Why is a Non-Stress Test done during pregnancy?
What is a NST test in pregnancy ?
The non-stress test is used to assess the well-being of the fetus during the prenatal period.
This test is recommended when there is a history of pregnancy with complications or when factors that may increase the risk of morbidity/mortality in the fetus are identified during pregnancy. These risk factors may be present in the mother (insulin-dependent diabetes, blood pressure disorders, prolonged pregnancy of more than 41 weeks, twin or multiple pregnancy, etc.) or in the fetus (intrauterine growth retardation, decreased amniotic fluid, fetal malformations, etc.).
Decreased fetal movements are also a risk factor. If you notice
decreased movements in the unborn child, an assessment should be carried out by the healthcare team. A fetal reactivity test will be carried out if necessary.
Tests and procedures
The non-stress test (NST) simply requires that the pregnant woman has
emptied her bladder before the test. The test is performed in a semi-seated position or in a lying position, lying on the left side. The left lateral position, which promotes fetal-maternal circulation, is also preferred throughout pregnancy. The
lying position on the back is not recommended.
The test is performed using a fetal heart monitor. Two sensors are placed
on the abdomen: one is used to listen to and record the fetal heart rate while
the other evaluates and records the activity of the uterus (contractions).
The non-stress test is normally performed over a period of 20 minutes. Depending
on the responsiveness of the fetal heart rate, a longer period may be necessary. Throughout the test,
the healthcare team will interpret the tracing and extend it if
necessary. The test performed essentially evaluates the rhythm
of the fetus's heart and its periodic variations. The fetus's heart rate
varies between 110 and 160 beats/minute. It is normal to see it vary
between 125 and 150 beats/minute, for example. However, the fetus's heart rate
must not maintain the same rhythm: it must
present a certain variability as well as periods of acceleration.
Treatments and follow-ups
The frequency of the non-stress test depends on the progress of each pregnancy: it can be requested once during the pregnancy or several times a
week. Depending on the results obtained, other tests may be necessary to ensure the well-being of the unborn child.
