Contraction Stress Test in Pregnancy: Procedure, Risks & How to Prepare

Contraction Stress Test During Pregnancy – Purpose, Procedure and Risks

During the third trimester, your baby is going to be growing faster, putting on more weight and causing you to feel very tired during this time as your baby is also going to be more active, opening and closing his eyes and moving around in your womb. There are times when you may even find yourself short of breath, but this is all perfectly normal in a healthy pregnancy.

The ninth month is a time filled with a lot of activity as the date of the big day draws near. There are a lot of tests that you are still going to need to undergo in order to keep a track of your baby and to ensure that there is no need for any medical or emergency intervention. The hope is that everything will be checked out and that you will be cleared for normal delivery.

The Contraction Stress Test is just one of the tests that you will need to undergo. Some of the other tests include the foetal heartbeat check; blood pressure check-ups; uterine screenings, urine tests and weight monitoring. In fact, it is only at the recommendation of your doctor that you should consider having the Contraction Stress Test done as some of the other tests available come with few risk factors as compared to this one.

What Is the Contraction Stress Test?

Also known as the Oxytocin Challenge Test, the Contractions Stress Test is done in order to see how well your baby will do during labour by measuring the heart rate of your baby during contractions.

When you are having a contraction, there is a drop in the oxygen and blood supply from the placenta to your baby. While most babies do not have a problem with this, there are some that are unable to cope with the stress, meaning they will not do so well during labour. If your baby’s heart rate goes back to normal after the induced contraction, then there is nothing to worry about, but if it slows down, it is a sign that your baby may not be getting enough oxygen from the placenta, and this may cause distress.

During this test, uterine contractions are induced by the administration of the oxytocin hormone if you are unable to have a contraction otherwise. The external foetal monitor, which is included in the test, shows changes in your baby’s heart rate.


Why Is Foetal Contraction Stress Test Performed?

The Foetal Contraction Stress Test is done in order to see if your placenta is healthy enough to support your baby and if your baby is getting enough oxygen from it during a contraction. Another reason you may have to get a test done is that the result of your non-stress test or biophysical profile may be abnormal.

How to Prepare for This Test

Arriving at the doctor’s office unprepared is not a good idea as there are certain conditions your body needs to meet in order to get the most accurate results. Here are the steps you need to take before you can undergo this test:

  • It is best not to eat or drink for at least four hours before the test is done. Eight hours is preferable.
  • Your doctor will request that you empty your bladder before the start of the stress test.
  • Smoking is very dangerous for your baby, and pregnant women should not be indulging in the habit. However, if you have been unable to stop smoking during your pregnancy, it is advised that you avoid smoking for two hours before you have the test done.
  • It is always best to speak to your doctor about the risks that will be involved during the testing process and make sure you settle all your doubts with him beforehand. Make sure your doctor explains to you exactly why the test needs to be done.
  • As there may be risks, you will need to sign a consent form saying that you understand the risks that are involved and agree to have the test done.

Oxytocin Contraction Stress Test Procedure

The Oxytocin Contraction Stress Test must be done by an obstetrician and a professionally trained nurse and lab technician. Here is the step by step explanation of how this procedure is most likely to go:

  • You will be asked to lay down with your back raised and tilted to the left a little in order for there to be no pressure on the blood vessels that are present in your belly.
  • Two sensory belts, the pressure gauge and the ultrasound transducer, will be placed around your tummy. In some cases, the gel is applied to your tummy to help the sound waves move directly from the ultrasound transducer head to the skin tissue. The ultrasound transducer monitors your baby’s heart rate, while the pressure gauge will measure your contractions.


  • The data recorded during the procedure is translated into two separate lines that appear on a graph.
  • An IV will be used to give you the oxytocin hormone. At first, it will be a low dosage, but it will be increased until you are having three contractions within ten minutes. Each of these should last from between forty seconds to sixty seconds, and they need to be as strong as the contractions experienced in the first stage of labour.
  • Your contractions and your baby’s heart rate will be monitored for around ten minutes along with your blood pressure and other vitals. The doctor may advise you to stimulate your nipples as this causes the release of natural oxytocin.
  • After the stress test, you will be observed until the contractions stop or go back to being how they were before the stress test. The test can take up to two hours to complete.

Do You Feel Any Discomfort or Pain During the Test?

While it may sound like the test will be a very painful experience for you, it is not usually the case at all. Here are things that you will feel as the test is in progress:

  • The belts that are placed across your abdomen may cause you some discomfort.
  • You will have a feeling that is very similar to menstrual cramps, though this is not supposed to feel painful.
  • The entire test may make you feel very uncomfortable.

Are There Any Risks Associated With This Test?

As stated earlier and like most medical procedures, this one comes with a few risks that are well worth noting. They are as follows:

  • There are instances that your uterus could be hyper-stimulated and the blood flow to the baby may be completely cut off due to extremely strong and frequent contractions.
  • The test can stimulate preterm labour if too much Pitocin is used too fast, though this may differ from woman to woman as not everyone has the same level of sensitivity to the drug.
  • Nipple stimulation is not preferred by most doctors as much as the administration of the oxytocin hormone as it is these contractions that can cause uncontrollable contractions that may result in premature labour.


When Is the Contraction Stress Test Not Recommended?

The contraction stress test is not recommended to those who have placenta previa (where the placenta blocks the birth canal) or if you are already highly likely to go into preterm labour, if you currently are at risk of premature membrane rupture or if you have had a  caesarean section during your previous pregnancy. So any high risk is a contraindication. In these cases, the following are recommended instead:

1. Non-Stress Test

A foetal non-stress test is performed once a week once you reach your ninth month or 38th week of pregnancy. This test uses the same two belts that are used during the Contraction Stress Test, except it does not use any stress or induce contractions.
Your contractions and the baby’s heart rate will be monitored over a period of twenty to thirty minutes. The reactivity of your baby’s heart rate to movement will also be measured. If the baby’s heartbeat is high for at least fifteen seconds, then it is considered to be normal.
The test should be done twice and should be at least twenty minutes apart from one another. Sometimes there may be no movement or very little movement; this could simply mean that your baby might be asleep. In this case, the nurse may use a buzzer method to wake the baby up.

2. The Foetal Ultrasound

These ultrasounds use high-frequency sound waves that are inaudible to the human ear. The echoes are shown as a video or photographs of your baby. Birth defects and any abnormalities are also shown during the ultrasound, which is why it is a preferable way of identifying what may be causing your baby to become distressed.
As foetal ultrasounds are pretty low risk and provide a wealth of information on the health status of the baby, it is highly recommended. Here your baby’s head, spine, heart and other body parts are examined to determine your baby’s condition. There are three types of foetal ultrasounds that you can opt for. These include the standard ultrasound, which uses sound waves to capture a two-dimensional image of your baby; the Doppler Ultrasound, which shows the movement of blood between the baby and the placenta as well as the baby’s heart; and the 3D ultrasound, which shows a three-dimensional image of your baby.


Reading the Contraction Stress Test Results

If your baby’s heart rate seems to drop after one of your contractions, this is not a good sign, and it is more likely that your doctor will then recommend further testing to be sure about if there is a real problem or not. While this test can show your baby’s health for up to a week, sometimes the results that it shows may be inaccurate, showing a problem when there isn’t one. This happens in around thirty per cent of women who have this test done.

The Contraction Stress test seems to be better at ruling out any problems you may have than actually diagnosing them. A lot of women who have had unfavourable stress test results have gone on to deliver perfectly healthy babies.

Here are the two possible outcomes and the contraction stress interpretation :

1. Positive Contraction Stress Test

If your baby has an abnormal test result, the result will be shown as a “positive”. After one of your contractions, your baby’s heart rate will decrease, and it will remain like that. If this happens on more than half of the tests that have been performed it is an indication that your baby may have problems during normal delivery.

2. Negative Contraction Stress Test

If your baby has a normal test result, then it is called a “negative” result. There may be times when your baby’s heart rate may seem like it is dropping, but as long as it doesn’t stay like that, it isn’t a big problem. If your baby can withstand three contractions in a ten-minute time span, without there being any worrying drops in heart rate, then your baby will definitely be able to withstand the pressure and stress that normal delivery is likely to cause.

Situations Which Can Affect the Results of the Contraction Stress Test

There are some things that will affect the results of your contraction stress test and make sure your doctor advises you to avoid it. They are as follows:

  • If you have previously had problems with your pregnancy and have had to have a classical caesarean section with the vertical cut, also known as a midline, you should avoid getting this test done.
  • If you have had any uterine operations, it is better to avoid this test as very strong contractions could cause the uterus to rupture.
  • If you have chosen to continue to smoke or suffer from any kind of drug addiction (like cocaine, for example), it is preferable that you should not have the test done.
  • If you are overweight.
  • If you are pregnant with more than one child such as twins or triplets.
  • If your cervix is incompetent or weak during your pregnancy.
  • If your baby is moving too much in the uterus during the time of testing.
  • If you have taken magnesium sulphate during your pregnancy.
  • If you are at risk of placental abruption as this could cause the placenta to separate from the uterus.
  • If you have placenta previa, where the placenta is situated very low in the uterus.
  • Undergoing the Contraction Stress Test also means that there is the risk that there could be early rupture of your water bag.

Things to Keep in Mind

  • Some doctors prefer the use of oxytocin over a nipple massage as it can cause long and unwanted contractions that may lead to premature labour.


  • If you are experiencing a healthy pregnancy where there is a very low-risk level, the normal routine is for you to be attending your regular prenatal appointments every three to four weeks until you reach your thirty-sixth week of pregnancy. This is the last and final month of your gestation period, and you will now need to be attending more regular doctor’s appointments as the norm is usually one per week until labour.
  • The main aim of the prenatal tests during the ninth month is to keep track of your baby’s condition and to ensure there are no complications that can arise during labour. For example, your doctor will need to keep tabs on your blood pressure to make sure there is no chance of you developing preeclampsia and will need to ensure there is no sugar in your urine, which means that you are suffering from gestational diabetes. She will also need to measure your tummy to see how your baby is growing and check for many other things in order to rule out any complications.
  • It is only if you have abnormal results during all of the other low-risk tests that your doctor will advise you to have the Contraction Stress Test done. This test is very accurate in detecting if there will be a problem due to the fact that it does put pressure on your baby that is similar to what he will have to experience during the actual labour, forcing him to react in the same way he would if you were undergoing a normal delivery. If your baby shows any signs of stress during this procedure, or if your contractions go out of control, the only option left for the doctors, and you will be to deliver the baby as soon as possible.
  • Though babies can be born at thirty-six weeks (though they will be considered premature), it is always better and healthier for your baby to stay in your womb for the entire nine months so that every developmental milestone that your baby needs to reach while in the womb is accomplished.

Always remember that while you may be asked to undergo the stress test and may even get a very unfavourable outcome, these tests are not a hundred per cent accurate and you may still deliver a healthy and happy baby.

Also Read: When and How to Take Pregnancy Tests

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