Electronic fetal monitoring
Electronic Fetal Monitoring
Electronic fetal monitoring (EFM) involves the use of an electronic fetal heart rate (FHR) monitor to record the baby's heart rate. Elastic belts are used to hold sensors against the pregnant woman's abdomen. The sensors are connected to the monitor and detect the baby's heart rate as well as the uterine contractions. The monitor then records the FHR and the contractions as a pattern on a strip of paper. Electronic fetal monitoring is performed late in pregnancy or continuously during labor to ensure normal delivery of a healthy baby. EFM can be utilized either externally or internally in the womb.
All electronic fetal monitors detect the FHR and maternal uterine activity (UA), and both are displayed for interpretation since the pattern of the baby's heartbeat during labor often reflects the baby's condition. During contractions, the normal pattern is for the FHR to slow somewhat, picking up again as the contraction ends. The EFM continuously prints out a record of both the FHR and the duration and frequency of the uterine contractions, so that deviations from normal patterns can be identified. Certain variations in this pattern, such as precipitous drops in the FHR at the end of a contraction can constitute a true life or death situation requiring emergency delivery of the baby. Prior to the use of EFMs, nurses and doctors periodically monitored the baby's heartbeat manually by placing a stethoscope on the mother's abdomen. It is important to note that the EFM is a screening tool and not diagnostic of any particular disorder.
Fetal asphyxia (an impaired exchange of oxygen and carbon dioxide) is recognized as an important cause of stillbirth and neonatal death. Asphyxia has also been implicated as a cause of cerebral palsy , although many cases of cerebral palsy have occurred without evidence of birth asphyxia. Most fetuses, however, tolerate intrauterine hypoxia during labor and are delivered without complications. If the interruption to the supply of oxygen is short, the baby may recover without any damage. If the time is longer, there may be some injury that is reversible. If the time period without oxygen is especially long, there may be permanent injury to one or more organs of the body.
Fetal monitoring can be helpful in a variety of different situations. During pregnancy, fetal monitoring can be used as a part of antepartum testing . If the practitioner feels that a baby may be at risk for problems during pregnancy, non-stress tests, biophysical profiles, or even contraction stress tests are performed twice a week to monitor fetal well-being. In this test, changes in the baby's heart rate are noted with the fetus's own movements. The heart rate of a healthy baby should go up whenever she or he moves.
Using the external fetal monitor is simple and painless. Two belts are placed around the pregnant woman's abdomen. One is to hold the transducer that picks up the FHR and the other is to hold a tocodynanometer, which picks up uterine activity or contractions. External monitoring of the fetus is accomplished by means of a transducer that emits continuous sound waves (ultrasound). A water-soluble gel is placed on the underside of the transducer to permit the conduction of fetal heart sounds. When the transducer is placed correctly on the maternal abdomen, the sound waves bounce off the fetal heart and are picked up by the electronic monitor. The actual moment-by-moment FHR can be simultaneously viewed on a screen while being printed on graph paper. Incorrect placement of the transducer may detect a pulsating maternal vessel with a resultant swooshing sound (uterine soufflé), and the rate will be the same as the maternal pulse. Maternal uterine activity is noted and recorded when the pressure of a contraction pushes on a sensor, which is on the underside of a tocodynanometer. Once again, incorrect placement may not completely detect contractions. The sensor on the tocodynanometer must be placed on that part of the uterus that can be palpated easily. If it is too high or too low, the contractions may not be detected.
If it becomes difficult to detect the FHR with the external monitor or if there are subtle signs of a developing problem, the practitioner may recommend the use of an internal monitor. The measurement of fetal heart activity is performed most accurately by attaching an electrode directly to the fetal scalp. This is an invasive procedure that requires the rupture of membranes (amniotomy) and is associated with occasional complications.
An internal monitor may also be used to determine the actual strength of the contraction as well as the resting tone of the uterus. A woman may appear to be having strong contractions but not be progressing in labor. Progress in labor is determined by cervical dilation. The insertion of an intrauterine pressure catheter (IUPC) permits the determination of the strength of the contractions in millimeters of Hg, a measurement used for pressure. A good labor pattern that facilitates cervical dilation can be calculated by taking the difference in pressure between the peak of the contraction and the resting tone and adding them up over a ten-minute period. The unit of measurement for this calculation is called a Montevideo unit, and ideally the sum total of the pressures should be between 150 and 250 Montevideo units to achieve cervical dilation. If the calculation is in this range and the woman's cervix is not changing, then and only then can a diagnosis of failure to progress be made. The IUPC also provides an accurate measurement of the resting tone of the uterus. It is important that the uterus relax between contractions in order for the baby to receive oxygen. If the uterus is not relaxing or if the resting tone is rising, this can be an indication of a placental abruption (the tearing away of the placenta from the wall of the uterus).
Another use of an IUPC is for amnioinfusion. This is a procedure in which a physiologic solution (such as normal saline) is infused into the uterine cavity to replace the amniotic fluid. It is used to relieve cord compression, reduce fetal distress caused by meconium staining, and as a correction of decreased amniotic fluid.
There are no special preparations needed for fetal monitoring. An explanation of the procedure and its risks should be provided by the healthcare provider and a consent form may be signed for the procedure.
Besides the risk of an unnecessary cesarean section , other risks posed to the mother by EFM include her immobilization in bed. Immobilization simultaneously limits changing positions for comfort and causes changes in blood circulation, which decreases the oxygen supply to the fetus and can lead to abnormal changes in the FHR on the EFM that was applied to detect these changes. Another problem with the use of the EFM is that practitioners have a tendency to focus on it instead of the laboring woman. For these and other reasons, the United States Preventive Services Task Force states that there is some evidence that using EFM on low-risk women in labor might not be indicated. EFM, however, has become an accepted standard of care in many settings in the United States for management of labor. Interestingly, there has not been a reported reduction in perinatal morbidity in the United States with the use of EFM. There is a benefit to using EFM in women with complicated labors, such as those induced or augmented with oxytocin, prolonged labors, vaginal birth after having a cesarean section, abnormal presentation, and twin pregnancy.
Generally the insertion of a fetal scalp electrode is a safe procedure, but it may occasionally cause umbilical cord prolapse or infection due to early amniotomy. Problems could also occur if the electrode or IUPC causes trauma to the eye, fetal vessels, umbilical cord, or placenta. Scalp infections with the herpes virus or group B streptococcus are possible, and concern has been raised regarding the potential for enhancing transmission of the human immunodeficiency virus (HIV). As with any procedure, the potential benefit of EFM must be weighed against the potential risks.
The average fetal heart rate is in the range of 110 to 160 beats per minute (bpm). A baby who is receiving sufficient oxygen through the placenta moves around and the monitor strip will show the baby's heart rate rising briefly as he or she moves. The monitor strip is considered to be reactive when the baby's heart rate elevates at least 15 bpm above the baseline heart rate for at least 15 seconds twice in a 20-minute period. Other indicators of fetal well-being include short term variability (STV), which constitutes changes in the FHR from one beat to another, and long term variability (LTV), which is changes in the FHR over a long period of time.
Amnioinfusion —A procedure whereby a physiologic solution such as normal saline or lactated ringer's solution is infused through a lumen in an intrauterine pressure catheter into the uterus to alleviate cord compression and to help dilute meconium staining.
Amniotic fluid —The liquid in the amniotic sac that cushions the fetus and regulates temperature in the placental environment. Amniotic fluid also contains fetal cells.
Amniotomy —Rupturing or breaking the amniotic sac (bag of waters) to permit the release of fluid.
Asphyxia —Lack of oxygen.
Deceleration —A decrease in the fetal heart rate that can indicate inadequate blood flow through the placenta.
Hypoxia —A condition characterized by insufficient oxygen in the cells of the body
Meconium —A greenish fecal material that forms the first bowel movement of an infant.
Perinatal —Referring to the period of time surrounding an infant's birth, from the last two months of pregnancy through the first 28 days of life.
If the baby's heart rate drops very low or rises very high, this can signal a serious problem if it occurs for longer than a ten-minute period. During a contraction, the flow of oxygen (from the mother) through the placenta (to the baby) is temporarily blocked. The baby should be capable of withstanding this condition since it is receiving sufficient oxygen between contractions. The first sign that a baby is not getting enough oxygen between contractions is often a drop in the baby's heart rate after a contraction, called a late deceleration. The baby's 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. These babies will do fine if they are delivered in a short period of time following the onset of the late decelerations. Sometimes, these signs develop long before delivery is expected. In that case, a c-section may be necessary.
One of the worst indications of fetal distress, however, is a tracing that shows no variability at all. It is a flat tracing and indicates that the baby has sustained a severe assault on its central nervous system. It is not capable of responding to stimuli in its environment. The mother may report that she has experienced decreased fetal movement as the baby has only enough oxygen to keep the heart beating. It is for this reason that all pregnant women should be taught to keep track of fetal movement every day and to report any significant changes.
See also Apgar testing; Cesarean section.
Freeman, Roger, et al. Fetal Heart Rate Monitoring, 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2003.
Gabbe, Steven. Obstetrics: Text and Pocket Companion Package. St. Louis, MO: Harcourt Health Sciences Group, 2003.
Tucker, Susan. Pocket Guide to Fetal Monitoring and Assessment, 4th ed. St. Louis, MO: Mosby, 2000.
American College of Obstetricians and Gynecologists. 409 12th Street, SW, PO Box 96920, Washington, DC 20090. Web site: <www.acog.org>.
Association of Women's Health, Obstetric, and Neonatal Nursing. 2000 L Street, NW, Suite 740, Washington, DC 20036. Web site: <www.awhonn.org>.
International Childbirth Education Association Inc. (ICEA). PO Box 20048, Minneapolis, MN 55420. Web site: <www.icea.org>.
Linda K. Bennington, BSN, MSN, CNS
Electronic Fetal Monitoring
Electronic Fetal Monitoring
Electronic fetal monitoring (EFM) is a method for examining the condition of a baby in the uterus by noting any unusual changes in its heart rate. Electronic fetal monitoring is performed late in pregnancy or continuously during labor to ensure normal delivery of a healthy baby. EFM can be utilized either externally or internally in the womb.
The heart rate of a fetus undergoes constant adjustment as it responds to its environment and other stimuli. The fetal monitor records an unborn baby's heart rate and graphs it on a piece of paper. Electronic fetal monitoring is usually advised for high-risk pregnancies, when the baby is in danger of distress. Specific reasons for EFM include: babies in a breech position, premature labor, and induced labor, among others.
When electronic fetal monitoring was originally introduced in the 1960s and 1970s, the hope was that it would help physicians diagnose fetal hypoxia, or lack of oxygen, in time to prevent damage to the baby. This lack of oxygen, also known as perinatal asphyxia or birth asphyxia, is an important cause of stillbirth and newborn deaths. It occurs when there are less than normal amounts of oxygen delivered to the body or an organ and there is build-up of carbon dioxide in the body or tissue. A lack of blood flow to an organ can cause asphyxia. Perinatal asphyxia can occur a long time before birth, shortly before birth, during delivery, or after birth. If the interruption to the supply of oxygen is short, the baby may recover without any damage. If the time is longer, there may be some injury that is reversible. If the time period without oxygen is very long, there may be permanent injury to one or more organs of the body. It is important to detect any signs of asphyxia as soon as possible. One of the signs is an abnormal heart rate and rhythm in the unborn baby, which can be detected by electronic fetal monitoring.
The fetal monitor is a more intricate version of the machine that a health care provider uses to listen to a baby's heartbeat. The monitor that is used during prenatal visits just picks up the sound of the baby's heart beating. The fetal monitor also keeps a continuous paper record of the heart rate. In addition, the fetal monitor can record uterine contractions on the lower part of the paper strip. This helps the doctor or midwife determine how a baby is handling the stress of contractions. The normal pattern is for the baby's heartbeat to drop slightly during a contraction and then go back to normal after the contraction is over. EFM looks for any changes from this normal pattern, particularly if there is a drastic drop in the baby's heart beat or if the heart rate does not recover immediately after a contraction.
Because it is an indirect test, it is not perfect. When an adult complains to a provider about not feeling well, checking the heart rate is only one of many things that the doctor will do. With an unborn baby, however, checking the heart rate is basically the only thing that a doctor or midwife can do.
Fetal monitoring can be helpful in a variety of different situations. During pregnancy, fetal monitoring can be used as a part of antepartum testing. If the practitioner feels that a baby may be at increased risk of problems toward the end of pregnancy, a baby can be checked every week or every other week with a non-stress test. In this test, changes in the baby's heart rate are measured along with the fetus' own movements. The heart rate of a healthy baby should go up whenever she or he moves.
Fetal monitoring is used on and off during early labor. As labor progresses, more monitoring is often needed. Usually, as the time for delivery nears, the monitor is left on continuously since the end of labor tends to be the most stressful time for the baby.
A baby who is having trouble in labor will show characteristic changes in heart rate after a contraction (late decelerations). If a baby 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.
Using the external fetal monitor is simple and painless. Two elastic belts are placed around the mother's abdomen. One belt holds a listening device in place while the other belt holds the contraction monitor. The nurse or midwife adjusts the belts to get the best readings from each device.
Sometimes, it is difficult to hear the baby's heartbeat with the external monitoring device. Other times, the monitor may show subtle signs of a developing problem. In either case, the doctor or midwife may recommend that the external belt be replaced with an internal monitor.
The internal monitor is an electronic wire that rests directly on the baby's head. The provider can place it on the baby's head during an internal exam. The internal monitor can only be used when the cervix is already open. This device provides a more accurate record of the baby's heart rate.
There are no special preparations needed for fetal monitoring.
External EFM poses no direct risks to the baby. However, because of being connected to the machine, the mother cannot walk around. This inactivity may prolong labor and reduce oxygen levels in the mother's blood, both of which can be detrimental to the unborn baby. Another problem is that electronic fetal monitoring seems to be associated with an increase in caesarian deliveries. There is a concern that EFM can give false alarms of distress in the baby, and that this can lead to unneeded caesarians. With internal monitoring, there is a higher risk for infection. For these and other reasons, the United States Preventive Services Task Force states that there is some evidence that using electronic fetal monitoring on low-risk women in labor might not be indicated. Many physicians, however, continue to use EFM routinely, and believe it to be of value in both low-risk and high-risk labors.
An unborn baby's heart rate normally ranges from 120-160 beats per minute (bpm). A baby who is receiving enough oxygen through the placenta will move around. The monitor strip will show the baby's heart rate rising briefly as he/she moves (just as an adult's heart rate rises when he/she moves).
The baby's monitor strip is considered to be reactive when the baby's heart rate rises at least 20 bpm above the baseline heart rate for at least 20 seconds. This must occur at least twice in a 20-minute period. A reactive heart rate tracing (also known as a reactive non-stress test) is considered a sign of the baby's well being.
If the baby's heart rate drops very low or rises very high, this signals a serious problem. In either of these cases it is obvious that the baby is in distress and must be delivered soon. However, many babies who are having problems do not give 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.
The first sign that a baby is not getting enough oxygen between contractions is often a drop in the baby's heart rate after the contraction (late deceleration). The baby's heart rate recovers to a normal level between contractions, only to drop again after the next contraction. This is also a more subtle sign of distress.
These babies will do fine if they are delivered in a short period of time. Sometimes, these signs develop long before delivery is expected. In that case, a C-section may be necessary.
Kripke, Clarissa C. "Why Are We Using Electronic FetalMonitoring?" American Family Physician May 1,1999.
Sweha, Amir, et al. "Interpretation of the Electronic FetalHeart Rate During Labor" American Family Physician May 1,1999.
Breech presentation— Fetal position in which the buttocks come first.
Cesarean section c-section— Delivery of a baby through an incision in the mother's abdomen instead of through the vagina.
Hypoxia— An oxygen deficiency.
Electronic Fetal Monitoring
Electronic Fetal Monitoring
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.
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
- 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.
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 heart-beat 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.
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.
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.
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.
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.
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.
Cunningham, Gary, et al. "Antepartum Assessment." In Williams Obstetrics, 2nd ed. McGraw-Hill Professional, 2005.
Jackson, David. "Fetal Distress in the Intrapartum Period." In Current Therapy in Obstetrics and Gynecology, 5th ed. Philadelphia: W.B. Saunders, 2000, 398-401.
The American College of Nurse-Midwives. 818 Connecticut Ave. NW, Suite 900, Washington, DC 20006. (202) 728-9860. 〈http://www.acnm.org〉.
American College of Obstetricians and Gynecologists. 409 12th St., S.W., PO Box 96920, Washington, DC 20090-6920. (202) 638-5577. 〈http://www.acog.org〉.
The Association of Women's Health, Obstetric and Neonatal Nurses (AWHONN). 2000 L Street, NW, Suite 740, Washington, DC 20036. (202) 261-1200. 〈http://18.104.22.168/index.html〉.
Society for Maternal-Fetal Medicine. 409 12th Street, SW, Washington, DC 20024. (202) 863-2476. 〈http://www.smfm.org/〉.
American College of Obstetricians and Gynecologists. "Fetal Heart Rate Patterns: Monitoring, Interpretation, and Management" In ACOG Technical Bulletin Number 207, (1995) Washington, DC.