The foetal Non-stress Test (NST) is a form of optional medical investigation performed during pregnancy. Your doctor will recommend this test to you when he will consider it right and useful. It is usually performed in the last trimester (after week 29) and it evaluates the baby’s state (it is recommended before due date or when the due date is exceeded).
The Non-stress Test is a risk-free and “stress”-free investigation for your pregnancy and your baby (unlike other procedures, such as amniocentesis or chorionic villus sampling – CVS), and is a relatively simple and non-invasive procedure. The test consists of monitoring the baby’s heart rate during his active moments (when he moves in-utero). The test is mainly based on the fact that, when the baby is sleeping, his heart rhythm slows down, but it becomes faster when the baby is active. The basic idea is that if the heart rate is not regular and does not get faster when the baby is moving, there may be some risks involved – the baby does not get enough oxygen through the umbilical cord, which is why the heartbeats do not increase once the activity intensifies.
How the foetal Non-stress Test (NST) is performed
Usually, the foetal Non-stress Test during pregnancy is part of the contraction stress test: this test is combined with a thorough ultrasound and the result shows the foetus’s heart rhythm and movements, as well as the amount of existing amniotic fluid. The Non-stress Test is performed by attaching a belt on the mother’s belly (instrument which monitors the baby’s heartbeats and movements), while another belt will observe the uterus’ contractions. If no movement is recorded, you will be asked to drink cold water in order to wake the baby or, in some cases, the doctor will wake him up (it is also advisable to eat right before having the test).
The tests results are based on the way the baby reacts – when it moves, there is an increase in the number of heartbeats, which means that the baby is healthy. If the baby does not move for half an hour or if his heartbeats are slow while moving or while you are having a contraction, there is the possibility that your baby is suffering and a contraction stress test is recommended (this implies performing the Nonstress Test again, this time combined with an ultrasound). Foetal suffering can be related to an insufficient amount of oxygen (a reduced heart rhythm during contractions or while moving indicates a lack of oxygen); the Non-stress Test is a procedure that might make the doctor decide on inducing labour, if the sign of foetal suffering are confirmed.
The foetal Non-stress Test (NST) is not a routine medical test, but it might become very useful in some pregnancies. It is considered to be necessary at regular times until due date. It is mainly performed in the following situations:
- The baby is not active, so he does not move regularly in-utero (the future mother can see if the baby is active enough or not – after she starts feeling the baby’s movements, she might be able to realize if there is something wrong with his movements);
- The baby cannot keep up regarding normal growth and development;
- The baby has a congenital defect;
- The future mother suffers from hypertension or diabetes (or other disorders that present risks for a pregnancy and imply risks after risky medical investigations, such as amniocentesis – after the procedure, one needs to see if the baby has been affected);
- The mother-to-be has had a miscarriage in the past;
- There is not enough amniotic fluid;
- The due date has been exceeded and the baby’s general state must be checked ( in order to see if he gets enough oxygen).
Therefore, the fetal Non-stress Test (NST) aims at verifying the baby’s state (especially before the due date or if the due date has been exceeded). It does not indicate the existence of a problem with absolute certainty– if the fetus’ heart rhythm does not respond properly to movement or to the mother’s contractions, the test will be performed again, together with other procedures. The pregnancy will be closely monitored – the test will be performed at a regular basis, and if further medical investigations show that the fetus has problems, labor will be induced by performing a C-section.