Even if you’ve never had one before, you probably know exactly what a stress test is. When you’re an adult and your body is put under heavy amounts of stress from exercise or even emotional stress at work or home, your doctor needs to test your heart and make sure it’s responding properly. Often, you’ll see people running on treadmills in front of the doctor in depictions of this test in movies and other forms of media. This depiction is accurate, as exercise is a perfect way to measure heart function. Believe it or not, this same test exists for babies still in the womb. Obviously, a fetus won’t have access to a treadmill, so there is another method of testing heart function with the same intentions.

When you’re pregnant, your doctor will recommend a non-stress test for your baby. It’s called a non-stress test because—unlike the one for adults—the test doesn’t put any stress on your baby. To measure your baby’s heart function during activity, your doctor will attach two belts around your belly. One belt will measure activity and contractions while the other measures your baby’s heart rate. If your baby seems to be moving normally and his heart rate increases accordingly, the results will be considered non-reactive. These are the desired results, as they indicate normal heart and bodily function.

If your baby’s non-stress test results are reactive, it might mean that your baby is not getting enough oxygen. Further testing will be needed to determine exactly why, but it’s usually a result of problems with the umbilical cord or placenta. The role of both of these organs is to deliver nutrients and oxygen to the baby, so if his or her heart is not functioning properly, there might be a problem with either.

Your doctor will recommend a non-stress test if you notice that your baby is not as active as you’d expected, or if you’re overdue. It’s a good way to measure the general health of your baby since movement and heart rate are monitored and compared. The test is only performed after the 28th week of your pregnancy. Until that point, your baby’s heart rate and movement will be unrelated.

Stress tests for adults and non-stress tests for babies are generally the same. Of course, the methods for finding the results are totally different, but they’ll clue doctors into the same problems.

Source: Murat Kinas et al: The Role of Fetal Movement on Predicting the Non-Stress Test Results. The Journal of Turkish Obstetric Gynecology Volume 8 pp. 238-243 2011

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