Nonstress Test : Purpose, Risks and Procedure

Overview

During pregnancy, the healthcare provider may recommend several prenatal tests necessary to check the health of the mother and the unborn child and detect any abnormalities. One of them is the non-stress test. 

As the name suggests, a nonstress test does not exert any stress on the baby and is non-invasive. The test monitors the baby’s heart rate when it moves. It also tests the oxygen level in the unborn child. Doctors recommend the non-stress test at the end of the pregnancy or early if it is a high-risk pregnancy. 

This blog provides a detailed understanding of a nonstress test, its purpose, risks and procedure.

What is a nonstress test?

As mentioned above, a nonstress test examines the baby’s heart rate and oxygen level when they move. Women can feel the baby’s movement at 16 weeks of pregnancy. As the pregnancy progresses, the baby becomes more active, and so does its heartbeat. A robust and healthy heartbeat indicates that the baby is getting adequate oxygen.

When the baby is not active, or if movements slow down, it can suggest that the baby is not getting adequate oxygen. In any pregnancy, the objective is to maintain the woman and the baby’s health. 

Typically, doctors recommend a non-stress test in the third trimester of the pregnancy if they believe there could be issues with the baby or if women are at risk for pregnancy complications. Therefore, women can get anxious when they undergo a nonstress test. Women at high risk undergo multiple nonstress tests during their pregnancies, as frequently as once or twice a week. With the help of an external monitor, doctors can monitor the baby’s heartbeat and movements and, in most cases, even identify uterine contractions. 

Why do women require a nonstress test?

Not every pregnant woman requires a nonstress test. They may have to undergo this test if they are:

• Overdue
• The baby’s movement is not normal
• Suffering from various health conditions such as high blood pressure, heart disease, diabetes, or a clotting disorder
• Having multiple pregnancies (twins, triplets, or more)
• Suffering from complications in a previous pregnancy
• Low levels of amniotic fluid

The doctors may also recommend this test if the pregnant woman’s blood group is Rh-negative. This condition can cause the woman’s body to produce antibodies in the baby’s blood.

How is a nonstress test performed?

Before the procedure

The doctors will take the pregnant woman’s blood pressure before the nonstress test begins.

During the procedure

A nurse performs a nonstress test with the obstetrician-gynaecologist interpreting the results. Throughout the test, the doctors check the pregnant woman’s blood pressure at different intervals. Women need to lie down on the examination table, a nurse applies a special gel to their abdomen, and attach a transducer around the stomach. A transducer is a monitor that analysis the baby’s heartbeat. A uterine monitor is also connected to the mother to evaluate and monitor any uterine contractions. 

Once the woman is connected to the external monitor, the women are given a buzzer to press whenever they feel the baby move.

The computer monitor receives the movement information every time there is a click or a buzz. When the baby is awake and active at the start of the test, the nonstress test can last only about 20 minutes. The test may take longer when the baby is asleep or inactive. In such cases, the nurse must wake the baby by placing a noise-making device over the woman’s stomach to wake the baby. Additionally, eating or drinking can wake the baby and keep them active.

After the procedure

When the nonstress test results are nonreactive, the doctor will suggest more prolonged monitoring, likely on the same day, or they can ask for additional tests.

The doctor can determine if the baby is under stress depending on the results of a second nonstress test or additional tests. At this point, women must discuss whether they must undergo further testing or if the factors, including gestational age, support their decision to induce labour.

When women have a high-risk pregnancy or expecting multiples, the doctors can perform many nonstress tests during the pregnancy, even if previous test results have been reactive. By doing this, the doctor can continue to examine the baby’s health for the duration of the pregnancy.

What do the results of the non-stress test mean?

The doctor provides one of the two results as follows:

• Reactive: If the test is conducted before 32 weeks of pregnancy and the baby’s heartbeat accelerates to a certain level above the baseline twice or more for at least 10-seconds each, within 20 minutes, it is known to be reactive. Similarly, if the test is performed after 32 weeks of pregnancy and the baby’s heartbeat accelerates to a certain level above the baseline twice or more for at least 15-seconds each, within 20 minutes, the results are reactive. 
• Nonreactive: when the baby’s heartbeat does not meet the above-said criteria, the results are considered nonreactive. It may be because the baby was inactive or asleep during the test. 

A reactive nonstress test is assuring to the mother. However, a nonreactive nonstress test may cause concern and lead to another prenatal test to check the baby’s health. The following are some of the tests recommended by the doctor:

• Biophysical profile: The doctor performs a biophysical profile along with a fetal ultrasound to evaluate the baby’s breathing, movements, muscle tone, and amniotic fluid level. 
• Contraction stress test: The test evaluates the baby’s heart rate when the uterus contracts. During the test, intravenous oxytocin is used to induce uterine contractions .

Conclusion

A nonstress test can make women anxious. It is required when women are at high risk or if they have had previous complications. Doctors can keep the woman and baby healthy with more information from prenatal tests. Most women who undergo nonreactive test results have delivered healthy babies. Therefore, there is no need to get anxious. 

Frequently Asked Questions (FAQs) 

1. Does a nonstress test have any risks?

The woman and the baby have no risk from a nonstress test.

2. What do the results mean?

The results of the nonstress test results mean one of the following:

• Reactive – these results indicate that the baby’s heart rate and movement are normal. It suggests that the baby is healthy, not under any stress, and its heart rate has increased with the movement.
• Nonreactive – if the test results are nonreactive, it indicates that the baby has not met the minimum number of movements as it should have. It can also show no change in the baby’s heart rate with movement. 

Women must not get anxious if the results are nonreactive. It can mean that the baby was asleep or not cooperative during the test, thus demonstrating less movement.

3. What additional tests can the doctors perform with a nonstress test?

In addition to a nonstress test, the doctor can perform a biophysical profile and a contraction stress test.

4. When should women get a nonstress test?

Doctors do not perform a nonstress test until the beginning of the third trimester, generally around 32 weeks. However, women can undergo this test early if it is a high-risk pregnancy.