How to read an NST

Written by emer o'broin | 13/05/2017
How to read an NST
Monitoring the contractions. (Jupiterimages/ Images)

An NST is a "Non Stress Test" for pregnant women. It is generally taken if the pregnant woman has a health issue such as diabetes, or if the baby is not growing. It usually takes about 30 minutes to an hour to complete. It measures the baby's heartbeat to see if it is working properly. If the baby is active the heartbeat should be normal. This test is done to see if there are any abnormalities with the baby and is also used for babies past their due date. Reading the results is simple once you know what the graph means.

Fetal heartbeat

The heartbeat of the baby is measured on the top line of the chart. The pregnant woman clicks a button when the baby moves which records the movement as a wavy line. If no movement is recorded it does not mean that something is wrong with the baby -- it could mean that the baby is asleep. If the baby is not moving after the doctor has prodded the woman's belly, this could be a sign that the baby is not receiving oxygen.


The bottom line of the NST shows the woman's contractions. A monitor called a tocodynameter is used to measure the rate of contractions. A belt is strapped to the woman's uterus. This line can record no movement and appear flat if the belt is not on properly or if the woman has moved. The line shows how many contractions are happening. If there is a problem with the contractions, this could impact on the baby. If the baby is overdue, birth may have to be induced.


If the results show a wavy line along the top of the graph, this indicates that the baby was moving and heart beat was recorded. A healthy heartbeat should be 15 beats per minute over the baby's resting rate. If a movement is recorded, this is known as "re-active." This is a good sign and means that the baby's heart is healthy. This result is the desired outcome as it means there are no health problems for the mother or baby. If the mother is having contractions, the bottom line should be wavy and shows how many contractions she's had. If there is movement on this line the result is "re-active," showing that the mother's contractions are normal.


If the top line on the graph is not moving, this could indicate that the baby is not getting enough oxygen or is asleep. It could also mean that the test was not recording the baby properly due to the movement of the pregnant woman. The baby should move if the mother eats before the test. If a result is shown as "non-reactive" the midwife might induce labour as conditions in the womb may not be good. If the line at the bottom of the graph is not moving, this could mean that the mother's contractions are abnormal and need to be checked.

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