Stress test pregnancy explained: When it’s done, why it’s needed, and what it means

Fetal heart rate monitoring is a method of checking the rate, rhythm, and  presence of the fetal heartbeat. 

A pregnancy stress test checks your baby’s heart rate to see how well it is in the womb.

It’s not emotional stress or pregnancy testing. 

This article explains what a pregnancy stress test  is, when it’s done and why doctors recommend it.

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What Is a  Pregnancy Stress Test ?

A pregnancy stress test is a medical test that monitors how your baby’s heart responds to movement or contractions. It assesses oxygen supply and overall fetal well-being.

A pregnancy stress test focuses on the baby, not the mother’s emotions. It looks at heart rate patterns, rhythm, and changes around a baseline. A healthy fetal heart rate usually ranges from 110 to 160 beats per minute.

There are two main types of pregnancy stress testing used in prenatal care.

• The Non-Stress Pregnant Test
• The Contraction Test

Non-Stress Test in Pregnancy

A non-stress test, often called an NST, is a simple, non-invasive test that checks your baby’s heart rate without putting the baby under external stress.

This test is typically done after 28 weeks of pregnancy. No contractions are induced. The goal is to see whether the baby’s heart rate increases with movement, which is a sign of good oxygen supply and nervous system health.

The test lasts 20 to 30 minutes.

If the baby does not move, it does not automatically mean there is a problem. The baby may simply be asleep. A small buzzer may be used to initiate movement.

A healthy result shows the heart rate rising at different times.

Contraction Stress Test in Pregnancy

A contraction stress test, or CST, checks how your baby’s heart rate responds during uterine contractions.

Contractions are gently initiated using nipple stimulation or Pitocin. 

During contractions, the baby’s oxygen and blood supply briefly drops. Most babies tolerate this well,  while others do not.

If the heart rate stays low after contractions, it may suggest the baby could struggle during labor.

This test is usually done after 32 weeks in higher-risk pregnancies and can be done more than once. This will help the provider track the progress of the baby over time and find problems or things that are not normal.

A negative CST result is reassuring and predicts good tolerance of labor. A positive CST may indicate a higher risk of fetal distress and often leads doctors to recommend closer monitoring or delivery.

How a Pregnancy Stress Test Is Done 

1. Monitoring

Fetal heart rate and uterine contractions are monitored with belt sensors on the abdomen.

2. Stimulation

Contractions are induced by giving Pitocin (synthetic oxytocin) or via nipple stimulation, causing the body to release oxytocin.

3. Observation

Doctors watch the baby's heart rate. A healthy baby's rate stays steady or increases; a stressed baby's rate slows down. 

Why Do Doctors Perform Stress Tests During Pregnancy?

Doctors use stress tests during pregnancy to protect the baby and guide care decisions. They do this via the following reasons:

1. To monitor the baby’s oxygen supply: Poor recovery of heartbeat after contraction signals reduced oxygen supply. This helps doctors make decisions regarding delivery and labor.

2. To check placental function: The test can indicate if the baby is not receiving enough oxygen because of placental or umbilical cord problems.

3. To detect signs of fetal distress 

4. To assess fetal well-being because low oxygen supply can affect other functions in the baby, especially neurological functions.

5. It also helps to decide whether labor is safe or if early delivery or cesarean section is needed.

When is a stress test done? 

Most pregnancy stress tests are done in the third trimester, usually after 32 to 34 weeks.

Doctors may recommend testing earlier or more often if certain risk factors are present, such as 

1. If there is reduced fetal movement, which might indicate lack of energy. 

2. If it’s a high-risk pregnancy, such as in health conditions like diabetes and high blood pressure.

3. If there vehave been complications in a prior pregnancy to avoid recurrence.

4. If pregnancy has lasted more than 40 weeks (overdue).

5. If it’s a multiple pregnancy with certain complications.

6. If you are Rh negative, because an Rh positive fetus will cause your body to produce antibodies against it. This can be very harmful in subsequent pregnancies.

Can Stress Cause a Negative Pregnancy Test?

Emotional or physical stress does not cause a negative pregnancy test.

Pregnancy tests detect the presence of the human chorionic gonadotropin hormone and it appears after implantation. Stress does not block or reduce hCG production.

However, while stress does not affect test accuracy, it can delay ovulation or periods. This can cause someone to test too early.

• If ovulation happens later than expected.

• Implantation happens later.

• hCG rises later.

Early testing may show a negative result.

This timing issue often leads you to think that stress probably caused the negative test.  However, the real culprit is testing too soon.

When to Talk to a Doctor

You should contact your doctor if 

• Stress testing during pregnancy makes you anxious.

• Pregnancy tests remain negative despite symptoms.

• Fetal movement decreases.

• You are not certain about test results or recommendations.

Conclusion

The pregnancy stress test is a trusted medical device used to measure the baby's heart rate, rhythms, oxygen, and strength to know if it can handle labor. 

Stress tests during pregnancy are usually considered safe for both mother and the child.

The tests are closely monitored and only recommended when necessary. 

Contractions, though stimulated during the CST, are mild and controlled. 

The healthcare providers carefully observe for any signs of distress and immediately stop testing if need be. The stress tests are non-harmful for babies and do not induce labor.

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