Monitoring the Baby’s Heart Rate.
Why is the baby’s heart rate monitored? The pattern of the baby’s heartbeat during labor is often a good indicator of the baby’s well-being. The normal fetal heart rate (FHR) is 120 to 160 beats per minute. A normal heart rate suggests that the baby is receiving enough oxygen from the mother’s bloodstream. The typical pattern is for the baby’s heart rate to slow somewhat during a contraction, and rise again when the contraction ends.
Abnormal variations in heart rate can indicate decreased oxygen in the blood and tissues of the fetus, which can lead to potential damage to the baby. Patterns that can cause concern: Abnormally fast or slow heartbeat, a heart rate pattern that takes a long time to return to normal after a contraction (prolonged deceleration), one that slows late in the contraction and stays slow (late deceleration), or one that doesn’t respond to contractions (no variability). These patterns may lead to more monitoring, further testing, or interventions.
Please note: heart rates are normally quite variable, and interpretation of monitoring is quite complex; parents should not attempt to evaluate their own monitoring results.
How is the baby’s heart rate monitored? It can be monitored either intermittently, by auscultation (a caregiver listens to the heart beat, using a fetoscope or a Doppler device, and then charts the results) or intermittently by electronic fetal monitoring (EFM), or continuous EFM, which produces a printed record of heart rate and contractions for nurses to review.
There is controversy regarding electronic monitoring with high-risk situations, such as premature labor, placenta or cord problems, or a complicating disease like diabetes, hypertension, or sickle cell anemia. There is little evidence* that EFM is beneficial compared to frequent auscultation. In multiple studies of the issue, the only significant benefit of EFM was a reduction in seizures sometimes seen in the first month after birth (seen in .5% of newborns). The reduction in seizures was generally seen with women who had prolonged labors, or those that were induced or augmented with pitocin. Therefore, EFM is usually recommended with pitocin, where it also is helpful in monitoring the strength of contractions to screen for uterine hyper-stimulation.
The caregiver or nurse checks fetal heartbeats and variability before, during, and after contractions, either using a fetal stethoscope to listen to the heart, or a Doppler ultrasound stethoscope, a small hand-held device which uses sound waves to monitor the heart beat. In low risk births, ACOG suggests monitoring at least ever 30 minutes during active labor, and at least every 15 minutes during second stage labor. When risk factors are present, it should be evaluated every 15 minutes, and every 5 minutes in second stage labor.
Nurses may also palpate (feel) the mother’s abdomen to check for strength of contractions.
Availability: Most medical care providers are more familiar with and more comfortable with using EFM; they may not even be effectively trained in auscultation or interpretation of results. This method also requires more staff time and attention than EFM, and may not be possible in hospitals without adequate nursing staff.
Electronic Fetal Monitoring: External.
What is it? The mother has two straps placed around her abdomen, which hold: an ultrasound device which monitors the baby’s heart rate, and a tocometer, which monitors the strength, duration, and frequency of contractions. They are connected to video screens (at the bedside, and/or at the nurse’s station) and a printer which produces graphs of the fetal heart rate and the intensity of the contractions. The record should be checked every 15-30 minutes in active labor, every five minutes in second stage.
When is it used? Typically, upon arrival at the hospital, a laboring mother will have the monitor placed on her for 20 minutes to establish a “baseline”, a sense of her baby’s normal heart rate and reaction to contractions. If the patient requests it, and if the baseline meets staff expectations for a positive situation, the monitor can then be removed. It will again be used for intermittent monitoring, or for continuous monitoring if interventions such as pitocin or epidural or used, or if the caregiver has concerns about the baby. Some hospitals routinely place the monitor upon admission, and leave it on throughout the entire labor.
In 1999, EFM was used in
73% of births in
How does it affect labor? The mother is typically confined to her bed while being monitored. Some hospitals have telemetry units which allow her to walk around the hospital with the monitor; some hospitals have waterproof telemetry, which allows her to bathe or shower. Because readings are most accurate when she is immobile, generally it’s recommend that she remain inactive. If she changes position, a nurse may have to readjust the monitor. (Lying on side can minimize risk of supine hypertension.)
Also, some comfort techniques such as back massage, and effleurage (light stroking) of the belly, may be awkward or impossible to do with the monitor straps in place.
Criticisms of EFM: Varying definitions of “problematic” results: There is no clear consensus on what heart patterns are normal variations during labor, and which are clear signs of danger to the fetus. Interpretation can be very subjective. In studies of interpretations of results and subsequent care recommendations, there were significant differences between care providers who were extensively trained in interpretation. Amongst the average caregiver in a hospital setting, interpretations may be even less clear-cut.
Over-diagnosis of fetal distress: Caregivers tend to “err on the side of caution”. Bean (1990) estimates that the ‘false positive’ rate for fetal distress diagnosis is as high as 40%. Van der Berg et al found that 71-95% of babies diagnosed as distressed during labor did not have that diagnosis confirmed at birth.
What are the advantages of EFM?
For baby: If the fetal heart rate slows down, stops, or is slow to recover from contractions, it is immediately apparent. Can detect reduced oxygen flow caused by cord compression (more common after membranes rupture spontaneously or are ruptured), by Pitocin augmented contractions, or by narcotic and epidural related changes in maternal blood pressure.
For parents: Some parents find a monitor reassuring, and like to listen to baby’s heart beat.
For caregivers: Multiple patients can be monitored from nurses’ station. Permits use of larger amounts of Pitocin than would be ‘safe’ without continuous monitoring, both of heart rate and contractions. Provides more information to be evaluated. Printout provides a legal record to justify the basis for decisions to intervene. Monitoring units are expensive, and would not be cost-effective if used only in high-risk labors.
What are the disadvantages of EFM?
For baby: The mother’s immobility, and likelihood to remain on her back or semi-sitting, may decrease oxygen flow to the baby, creating the very problems EFM is monitoring for.
For parents: Unable to move around and limited choices of positions to ease labor pain and help labor progress. The noise from the monitor can be disturbing, though usually volume can be adjusted. De-humanizing: Some mothers report that after the monitor is placed, caregivers and support people pay more attention to the readouts than to the mother herself. Lack of understanding of normal variations in heart beat can cause unwarranted anxiety in parents attempting to evaluate the results.
Most significant risk is unnecessary c-sections, due to potential for over-diagnosis of fetal distress in a healthy baby. There is a 1.3 to 2.7-fold increased likelihood of cesarean section with continuous EFM. The likelihood of c-section due to fetal distress diagnosis specifically is 2.0 – 4.1-fold increase. The chance of operative delivery (including c-section, vacuum extractor, and forceps) is increased by about 30% with EFM.
For caregivers: Few disadvantages. Many caregivers prefer EFM for the reasons above.
Electronic Fetal Monitoring: Internal
What is it? After the mother is 2 cm dilated, an internal monitor can be placed. Wires are inserted into the cervix, and a spiral electrode is placed under the skin of baby’s scalp or other presenting part. Membranes must be ruptured to place electrode. The electrode measures baby’s heart rate. Often, an internal uterine pressure catheter is also placed to more accurately measure the strength of contractions.
When is it used? In some high risk births, or if the external monitor shows suspicious results, caregiver may use internal monitor to get more accurate information.
How does it affect laboring woman? Can’t walk or stand. Can turn over.
Advantages: Similar to external monitor, but internal offers increased accuracy of readings.
Disadvantages: Similar to external monitor, plus risk of infection from AROM, fetal infection from implantation of the electrode.
What if monitoring results show a non-ideal heartbeat pattern?
Some sources recommend fetal scalp sampling (a procedure which takes a blood sample from the baby’s scalp to help confirm fetal oxygen levels) to determine whether a diagnosis of fetal distress is warranted, and whether interventions are necessary.
“External Electronic Fetal Monitor.” From Birth as an American Rite of
Passage by Robbie Davis Floyd. http://www.birthpsychology.com/messages/efm/efm.html
“Intrapartum Electronic Fetal
Monitoring” by U.S. Preventive Services Task Force.
Abstracts for seventeen journal articles: http://www.changesurfer.com/Hlth/EFM.html