In my article on this web site titled, “Is My Baby Okay?: Detecting Fetal Movement,” I talked about the importance of counting fetal movements as an indicator of your baby’s health in the last month of pregnancy. In this article, I focus on a simple test we perform to asses your baby’s health in the third trimester. It is called the nonstress test, or NST. This test is a very good indicator of the baby’s health and is usually completed within 30 minutes.

The NST is performed when there is concern for the baby’s well being. Some common reasons to do the test include:

• Reduced fetal movement
• Mother has high blood pressure
• Mother has diabetes
• Mother is experiencing medical complications of pregnancy, such as heart or kidney disease
• Expecting twins, triplets or more
• Baby is growing slowly
• Mother had a prior stillborn delivery
• Baby is overdue

The nonstress test is performed in a doctor’s office, outpatient testing center or labor and delivery unit. The test entails placing an ultrasonic transducer on the mom’s abdomen and recording the baby’s heart rate on a fetal monitor. Each time the baby moves, the woman will push a button, registering the baby’s movement on the recording strip. Ideally, the baby’s heart rate will accelerate during this time. In total, the test is complete when the baby has had at least two episodes where its heart rate has gone up from its resting rate by 15 beats for 15 seconds within a 20-minute time-frame. This is considered a reactive test. If the baby is unable to accomplish this on the monitor, it is called non-reactive.

We know that babies spend 50% of the time resting. They will not pass the NST during this time. In this situation, we will try to wake the baby by using an acoustical stimulator (a quiet alarm clock), or having the mom drink water or eat something sweet while we continue to monitor the baby. Each of these tricks can convince the baby to stretch out and show us its stuff. A reactive test is a good sign that the baby is receiving plenty of oxygen and nutrition. It should do well over the next week.

But not all babies respond to our tricks, and continue to have a non-reactive nonstress test. This does not mean the baby is in stress. Rather, it is a wake-up call for the doctor to do further tests to make sure the baby is healthy.