If you’ve had pregnancy complications or are considered high-risk, your doctor may suggest a variety of tests to determine your baby’s health.
One of the recommended tests could be a nonstress test during pregnancy or a pregnancy stress test. In some cases, a baby’s heart rate slows down too much to handle contractions, putting you at risk for pregnancy loss. The results from such tests can help your doctor decide whether immediate or early labor or a C-section is safest.
In this post, we’re telling you everything you need to know about nonstress and contraction stress tests.
Non-Stress Test Pregnancy and Biophysical Profiles (BPP)
Before considering a contraction stress test (CST), a doctor will typically perform a nonstress test, or biophysical profile (BPP).
A BPP uses both fetal heart rate monitoring (nonstress test) and ultrasound to measure and monitor a series of factors. To start, a doctor may first recommend a nonstress test. If your baby’s heart doesn’t react as expected, they may suggest a full BPP.
Unlike a CST, a BPP does not trigger contractions, making this test safe and noninvasive. With that being said, it’s not clear whether this test actually improves pregnancy outcomes. However, it may help a doctor decide when to deliver a baby and if a C-section is safer.
A BPP monitors fetal heart rate and ultrasound to test:
- Heart rate
- Muscle tone
- Amniotic fluid
Based on this information, your doctor will score each criterion. If you have a low score, your doctor may suggest additional testing, possibly including a contraction stress test. Sometimes, immediate or early delivery is recommended. Like CSTs, BPPs are usually done after week 32 but can be done earlier because they don’t pose any physical risk.
A biophysical profile may be recommended if:
- You’re experiencing pregnancy complications
- You have a history of pregnancy complications or pregnancy loss
- You have specific medical conditions (such as high blood pressure or heart disease)
- You’re two weeks past your due date
- Your baby is having growth problems
- There’s decreased fetal movement
- You have an abnormal amount of amniotic fluid
- You’re over 35 or obese
How a Non-Stress Test Pregnancy BPP Works
If your doctor has suggested a biophysical profile, you can expect two parts: The nonstress test (for fetal heart rate) and the ultrasound exam (to monitor additional factors).
For the non-stress test:
- You’ll lie down with a belt across your stomach to monitor fetal heart rate.
- You may be told to wait until your baby is awake so results are accurate. Alternatively, the doctor may try to wake your baby with sound.
For the ultrasound exam:
- You’ll lie down and the technician will apply a small amount of gel on your abdomen.
- They’ll roll a small ultrasound device over your skin.
- They’ll monitor the criteria listed in the previous section.
- If your baby is sleeping, this process may take longer.
A full biophysical profile usually takes about 30 minutes. Depending on your condition and results, your doctor may recommend additional BPPs. These may be done once or twice a week.
What are Contraction Stress Tests During Pregnancy?
A contraction stress test (CST) is a test some women take nearing labor to help predict how their baby will handle contractions. CSTs are usually reserved for women with complicated pregnancies when the doctor isn’t sure how the fetus will cope with contractions. When you have a contraction, your baby’s blood and oxygen supply drops. Although this usually doesn’t pose an issue, some babies experience a slower heart rate. This could result in labor complications or pregnancy loss. To prevent this, doctors test your baby to learn the safest options or interventions.
CSTs are done at 32-34 weeks or later. Undergoing one before that may pose additional risks.
CSTs were more common in the past, although they are still performed today. Most of the time, a woman will undergo a nonstress test or biophysical profile. If the results of these show a cause for concern, a doctor may recommend a contraction stress test to learn more. A CST will provoke contractions and then measure how your baby’s heart changes. If her heartbeat remains normal, that likely signals a baby healthy enough for labor.
What Happens During a Pregnancy Contraction Stress Test?
If your doctor recommends a CST, here’s what you can expect:
- You’ll lie down and have two belts around your stomach: One to detect fetal heartbeat and the other to measure contractions.
- You’ll then trigger contractions. To do this, you may massage your nipples through your clothing. This action is known to release your body’s natural oxytocin. The doctor may also give you the drug oxytocin through an arm IV. This is why the test is sometimes also called an oxytocin challenge test.
- The belts will measure your baby’s heartbeat and your contractions.
- This test typically takes about two hours.
When looking at the results of your pregnancy stress test, your doctor is considering two major things:
- Whether your baby’s heart rate drops during contractions (signaling potential problem)
- Whether your baby’s heart rate stays normal throughout (signaling a healthy baby)
If your baby’s heart rate drops, your doctor may suggest more testing. If results of those aren’t favorable, they may recommend early delivery as the safest option.
Even if the fetal heart rate is normal, if there’s other signs pointing to potential issues, your doctor may suggest you take the test again at another time.
Keep in mind that a contraction stress test is better used to rule out issues, rather than diagnose them. For example, some women have unusual results on another test but after a CST, they discover their baby is actually healthy. This is why, if problems are confirmed, additional tests are typically needed.
The Pros and Cons of a Pregnancy Contraction Stress Test
Before going ahead with a recommended CST, your doctor will go over the pros and cons to help you decide.
- Helps predict how baby will cope with contractions
- Can help rule out issues and let you know your baby is healthy
- Can signal whether early delivery is safest to prevent pregnancy loss
- If you’re worried about the drug oxytocin, you may be able to trigger contractions by massaging your nipples instead
- CSTs are usually safe (see risk section)
- Unlike many tests, it lasts two hours
- Contractions can make you feel uncomfortable
- CSTs can sometimes trigger early labor
- The test is riskier for some women (see risk section)
- You may need to take the test additional times
- Oxytocin, the drug used to induce contractions, is also commonly used to induce labor. However, some people may worry about unnecessarily introducing a strong drug into their pregnancy because there’s “no controlled data” available in human pregnancy.
Contraction Stress Test Risks
Although the test may be recommended by your doctor, it doesn’t mean it’s without risk.
For some women, a CST can trigger early labor. This could be more true for women who:
- Are at a higher risk of uterine rupture
- Have placenta previa
- Had a previous C-section
Considering these risks may sound scary. However, if your doctor has suggested a CST, it’s probably because they think the benefits will outweigh the risks. Put simply, if you have a complicated pregnancy, knowing how your baby will cope with contractions may be crucial to her health—even if there’s other risks involved.
If you’re worried about a suggested test, ask your doctor to go through the benefits and risks with you. Ultimately, it’s your choice whether you go through with it.
Summary of Stress and Non-Stress Tests (Pregnancy)
If your pregnancy is high-risk, there’s a good chance your doctor will recommend a non-stress test. This involves monitoring your baby’s heart rate. If the results aren’t favorable, a biophysical profile (BPP) may be suggested. This noninvasive test monitors a list of criteria, giving each a score. If your score is low, it could mean that your baby may have trouble withstanding the stress of contractions. In this case, your doctor will likely recommend additional tests, one possibility being a contraction stress test (CST).
A CST triggers contractions while monitoring how your baby’s heart rate responds. It’s a longer, more invasive test. Your doctor will weigh the benefits and risks. Results from a CST could rule out an issue or lead to additional testing. It could also help your doctor decide whether early delivery or C-section is safest.
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