Home > Encyclopedia of Nursing & Allied Health > Electronic Fetal Monitoring

Definition

The electronic fetal monitor (EFM) is a device that records an unborn baby's heart rate and the presence or absence of the mother's uterine contractions.

Purpose

The EFM is used to assess fetal well being during routine prenatal visits. It is also used during labor and delivery when high-risk factors exist or when a clinical condition develops beforehand that places the fetus at risk. High risk factors for EFM during labor include:

• low gestational age
• high maternal age
• placenta or cord problems
• meconium in the aminotic fluid
• hypertension
• proteinuria
• facial nerve palsy

A fetus having trouble in labor often exhibits characteristic changes in heart rate after a contraction (late decelerations). Trouble is also indicated by significant slowing of the heart rate during a contraction (variable deceleration). If the fetus is not receiving enough oxygen to withstand the stress of labor, and delivery is many hours away, a cesarean section (C-section) may be necessary.

Description

The monitor produces a continuous paper record of the fetal heart rate (FHR) and records uterine contractions. FHR is captured on the top part of the paper printout; uterine activity, when monitored, appears on the lower part of the tracing.

Electronic fetal monitoring can be performed externally or internally. The external ultrasound approach is non-invasive and uses sensors (electrodes) placed on the mother's abdomen with an elastic belt. Another belt holds the contraction monitor.

External electronic fetal monitoring includes a non-stress test, which measures FHR accelerations with normal movement of the fetus. Sometimes the fetal movement is encouraged by giving the mother a small meal or something to drink. Fetal acoustic stimulation and moving the fetus by rubbing the abdomen gently may also be used.

Two contraction stress tests, which measure the placenta's ability to provide enough oxygen to the fetus during pressure, are also used with electronic fetal monitoring. The nipple stimulation contractions stress test involves the mother self-stimulating her nipple while contractions and FHR are monitored. Another test, called oxytocin stimulation, involves the administration of the hormone oxytocin intravenously until three uterine contractions are observed within ten minutes, during which time the FHR is monitored.

Sometimes, it is difficult to hear the baby's heartbeat with the monitoring device. Other times, the monitor may show subtle signs of a developing problem. In either case, the physician may recommend the use of an internal monitor, which provides a more accurate record of the baby's heart rate. The internal monitor (or fetal scalp electrode) uses an electrode attached to the baby's scalp through the cervix during an internal vaginal exam. The internal monitor can only be used when the cervix is dilated.

In 1995, a technical bulletin issued by the American College of Obstetricians and Gynecologists (ACOG) reported that the prudent use of intermittent auscultation (listening) of fetal heart rate is equivalent to continuous electronic fetal monitoring in a low-risk pregnancy. Intermittent auscultation involves listening to the FHR every 15 minutes during active labor until complete cervical dilation. From complete dilation to delivery, the FHR should be obtained every five minutes and timed to obtain the FHR during a contractions and for 30 seconds afterwards. In complicated pregnancies, however, continuous EFM is recommended during labor. EFM is used in most deliveries directed by physicians.

Preparation

There are no special preparations required for external fetal monitoring. Preparation for placement of an internal scalp lead (ISL) is the same as for a routine vaginal exam.

Complications

In general, no risks are associated with external fetal monitoring. However, the test can initiate labor and is generally not given to mothers at risk for preterm labor or with a condition that requires a cesarean section. Internal monitoring poses risks associated with improper placement of the electrodes.

Some data indicate that EFM leads to unnecessary C-sections. Another drawback includes loss of maternal mobility when used during labor, which may slow labor.

Results

The normal fetal heart rate (FHR) ranges from 120 to 160 beats per minute (bpm). Just as an adult's heart rate rises with movement, FHR rises when the baby moves. A reactive heart rate tracing (also known as a reactive non-stress test, or NST) is considered a positive sign of fetal well being. A non-reactive NST may or may not imply fetal well being. The monitor strip is considered to be reactive when the FHR rises at least 15 to 20 bpm above the baseline heart rate for at least 20 seconds. This must occur at least twice in a 20-minute period.

Results are considered abnormal if the FHR drops below 120 or rises above 160 for sustained periods. In either of these cases the baby may be exhibiting fetal distress. A mean FHR of less than 110 bpm may indicate bradycardia (slow heart beat). A mean FHR of over 160 bpm may indicate a tachycardia (rapid beating of the heart). However, some babies who are having problems may not exhibit such clear signs.

During a contraction, the flow of oxygen from the mother through the placenta to the baby is temporarily stopped. It is as if the baby has to hold its breath during each contraction. Both the placenta and the baby are designed to withstand this condition. Between contractions, the baby should be receiving more than enough oxygen to do well during the contraction.

One sign that a baby is not getting enough oxygen between contractions is a drop in the baby's heart rate after the contraction (late deceleration). The heart rate recovers to a normal level between contractions, only to drop again after the next contraction. This is a more subtle sign of distress. Trouble is also indicated by significant slowing during a contraction (variable decelerations).

Fetal monitoring is not a perfect test. Fetal assessment in labor is subject to differences in interpretation and consequent intervention; therefore, institutional policies and procedures should be followed.

Health care team roles

Electronic fetal monitoring is primarily conducted by specialists in obstetrics and gynecology. Qualified registered nurses and advanced practice nurses may assist in or conduct electronic fetal monitoring.

Training

Applying the external monitor is simple, but requires practice in the proper placement of the monitoring devices. The interpretation of the tracings, however, requires continued vigilance in education and clinical practice. Training should include instruction in auscultation, electronic FHR monitoring, and evaluation of uterine activity.

---

KEY TERMS

---

Auscultation—Listening to sounds within organs to help in diagnosis in treatment.

C-section—A cesarean section; delivery of a baby through an incision in the mother's abdomen instead of through the vagina.

Late deceleration—Transient fetal brachycardia exceeding 100 beats per minute which reaches its height more than 30 seconds after the peak of the uterine contraction.

Non-stress test—A record of the fetal heart rate in the absence of contractions (stress).

Reactive stress test—A positive sign of fetal well being. The FHR rises at least 20 beats per minute above the baseline heart rate for at least 20 seconds, occurring at least twice in a 20-minute period.

Variable deceleration—Fetal bradycardia below 100 beats per minute denoting compression of the umbilical cord at the height of a uterine contraction.

---

Maggie Boleyn, R.N., B.S.N.