Non-Reassuring Heart Tones
Also called fetal distres or non-reassuring fetal status, the theory of fetal distress is this:
Neurological damage occurs when the baby's brain is deprived of oxygen.
Lack of oxygen to the brain can be recognized by patterns in the baby's heart rate.
When the baby's heart rate pattern demonstrates a lack of oxygen (fetal distress) it is necessary for the baby to be born immediately.
To recognize changes in oxygenation, the baby's heart rate will be monitored, probably with an electronic fetal monitor (EFM) during labor for indications of fetal distress.
Why is Non-Reassuring Heart Tones a challenge?
Aside from the obvious concern that the baby is not handling labor well, the theory of fetal distress causes a cascade of challenges for the mother who desires to have a natural birth, even if she does not experience fetal distress during her labor.
To ensure your baby is safe during labor, his heart rate will be monitored. Your baby will be considered safe as long as his heart rate stays below 160 and above 100-120, and it does not become irregular. There are two ways to do this which operate equally well for the purposes of keeping babies safe. One, called intermittent auscultation, is to listen to the babies heart with a special stethoscope every 15 minutes. The other, called continuous monitoring, is to attach devices to the mother which allow a continuous printout of information about the baby's heart rate and mother's contractions.
Although the two methods do work equally well at keeping your baby safe, there are important differences. The first difference is that the electronic fetal monitor gives more information than the intermittent stethoscope method. But giving more information does not mean it gives better information, and certainly does not translate to better outcomes. It is the interpretation of the information that is open to the largest variation, which causes some problems. The biggest problem being cesarean surgery and operative vaginal births increase when the electronic fetal monitor is used, but the babies don't do any better than babies who had their heart rate measured every 15 minutes with a stethoscope.
The first challenge to families then, is that the theory of fetal distress has not held up to scientific scrutiny, despite the fact that it is a leading reason given for emergency cesarean surgery. Henci Goer makes the following points about the theory of fetal distress:
The baby's heart rate during labor correlates poorly with measures of the baby's condition at birth.
Measures of the baby's condition at birth correlate poorly with long-term outcomes.
Comparisons of EFM and intermittent listening show that EFM offers no long-term benefits in either low or high-risk pregnancies (although it may have short-term benefits especially when oxytocin is used).
Comparisons of EFM and intermittent listening show that EFM increases the likelihood of cesarean and vaginal instrumental delivery, infection and cerebral palsy in premature babies.
The second challenge is that because the theory of fetal distress is so well accepted, mothers giving birth in a hospital are almost always required to undergo monitoring with the electronic fetal monitor. Being attached to the monitor can be uncomfortable, limits the mother's mobility and as Henci Goer pointed out, increases the likelihood that the mother will "require" a cesarean.
Another challenge occurs if a caregiver feels the baby may be in fetal distress. Although studies have indicated that the monitor has a high false positive rate (says the baby is in distress when he is not), the mother who has been told her baby is in distress may be too concerned to remember that it may not be real. If the mother becomes upset, frightened or anxious she runs the risk of starting the fear-tension-pain cycle as well as being unable to be her own advocate. What is most unsettling is that many of the heart rate abnormalities are easily resolved with simple measures such as position changes, which the mother is hindered from doing while attached to the electronic fetal monitor.
Choose intermittent monitoring rather than continuous monitoring.
Avoid medications which can cause changes in the heart rate.
If the heart tones are non-reassuring, change position to see if the heart rate changes. You may also have success at resolving abnormal heart tones by interrupting the administration of oxytocin or by using oxygen for a few minutes. Double check the diagnosis with a more accurate monitor or by stimulating the baby's scalp before having a cesarean.
Things to discuss with your healthcare caregiver:
Since intermittent monitoring gives the same quality of information as continuous monitoring, you may want to discuss whether intermittent monitoring will be safe in your situation. If you expect to use medication for pain or to stimulate labor continuous monitoring may be required for safety.
Having a doula in labor can help you stay calm and focused if fetal distress becomes a concern. A doula can remind you of the high false positive rate for EFM and remind you to ask your caregiver about options for verifying the diagnosis (such as using an internal monitor or stimulating the baby's scalp). Knowing if it is true fetal distress can help you make informed decisions about how to proceed.
If you wish to avoid the potential negative effects of an EFM you may want to consider your options for giving birth in a birth center or at home.
If you do use continusous monitoring during labor, be sure to stay as upright and mobile as possible. Most monitor leads will give you two to four feet of space to move around it, so change your position regularly. Alternately, you may want to request the use of a telemetry unit which allows your baby's heart rate to be monitored without being attached to a wire.
Avoid the use of medications that affect the baby's heart rate as long as possible.
One further Note:
This information was posted in the July 2003 Newsletter for the American Society of Anesthesiologists:
"Fetal Distress" In 1988, ACOG recommended that the term "fetal distress" be abandoned (Committee Opinion No. 197) and recently voiced its concern about the continued use of the term as an antepartum or intrapartum diagnosis. The ACOG Committee on Obstetric Practice has reaffirmed that the term "fetal distress" is imprecise and nonspecific and has asked that the anesthesiology community be made aware that this term should not be used. The committee has suggested that the term be replaced with "nonreassuring fetal status" followed by a further description of findings (e.g., due to fetal bradycardia, late decelerations, etc.). Of note to anesthesiologists, the ACOG Committee Opinion No. 197 states that "performing a cesarean delivery for a nonreassuring fetal heart rate pattern does not necessarily preclude the use of regional anesthesia."
ACOG Technical Bulletin Number 132 - September 1989
Fawole B, Hofmeyr GJ. Maternal oxygen administration for fetal distress (Cochrane Review). In: The Cochrane Library, Issue 1, 2004. Chichester, UK: John Wiley & Sons, Ltd.
Leveno KJ, Cunningham FG, Nelson S, et al. A prospective comparison of selective and universal electronic fetal monitoring in 34,995 pregnancies. N Engl J Med 1986:615-9.
Thacker SB, Stroup D, Chang M. Continuous electronic heart rate monitoring for fetal assessment during labor (Cochrane Review). In: The Cochrane Library, Issue 1, 2004. Chichester, UK: John Wiley & Sons, Ltd.