A Non-Stress Test (NST) is a routine prenatal screening used to assess fetal well-being during pregnancy. This non-invasive procedure monitors the baby’s heart rate patterns, providing insights into their health. It helps healthcare providers check on the baby, particularly in the third trimester, to ensure adequate oxygen supply.
Understanding the NST Procedure and What it Measures
The NST takes about 20 to 30 minutes. During the test, the pregnant individual reclines comfortably while two belts are placed around their abdomen. One belt measures the baby’s heart rate, and the other monitors for uterine contractions. A special gel is applied to the skin to help the monitors work effectively.
The primary purpose of the NST is to observe the baby’s heart rate in response to movements. A healthy baby’s heart rate increases with activity, similar to an adult’s. The test also looks for the absence of concerning decelerations, which are drops in the heart rate. These measurements indicate the baby’s oxygenation and overall health. If the baby is not moving, it might be asleep, and a small buzzer-like device can be used to gently wake the baby to encourage movement.
Interpreting NST Results
NST results are classified as “reactive” or “non-reactive.” A reactive NST indicates adequate blood flow and oxygen supply to the fetus. For a test to be reactive, the baby’s heart rate must show at least two accelerations within a 20-minute period. Each acceleration should be at least 15 beats per minute (bpm) above the baseline heart rate and last for at least 15 seconds.
A non-reactive NST means the baby’s heart rate did not meet the criteria for a reactive test. This does not automatically signify a problem, as babies can be in a sleep cycle or certain maternal medications might influence results. However, it indicates a need for further evaluation to determine the reason for non-reactivity. Other patterns, such as decelerations in the heart rate, may also be observed and prompt closer investigation.
What Happens After an NST
Following an NST, the course of action depends on the results. If the test is reactive, indicating a healthy fetal response, no immediate further action is required. This result suggests the baby is receiving enough oxygen and is doing well.
If the NST is non-reactive, it leads to additional testing rather than immediate intervention. This is because a non-reactive result can occur for various reasons, including the baby being in a sleep cycle, and does not automatically mean there is a problem. Common follow-up tests include a biophysical profile (BPP), which combines an NST with an ultrasound to assess breathing, movement, and amniotic fluid levels, or a contraction stress test (CST), which observes the baby’s heart rate response to contractions. These additional assessments help gather more comprehensive information about the baby’s well-being.