Norm of External Fetal Monitoring, Non–Stress Testing (NST)
Fetal heart rate (FHR) and variability normal.
Usage of External Fetal Monitoring, Non–Stress Testing (NST)
Monitoring FHR and uterine patterns under normal, nonstressful circumstances during late pregnancy (third trimester). This test is able to detect FHR accelerations as associated with fetal movement. In the presence of uterine contractions, decelerations may be observed.
Description of External Fetal Monitoring, Non–Stress Testing (NST)
A noninvasive test in which an electronic transducer is placed on the pregnant abdomen to amplify the FHR while a cardiotachometer records FHR and a pressure sensor (tocodynamometer) records any uterine contractions. A baseline FHR is determined, fetal movements are recorded, and any change in FHR associated with movement is evaluated.
Interpretation of External Fetal Monitoring, Non–Stress Testing (NST)
|Reactive = At least 2 accelerations during 20 minutes.|
|Nonreactive = None of the reactive criteria met; long-term variability minimal.|
|Unsatisfactory = Unable to obtain adequate tracing; fetal patterns are borderline for criteria. Reschedule testing as indicated by condition.|
Professional Considerations of External Fetal Monitoring, Non–Stress Testing (NST)
Consent form NOT required. Client agreement is recommended.
- Obtain a fetal heart monitor and an electroconductive gel.
- Cleanse the transducer, tocodynamometer, and monitor connections with alcohol pads.
- The client is instructed to empty her bladder and then is placed in a left lateral or semi-Fowler's position (with left hip roll) with the abdomen exposed. Use Leopold's maneuvers to determine fetal outline. Palpate fetal spine and locate occiput. The most distinct fetal heart tones are obtained over area of the fetal shoulders (usually lower left or lower right quadrant).
- The transducer is coated with electroconductive gel and strapped over the location of fetal heart tone.
- The alarm limits for FHR are set, and a baseline heart rate over a 2-minute period is determined.
- Assess uterine fundus to locate area where contractions are best palpated and not affected by fetal position. Strap tocodynamometer over this area.
- Client is monitored for a minimum of 30 minutes. During this time, monitor will electronically record any fetal movements, including kicking. If monitor does not have this capacity, client will be asked to press a button each time a movement is felt in order to record activity.
- Fetus should exhibit accelerations during a 20-minute period. Acceleration is defined as an increase of 15 bpm over fetal baseline rate, lasting 15 seconds.
- Weekly external fetal monitoring is indicated for diabetes, hypertension, fetal growth retardation, and pregnancy >42 weeks of gestation.
- In the event of a nonreactive result, client will be scheduled for a contraction stress test (CST)/oxytocin challenge test (OCT).
Client and Family Teaching
- For antepartal testing, the client should eat a full meal just before the test.
- The test poses no risk or harm to the client or the fetus.
Factors That Affect Results
- False-positive result associated with inadequate testing time, maternal hypotension, and maternal medications.
- False-negative result associated with improper placement of monitoring devices.