A Non-Stress Test (NST) is a common prenatal assessment used to monitor a baby’s well-being during pregnancy. This non-invasive procedure helps healthcare providers assess fetal health without posing any risk to the mother or fetus. It provides information about fetal oxygenation and overall status.
What is an NST and Why is it Done?
A Non-Stress Test monitors the baby’s heart rate in response to their movements. The primary purpose of an NST is to assess fetal oxygenation and well-being by observing increases in the baby’s heart rate, known as accelerations. These accelerations indicate that the baby is receiving sufficient oxygen.
Healthcare providers recommend an NST for pregnancies requiring closer monitoring. Indications include pregnancies extending beyond the due date, a decrease in the baby’s usual movements, or maternal health conditions like gestational diabetes or preeclampsia. NSTs help monitor the baby’s well-being as pregnancy progresses.
The NST Procedure: What to Expect
During an NST, you will recline in a chair or on an examination table. Two specialized belts are placed across your abdomen. One belt contains a transducer that monitors the baby’s heart rate, while the other tracks uterine contractions.
The test usually lasts between 20 to 40 minutes. You may be given a button to press whenever you feel your baby move, which helps correlate fetal activity with changes in heart rate on the monitor. This allows healthcare providers to observe your baby’s patterns.
Interpreting Your NST Results
The results of an NST are classified as either “reactive” or “non-reactive.” A reactive NST indicates good fetal health. This result means that within a 20-minute period, the baby’s heart rate showed at least two accelerations.
For pregnancies at or beyond 32 weeks, an acceleration is defined as an increase in the fetal heart rate of 15 beats per minute (bpm) above the baseline, lasting for at least 15 seconds. For pregnancies earlier than 32 weeks, an acceleration may be defined as an increase of 10 bpm for at least 10 seconds. The baseline heart rate typically ranges between 110 and 160 bpm, with moderate variability, which are small fluctuations indicating a healthy nervous system.
A non-reactive NST means the test did not meet the criteria for a reactive result, showing fewer than the expected number of accelerations within the testing period. A non-reactive result does not automatically mean there is a problem with the baby. A baby might be in a sleep cycle or less active during the test, which can lead to a non-reactive outcome.
Factors such as certain medications or the baby’s sleep state can influence the results. In such cases, the healthcare provider may extend the monitoring period or suggest further evaluation. Medical professionals interpret NST results, considering all aspects of your pregnancy.
Beyond the Test: What Happens Next?
If your NST results are reactive, indicating your baby is well, usually no immediate additional action is necessary. Your healthcare provider will determine if and when another NST or other routine prenatal assessments are needed based on your individual pregnancy plan. This often means continuing with regular prenatal care appointments.
When an NST is non-reactive or inconclusive, further steps are taken to gather more information about the baby’s well-being. This might involve extending the monitoring period beyond the initial 20 minutes, sometimes up to 40 minutes, to allow for a change in the baby’s sleep-wake cycle. Alternatively, your provider may recommend a biophysical profile (BPP) or a contraction stress test (CST).
A BPP combines an ultrasound with an NST to assess fetal health, including movement, breathing, and amniotic fluid volume. A CST involves monitoring the baby’s heart rate during mild uterine contractions to see how they tolerate the stress of contractions. These follow-up tests help guide the next course of action.