Your health care provider will monitor you and your baby throughout your pregnancy. These tests may be done anytime during your pregnancy, especially if you have a high-risk condition, a medical condition, or have had complications with a previous pregnancy. Sometimes a test may be repeated at intervals to show the well-being of the baby over time. Finally, tests may be done if you have reached 41- 42 weeks or are considered postdate, or "overdue."
These tests are designed to miss as few abnormal babies as possible. That means a lot of healthy babies may have abnormal results. It’s important to talk with your health care provider about testing so that you can understand how concerned she is about your baby’s results.
The purpose of the NST is to confirm that the baby is healthy. It is based on the principle that healthy babies move around a lot, and their heart rate increases with movement.
During a non-stress test, you will be hooked up to a fetal monitor just like the one you will have when you're in labor. You will not be given any medication to stimulate or cause movement of the baby or contractions of the uterus – that’s why it’s called a “non-stress test.” Your health care provider doesn’t do anything to stress the baby during the test.
The baby may be moving spontaneously and pass the test without any further stimulation. It may be necessary for you to encourage the baby to move by rubbing your hand over your abdomen, or the clinician may make a loud noise with a special device above the abdomen. When the baby moves, a recording is made of its heart rate.
If the heart rate goes up each time there is movement, the test will likely be considered normal. If the baby doesn't move or the heart rate does not go up when it moves, further testing may be needed to make sure the baby is thriving. A normal NST is described as "reactive" -- the baby moved and the heart rate increased appropriately or "non-reactive" -- the baby did not move or the heart rate did not increase enough when the baby moved. Importantly, many babies with non-reactive NSTs turn out to be healthy after further testing with a contraction stress test or a biophysical profile.
The CST may be done if the non-stress test is abnormal. The purpose is to predict how well the baby will do during labor, which is a stressful process not just for you, but the baby as well. Every contraction momentarily deprives the baby of its usual blood and oxygen supply. For most babies this is not a problem, but some babies have a hard time. A CST shows whether the baby has an abnormal heart rate pattern during contraction stress.
Again, a fetal monitor is used. Contractions may be induced in a variety of ways. Breast stimulation causes the release of oxytocin, the hormone that causes contractions. To cause contractions, you will be given an infusion of oxytocin or Pitocin. The resulting contractions are similar to those you will have during labor. If the baby's heart rate slows down rather than speed up after a contraction, the baby may be having a problem and may have more serious problems during labor.
Most women describe the test as slightly uncomfortable but not painful.
If the test is abnormal, you may be admitted into the hospital. If there is a problem with the baby, your doctor may want to deliver the baby early, by cesarean section.
A biophysical profile is a combination of a non-stress test and detailed ultrasound scanning. If the non-stress test is not reactive, then a biophysical profile may be done. The profile looks at fetal movement, fetal body tone, fetal breathing efforts, amniotic fluid volume, as well as the result of the non-stress test.
Each component is given a score of "2" if the result is normal, and "0" if the test is abnormal. A score of 8-10 out of 10 is normal. A score of 6 is unclear and you may be required to repeat the test within 12-24 hours. A score of 0-4 is abnormal and often means the baby might be better off outside the uterus, and a cesarean section may be recommended.
In some cases, a modified biophysical profile is done. This combines the non-stress test with an ultrasound that just looks at the amniotic fluid volume. If both of these tests are normal, some doctors believe that this is as reassuring as the full biophysical profile. Furthermore, it is less time consuming. Your health care provider will recommend the tests that are best for you and your baby.
If you are having a healthy pregnancy, these tests may never be done. If you are at high-risk or have gone a week or so past your due date, your health care provider may decide that some of these tests are needed.
© 2011 University of Maryland Medical Center (UMMC). All rights reserved.
UMMC is a member of the University of Maryland Medical System,
22 S. Greene Street, Baltimore, MD 21201. TDD: 1-800-735-2258 or 1.866.408.6885