Prenatal Testing: What is a Nonstress Test?


Expectant mothers always have this constant worry about their baby’s health, especially since congenital birth defects can possibly happen to some. Good thing there are prenatal screening tests that can be done, usually within the first and second trimesters, to rule out this possibility. Once a screening test shows a positive result, diagnostic tests will then provide a conclusive answer.

Some prenatal tests may be required for pregnant mothers as routine procedures, while others may be offered additional screening exams, especially those with higher risk of bearing a child with certain health conditions. One of these additional prenatal exams include a fetal nonstress test.

What to know about a nonstress test

Also known as a fetal heart rate monitoring, a nonstress test(NST) is a common prenatal exam to check on the baby’s health. The procedure involves a monitoring of the baby’s heart rate in response to his movements. The test is termed “non-stress” since it is noninvasive, meaning there is literally no stress placed on the fetus over the duration of the procedure.

During a nonstress test, the healthcare practitioner checks on the baby’s heartbeat on two occasions: while the baby is at rest and while he is moving. Normally, the baby’s heart rate increases when he is kicking or moving, just as our heart beats faster when we are active.

Nonstress test for high-risk pregnancies

Generally, the goal of a nonstress test is to evaluate the baby’s oxygen supply based on how his heart rate responds to his movements. But when is it really necessary?

Your doctor may recommend a nonstress test done if the mother is already past her due date, or if she is having a high-risk pregnancy a month or two leading up to her due date. Specifically, you may need to undergo a nonstress test if you have a pregnancy-induced high blood pressure, type 1 diabetes, or a heart disease.

You are also likely to need this screening test if you have had a history of complications during a previous pregnancy, Rh sensitization, oligohydramnios or a low amniotic fluid, or if your baby is shown to have decreased fetal movements or growth problems.

What to expect during an nonstress test

Before the procedure, the doctor may advise you to grab a meal to hopefully stimulate your baby to move during the test. It may also help to use the bathroom prior to the test, as you will remain strapped to a monitor for the next hour or so.

During the procedure, you will be asked to lie on your left side. Then, two fetal monitor pieces, an ultrasound transducer and a toco transducer, will be placed on your abdomen with elastic belts holding them in place. The ultrasound transducer measures your baby’s heart rate while the toco transducer keeps track of the uterine activity.The results of an NST may either be reactive or nonreactive. It is reactive if the fetal heart rate increases when the baby moves, which sho uld happen at least twice in 20 minutes. To stimulate the baby, the nurse may have you drink water or juice.

However, if the baby’s heart does not beat faster upon movement, or if he is not moving, the test will show a nonreactive result. But a nonreactive result should not be a cause of worry just yet as this could only mean the NST has not given enough information that you need. During such time, the doctor may recommend additional tests such as a contraction stress test or a biophysical profile to further check on the baby’s condition. Prenatal testingis important to ensure that the baby is growing and developing normally. Although such screening tests and procedures may indicate undesirable results, the good thing is that certain measures can be done promptly to guarantee a safe and healthy delivery of your child.

Authored by : Dr Aniruddha Malpani, MD and reviewed by Dr Anjali Malpani.