Tools of the Trade: What Does the Electronic Fetal Monitor Do?
When you are pregnant, your doctor might hook you up to a number of different machines (at some point or another) to check on your health and the baby’s. One of the tools doctors use is the electronic fetal monitor. All labor and delivery units are equipped with electronic fetal monitors. The monitor provides information regarding your baby’s heart rate and your contraction pattern. Physicians, midwives, and labor and delivery nurses receive specialized training in fetal monitoring. What they see on the monitor has a large impact on the care that is provided to you and your unborn baby.
Based on what is displayed on the electronic fetal monitor, each baby’s fetal heart rate pattern is analyzed and determined to be in one of three different categories. There are specific criteria that must be present for each category. The American College of Obstetricians and Gynecologists (ACOG) developed the categories to assist obstetricians, midwives, and labor and delivery nurses to better determine the overall well-being of the fetus. They are an added tool to be used before the baby is born to better determine which ones may be displaying the effects of not receiving enough oxygen and intervene when necessary.
Classifying your baby’s heart rate
There are three categories into which your baby might fall, based on the heart rate detected by the monitor:
A baby that meets the criteria based on the available information from the fetal monitor is most likely receiving enough oxygen. His/ her baseline heart rate is between 110 and 160 beats per minute with moderate variability (fluctuations between beats) and no variable or late decelerations. He/She may or not have accelerations in the heart rage, and there may be early decelerations present. Based on this criteria, he/she most likely has a normal acid-base balance in his or her body.
A baby that meets the criteria for this category is showing some signs that a problem in his/her acid-balance may be developing. He/She requires close observation by the labor and delivery staff, as well as interventions to correct whatever is occurring, such as turning the mom on her side, giving her extra IV fluid, or placing an oxygen mask on her face. If Pitocin is being administered, the rate of the infusion may be decreased or stopped.
The fetal monitor may show some variable or late decelerations, but the variability of the baby’s heart rate is normal, or the variability may be less than normal and display variable decelerations. Or, there may be no fluctuations in the heart rate, but there are no decelerations. His/Her heartrate may be too high, or he/she may have a deceleration of the heart rate that lasts more than 10 minutes (prolonged deceleration). It is unclear whether or not his/her acid-base balance has been affected; therefore, the fetal monitor strip must be watched closely. If interventions do not resolve the abnormalities present on the fetal monitor, the baby may need to be delivered.
Based on what is seen on the fetal monitor, the unborn baby may not be receiving enough oxygen, which will affect his/her acid-base balance. His/Her heart rate tracing may display no variability (fluctuations between beats), very little variability, or a baseline heartrate that is too slow. There may be variable or late decelerations that are occurring on a frequent basis, or the baby may display a sinusoidal heart rate pattern. Measures to correct the decrease in oxygen must be taken immediately, such as extra fluid given through the mom’s intravenous site, placing oxygen on the mom, and changing her position. If Pitocin infusing, it should be stopped. If the fetal heart rate pattern does not improve, the doctor should deliver the baby.
Understanding what “decelerations” mean
Many factors regarding what the electronic fetal monitor displays are analyzed to determine a baby’s status during labor. The labor and delivery staff analyze the beat-to-beat variability (fluctuations in the heart beat), accelerations (a rise in heartrate) and decelerations (a decrease in heart rate). If decelerations are present, the pattern regarding when they occur, how often they occur, and how low the heart rate drops, must be analyzed. There are four types of fetal heart rate decelerations:
- Spontaneous. There is a decrease in the fetal heart rate that is not related to a contraction.
- Early. There is a gradual decrease in heart rate that occurs at the same time as the peak (highest point) of the contraction. They normally appear when the woman is in active labor, and may result from pressure applied to the fetal head during a contraction. They are generally considered to be harmless unless they continue for a prolonged period of time, or there are indications based on the EFM that the baby is unable to tolerate them.
- Variable. There is an abrupt decrease in the baby’s heart rate. The time period from the beginning of the drop in heart rate to the lowest point of the heart rate is less than 30 seconds. Variable decelerations occur due to a partial slowing of blood through the baby’s umbilical cord. Chemoreceptors located in your baby’s cardiovascular system (heart) sense that the blood flow through the cord has decreased, and respond by lowering the heart rate.
Normally, the umbilical cord contains one vein and two arteries. The umbilical vein carries blood that contains oxygen to the baby. The two arteries transport blood, along with waste products, from your baby to the placenta. How well a baby tolerates this type of deceleration depends upon how low the heart rate drops, the variability (fluctuations) of the heart rate, how long it takes for the heart rate to return to the normal rate, and the length of time that the decelerations have occurred. Signs that a baby is unable to tolerate the decelerations include a decrease in variability, the overall heart rate is rising, and baby’s heart rate drops to an increasingly lower level.When variable decelerations are noted on the fetal monitor, interventions taken by the labor and delivery staff may lessen the frequency of the decelerations, how low the baby’s heart rate drops, and the duration of the deceleration. These interventions may include changing the mother’s position, infusing extra fluid through her intravenous line, and placing an oxygen mask on her face. If Pitocin is being infused through the IV, reducing the rate, or turning it off may be necessary. If the mother’s amniotic fluid sac has been broken, the variable decelerations may be caused by the umbilical cord being compressed between the baby and the uterine wall. The swimming pool of amniotic fluid that allowed the cord to float freely is no longer there. An intervention called an amnioinfusion may help the decelerations by adding additional fluid into the uterus, lessening the compression on the umbilical cord. If the interventions do not help, delivering the baby may be necessary before metabolic acidosis occurs. When a baby that has no other health issues begins to show signs (based on the electronic fetal monitor tracing) that he is not tolerating the decelerations, metabolic acidosis may occur within an hour and a half.1
- Late: There is a gradual decrease in the fetal heart rate, in which the heart rate is at its lowest after the peak (highest point) of a contraction. Late decelerations occur when there is a decrease in the amount of oxygen to the fetus. Steps must be taken to correct the cause of this type of deceleration if the cause is apparent, such as changing the mother’s position, giving the mother extra fluids through her intravenous line, or placing an oxygen mask on her face. If late decelerations are caused by a drop in the mother’s blood pressure, which may happen after she receives an epidural, medications can be given to raise her blood pressure. If late decelerations continue, especially when they are accompanied by a decrease in variability (fluctuations in the fetal heart rate), delivery by cesarean section may be necessary.
Complications arising from improper monitoring
During labor, the fetal heart monitor gives an indication of how well the fetus is tolerating the labor process, which, in turn, will determine the appropriate interventions that need to be taken. If the care provider does not recognize a non-reassuring fetal heart rate pattern, and impending hypoxia, the baby’s brain cells begin to die through the process of ischemia. At the time of birth, the baby may require resuscitation, such as chest compressions, and assistance with breathing. During the next 12 to 36 hours, the infant may begin to show signs of HIE, such as seizures, poor muscle tone, and feeding difficulties due to inability to coordinate sucking and swallowing.1
As the child grows, developmental delays will become more pronounced, leading to the need to be cared for throughout his or her lifetime. The diagnosis of HIE is made when there is evidence that the baby suffered from an insufficient supply of oxygen during the time that the mother was in labor, which is based on information gathered from electronic fetal monitoring and the results of umbilical cord gases.1 Many cases of HIE are preventable if appropriate care is initiated in a timely manner.
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- Parer, J., King, T., Flanders, S., Fox, M., & Kilpatrick, S. (2006). Fetal acidemia and electronic fetal heart rate patterns: is there evidence of an association? The Journal of Maternal-Fetal, and Neonatal Medicine, 19(5), 289-294. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/16753769