breathing
  • Baby's muscle tone
  • Level of amniotic fluid

Contraction Stress Test

In this test, a fetal monitor measures the baby's heart rate in response to uterine contractions which are elicited either by administering oxytocin (Pitocin) or by stimulation of the nipples. The blood flow to the placenta slows during contractions. If the placenta is doing well, the baby's heart rate remains stable and if the placenta is not functioning properly baby's heart rate will temporarily slow after a contraction. This test helps the doctor to estimate how the baby will respond to the stresses during labor. Contraction Stress Test is mostly done in high-risk pregnancies. 


Amniocentesis is usually done in the second trimester of pregnancy but in some cases, it is also performed later in pregnancy. During this test, a sample of amniotic fluid is removed with a long and thin needle. If there is a risk of premature delivery amniocentesis can determine whether the baby's lungs are mature or not. Infants born with immature lungs may develop Respiratory Distress Syndrome (RDS). RDS is a condition in which the lungs of infants can't inflate properly and the baby feels difficulty in breathing. 

Amniocentesis test

If an amniocentesis test shows that your baby's lungs are immature then your health care provider will recommend Corticosteroids. Corticosteroids are the drugs that help to speed up the development of the baby's lungs.

Don't forget that these tests are offered to you but it's your choice whether to have them or not. Talk to your health care provider to decide which tests are right for you. Also ask about the risks, benefits of the test, and the reason why it is recommended to you.

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    Disclaimer: This content is intended for general information only and should not be used as the basis of patient treatment. The given content is not intended to be a substitute for professional medical advice, treatment, or any diagnosis. Always consult a doctor for more information. Our website doesn't claim responsibility for this information.

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