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External Fetal Monitoring
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External Fetal Monitoring

In this noninvasive test, an electronic transducer and a cardiotachometer amplify and record fetal heart rate (FHR) while a pressure-sensitive transducer (tocodynamometer) records uterine contractions. Fetal monitoring records the baseline FHR (average FHR over two contraction cycles or 10 minutes), periodic fluctuations in the baseline FHR, and beat-to-beat heart rate variability. External fetal monitoring is also used during other tests of fetal health, notably the nonstress test and the contraction stress test (CST).


  • To measure FHR and the frequency of uterine contractions
  • To evaluate antepartum and intrapartum fetal health during stress and non-stress situations.
  • To detect fetal distress
  • To determine the necessity for internal fetal monitoring
  • To assess uterofetoplacental physiology and adequacy of fetal oxygenation.

Patient preparation

  • Explain to the patient that this test assesses fetal health.
  • Describe the procedure and answer all questions. Assure her that external fetal monitoring is painless and won't hurt the fetus or interfere with normal labor.
  • Explain that she may have to restrict movement during baseline readings but that she may change position between the readings.
  • Make sure the patient or a responsible family member has signed an informed consent form.


Monitor, transducer, paper, ultrasound transmission jelly; elastic band, stockinette, or abdominal strap.

Procedure and posttest care

  • Place the patient in the semi-Fowler or left lateral position, with her abdomen exposed. Cover the ultrasound transducer receiver crystal with ultrasound transmission jelly.
  • Palpate the patient's abdomen to identify the fetal chest area, locate the most distinct fetal heart sounds, and then secure the ultrasound transducer over this area with the elastic band, stockinette, or abdominal strap.
  • Check the recording equipment for calibration, adequate paper, and alarm boundaries.
  • During monitoring, check the elastic band, stockinette, or abdominal strap to ensure that the fit is comfortable yet tight enough to produce a good tracing.
  • As labor progresses, reposition the pressure transducer as necessary so that it remains on the fundal portion of the uterus. You may have to reposition the ultrasound transducer as fetal or maternal position changes.
  • Repeat antepartum monitoring weekly as long as indications, such as pregnancy over 42 weeks' gestation or any other high-risk pregnancy or fetal growth retardation, persist.
  • If FHR patterns indicate distress, fetal oxygenation can often be improved by turning the mother on her side (preferably left) to alleviate supine hypoxia, administering oxygen to the mother, or loading maternal fluids to increase placental perfusion. If the FHR returns to normal, labor may continue. If abnormal FHR patterns persist, cesarean birth may be required.

Antepartum monitoring with nonstress tests

  • Tell the patient to hold the pressure transducer in her hand and to push it each time she feels the fetus move. Some monitoring systems document fetal movement without input from the mother.
  • Monitor baseline FHR until you record two fetal movements that last longer than 15 seconds each and cause heart rate accelerations of more than 15 beats/minute from the baseline. If you can't obtain two FHR accelerations within 20 to 30 minutes, shake the patient's abdomen to stimulate the fetus, and repeat the test.

Antepartum monitoring with CST

  • Induce contractions by oxytocin infusion or nipple stimulation (endogenous oxytocin).
  • When administering oxytocin, infuse a dilute solution at a rate of 0.5 to 1.0 mU/minute, increasing the oxytocin rate until the patient experiences the desired contraction pattern.
  • When using nipple stimulation, tell the patient to stimulate one nipple by hand until contractions begin. Some doctors recommend using a water­soluble jelly to prevent nipple damage. If a second contraction doesn't occur in 2 minutes, have her stimulate the nipple again. Stimulate both nipples if Contractions don't occur in 15 minutes. Continue until the desired contraction pattern occurs.
  • If no decelerations occur during three contractions, the patient may be discharged. Late decelerations during any of the contractions require notification of the doctor and further tests.

Intrapartum monitoring

  • Secure the pressure transducer with an elastic band, a stockinette, or an abdominal strap over the area of greatest uterine electrical activity during contractions (usually the fundus).
  • Adjust the machine to record 0 to 10 mm Hg pressure between palpable contractions.
  • Reposition the ultrasound and pressure transducers as necessary to ensure continuous accurate readings. Review the tracings frequently for baseline abnormalities, periodic changes, variability of changes, and uterine contraction abnormalities.
  • Record maternal movement, administration of drugs, and procedures performed directly on the tracing to assist evaluation of changes in the tracing.
  • Report abnormalities immediately.

During CST, watch for fetal distress with oxytocin infusion or nipple stimulation.

Normal findings

Normal baseline FHR ranges from 120 to 160 beats/minute, with a variability of 5 to 25 beats/minute. For the antepartum nonstress test, the fetus is considered healthy and should remain so for another week if two fetal movements causing a heart rate acceleration of more than 15 beats/minute from baseline FHR occur in a 20-minute period.

For the CST, the fetus is assumed to be healthy and should remain so for another week if three contractions occur during a 10-minute period, with no late decelerations.

Abnormal findings

Bradycardia (FHR < 120 beats/ minute) may indicate fetal heart block, malposition, or hypoxia. Fetal bradycardia may also be drug-induced. Tachycardia (FHR > 160 beats/ minute) may result from maternal fever, tachycardia, hyperthyroidism, or use of vagolytic drugs or narcotics; early fetal hypoxia; or fetal infection or arrhythmia.

Decreased variability (a fluctuation of < 5 beats/minute in the FHR) may be caused by fetal arrhythmia or heart block; fetal hypoxia, central nervous system malformation, or infections; or vagolytic drugs. FHR accelerations may result from early hypoxia. They may precede or follow variable decelerations and may indicate that the fetus is in a breech position.

For the antepartum nonstress test, a positive result (< two accelerations of FHR that last longer than 15 seconds each, with a heart rate acceleration over 15 beats/minute) indicates an increased risk of perinatal morbidity and mortality and usually requires CST.

For the CST, persistent late decelerations during two or more contractions may indicate increased risk of fetal morbidity or mortality. Hyperstimulation (long or frequent uterine contractions) or suspicious results require biophysical profile assessment. If findings are unsatisfactory, cesarean birth may be indicated.

Interfering factors
  • Gestational age
  • Drugs that affect the sympathetic and parasympathetic nervous systems (possible low FHR)
  • Certain fetal positions
  • Excessive maternal or fetal activity (possible difficulty in recording uterine contractions or FHR)
  • Maternal obesity (possible difficulty due to density of abdominal wall)
  • Loose or dirty leads or transducer connections (possible production of artifacts )

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