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Fetal heart monitoring
Alternative namesNon-stress test; NST; CST; Contraction; Scalp monitoring
How the test is performed
EXTERNAL FETAL MONITORING
Sensitive electrodes (monitors) are placed on your abdomen over conducting jelly that can sense both fetal heart rate (FHR) and the strength and duration of uterine contractions. Usually, the output or results of this test are continuous and are printed out, or appear on a computer screen.
This allows your health care provider to monitor if your baby is experiencing fetal distress, and how well the fetus is tolerating the contractions. The decision to move to internal fetal monitoring is based on the information first obtained by external fetal monitoring.
The same monitors described above are placed on your abdomen to measure the ability of the uterus to contract and the FHR. If there is no activity after 30 to 40 minutes, you will be given something to drink or a small meal which may stimulate fetal activity. Other interventions that might encourage fetal movement include the use of fetal acoustic stimulation (sending sounds to the fetus) and gently placing your hands on your abdomen and moving the fetus.
For this test, you will sit with knees and back partially elevated with a cushion under the right hip, which moves your uterus to the left. The same monitors described above are placed on your abdomen to measure uterine contractility and FHR. If contractions are not occurring spontaneously, either a medication (called oxytocin) will be given intravenously, or nipple stimulation will be used to induce contractions.
After being positioned as described above, you will rub the palm of your hand across one nipple through your garments for 2 to 3 minutes. After a 5-minute rest, the nipple stimulation should continue until 40 minutes have elapsed, or 3 contractions have occurred, lasting more than 40 seconds, within a 10-minute period. If a uterine contraction starts, you should stop the nipple stimulation.
This method of monitoring should only be used if your water has already ruptured, you are dilated to a 3 (3 cm), and your baby is positioned properly.
How to prepare for the testAn explanation of the procedure and its risks is provided by your health care provider. You will be asked to wear a hospital gown and sign a consent form prior to the procedure.
How the test will feelExternal fetal monitoring:
Sitting in place for extended periods of time can become uncomfortable for some people. If this is the case, your health care provider (once notified) will help reposition you to a more comfortable position.
The jelly that is placed under the external monitors is the same used for ultrasounds, and may be cold.
Internal fetal monitoring:
Some patients report feeling mild discomfort while the electrode is inserted through the cervix .
Why the test is performedBoth types of tests are performed to evaluate fetal heart rate and variability between beats, especially in relation to uterine contractions. The tests also indicate the frequency and strength of uterine contractions. This information is invaluable in determining how well your baby is tolerating the birth process, and if there needs to be emergency intervention.
Normal ValuesNormal values indicate that the fetus is not in distress by showing a fetal heart rate between 120 to 160 beats per minute, with variability of 5 to 25 beats per minute from the baseline or normal fetal heart rate.
It is not uncommon for the fetal heart rate to drop slightly during a contraction, since placental blood supply is diminished under the compression of a uterine contraction, as long as the FHR recovers quickly once the contraction has stopped.
What abnormal results meanThe following situations or conditions are considered abnormal results, and may be detected by your health care provider (by monitoring the data from these tests):
What the risks areExternal fetal monitoring:
There are no risks associated with external monitoring.
Internal fetal monitoring:
Update Date: 1/27/2002Dominic Marchiano, M.D., Department of Obstetrics & Gynecology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT