Non-Stress Test

A non-stress test (NST) which is also known as fetal heart rate monitoring is a non-invasive test performed in order to examine the health of the growing fetus.

The test is called so because there is no such stress placed on the fetus while the test is carried out. The heart rate of the baby is monitored so that the baby’s movement can be checked.

This test is recommended when there is an increased chance of death of the baby and can also tell whether the mother and the baby need special care or not. Being a non-invasive test it will not pose any kind of physical risk to the baby.

Here are the most common reasons to undergo a non-stress test. In general, this test is performed to assess the health of the baby during pregnancy and its main aim is to provide the information regarding the oxygen supply to the baby.

This can be done by checking the heart rate of the baby and how this heart rate affects the movement of the baby. During pregnancy, the heart rate of the baby is much faster but in certain conditions like fetal hypoxia wherein, there is not enough oxygen for the baby, can lead to the interruption of the normal pathway.

The doctor may recommend this test to the patient under following conditions:

• If the women had multiple pregnancies along with some complications.
• If the mother is having any of medical condition like a heart disease, Type 1 Diabetes, or high blood pressure during pregnancy.
• Delay in the delivery may be two weeks post due date.
• Decrease in the movement of the fetus.
• Rh (rhesus) sensitization, which a condition where the blood group of the mother is Rh negative and the blood group of the fetus is Rh positive. This may occur when there is a second or subsequent pregnancy.
• Lower amount of amniotic fluid (oligohydramnios)

The doctor may recommend this test to be conducted once or twice a week and in certain conditions daily which is dependent on the health of the mother and baby. The doctor will suggest the mother to opt for the test daily if the baby is not getting enough oxygen.

Along with undergoing a non-stress test comes potential risks. This test is a non-invasive one and therefore, will not cause any physical damage to the baby and as the name suggests no stress is given to the baby.

Though the test suggests hope for the baby’s health, it may lead to anxiety. This test may not detect the existing problems or may suggest a problem which actually does not occur. In such cases, this may lead to further testing.

A non-stress test typically requires no special preparation.

Here’s what you can expect before, during, and after your non-stress test. The test is generally performed in a health care center. The process may be divided into three phases: 

Before the procedure, the doctor will check the blood pressure of the mother before conducting the test.

During the procedure, the mother will be lead onto a reclining chair and the blood pressure will be checked at regular intervals. The health care provider will place two belts around the abdomen and these belts will be attached to a monitor.

Among the two belts, one belt will analyze the heart rate of the baby and the second one will record uterine contractions the mother may experience. The doctor will tell the mother to notify him when the baby makes a movement and the baby’s movement will also be noted on the heart record.

The doctor will check the rate of the heart beat when the baby moves makes a movement. The test will take only 20 minutes but if the baby is in its inactive state i.e. when the baby is sleeping, the time may be extended with a hope that the baby will come to its active form.

This will ensure right results. In order to make the baby active the doctor may also try to wake him/her up manually or by using a device on the mother’s abdomen that produces noise.

After the procedure, the test is completed the doctor will discuss the results with the patient.

The results of the non-stress test can be categorized under two headings:

Reactive: The results are considered normal if before 32 weeks of pregnancy the heart rate of the baby accelerates to a level that is two or more times greater than the baseline and this may occur for 10 seconds each within 20 minutes.

On the other hand, the results are considered normal if at or after the 32 weeks’ of pregnancy, the heart rate accelerates up to a level that is two or more times greater than the baseline for 15 seconds each within 20 minutes.

Nonreactive: In this condition, the baby’s heart rate will not come under the criterion mentioned above and this may occur if the baby is inactive or sleeping.

There are certainly other factors that may result to non-reactive results and these factors may include:

• decreased oxygen (fetal hypoxia)
• maternal smoking
• maternal use of medications
• Fetal neurologic or cardiac anomalies

The doctor might recommend for delivery in case the test is extended to 40 minutes but is still nonreactive when the mother is at 39 weeks of pregnancy.

In case the mother is not at 39 weeks of pregnancy, the doctor may opt for other prenatal tests in order to examine the baby’s condition which may include the following:

Biophysical profiling: This test is done in combination with non-stress and involves ultrasound of the fetus to examine the movement of the baby, muscle tone, and finally to know the level of amniotic fluid.

Contraction stress test: This test is done in order to check for any change in the heart rate of the baby when the mother suffers uterus contractions.

If there is not sufficient uterine activity during contractions then the doctor will give intravenous oxytocin to the mother or may ask her to rub her nipples in order to induce uterine activity.