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When Signals Become Crossed

Maternal-Fetal Signal Ambiguity

Cypher, Rebecca L., MSN, PNNP

The Journal of Perinatal & Neonatal Nursing: April/June 2019 - Volume 33 - Issue 2 - p 105–107
doi: 10.1097/JPN.0000000000000404
Departments: Legal Issues and Risk Management

President and Founder Cypher Maternal Fetal Solutions, LLC Gig Harbor, Washington

Disclosure: The author has disclosed that she has no significant relationships with, or financial interest in, any commercial companies pertaining to this article.

Each author has indicated that he or she has met the journal's requirements for Authorship.

As a clinician, a scenario presents with a woman in spontaneous labor who has entered transition. An electronic fetal monitoring (EFM) tracing reflected a category II tracing with a baseline rate of 180 beats per minute (bpm), minimal variability, no accelerations, and recurrent variable decelerations. Maternal vital signs included a normal respiratory rate and blood pressure, pulse rate averaging 115 bpm, and temperature of 99.6°F. Corrective measures such as position changes and intravenous fluid boluses were implemented, with little improvement in fetal status. When second-stage pushing commenced, a category I tracing with a baseline rate of 120 bpm, moderate variability, and periodic accelerations was observed. An infant was born an hour later with no signs of life and Apgar scores of 0, 0, and 0 at 1, 5, and 10 minutes. Aggressive neonatal resuscitation was futile, and the delivering team was left in a state of disbelief.

After this unexpected intrapartum fetal death, the words “we had no idea we were tracing the mother” were uttered by the clinical team during a debriefing. Tragically, nothing is worse than a pregnant woman presenting to labor and delivery with a seemingly healthy fetus and birthing an unexpected stillborn. This unfortunate outcome was a direct result of a fetal signal being interchanged with a maternal signal, also known as signal ambiguity or signal coincidence. Several months later, a malpractice claim was filed and eventually settled out of court for an undisclosed amount of money. While not an entirely rare situation, this heartbreaking outcome may have been preventable and may eventually lead to a malpractice claim.

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Assessing fetal well-being in an intrauterine environment requires surveillance devices that will detect, analyze, and display data via a fetal signal. Equipment capabilities, limitations, and troubleshooting strategies are important aspects of providing appropriate obstetric care because accurate interpretation is contingent on adequate signal output. Today's labor and delivery units have fetal monitoring equipment that utilizes Doppler signal processing technology. High-frequency ultrasound waves are transmitted to fetal tissues and are reflected back to a device that converts them into an electrical signal. Unfortunately, Doppler technology when used with EFM is prone to inadequate signal quality, maternal-fetal heart rate (FHR) misidentification, and artifact as there is higher signal loss when compared with internal monitoring. In other words, current EFM equipment can and will monitor and record a maternal heart rate that appears as an FHR pattern. Also, signal ambiguity may increase in frequency as more clinicians believe tracing interpretation can be accomplished from a remote location or not evaluated according to national guidelines. This is alarming as EFM's during intrapartum is to prevent significant fetal injury that may result from an oxygenation pathway interruption, not equipment malfunction or clinical error related to interpretation outside a patient's room.

Signal coincidence has been periodically reported in obstetric and biomedical equipment literature. In 2008, Neilson and colleagues1 published a case report of several clinical examples in which unexpected adverse outcomes occurred. These authors provided documentation that a signal source can transition between fetal and maternal heart rates with minimal or no data interruption. In fact, seasoned experts reviewing such cases could not determine at which point the FHR converted to a maternal heart rate.1 Consequently, these case report findings were communicated to the manufacturers and the United States Food and Drug Administration (FDA).

These concerning adverse outcomes related to inaccurate signal output brought maternal-fetal signal coincidence to the forefront in obstetric practice. In 2009, a class 2 device recall for Philips Avalon fetal monitors was issued by the FDA because of erroneous data and misinterpretation of FHR tracings. Additional events reported included switching between fetal and maternal heart rates, doubling and halving of cardiac activity, incongruity between audible and displayed heart rates, as well as erratic signals.2 Of note, these technical difficulties were not limited to one manufacturer or equipment model. In that same year, a “Dear Healthcare Provider” letter was also distributed in the United States by the FDA describing equipment problems.3 Philips also provided customers with information concerning recognition of signal ambiguity and FHR displays on monitoring equipment.2

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Collectively, a maternal-fetal dyad is subject to numerous alterations in extrinsic and intrinsic influences during the intrapartum period. These dynamic changes can impact fetal surveillance, signal output, and computer analysis of signals. Therefore, specific strategies can be utilized by clinicians to decrease the potential for simultaneous recording of fetal and maternal heart rates. First, if care providers are competent in intermittent auscultation with a fetoscope, simultaneous palpation of maternal pulse with auscultation can rule out signal ambiguity. Otherwise, when EFM commences, manual palpation of a maternal radial pulse rate is compared with FHR being emitted from bedside equipment, especially when external monitoring is in place. Alternatively, a spiral electrode may be placed, though obstetric providers must be aware that a maternal heart rate may be recorded when an intrauterine fetal death has occurred. Regardless, verifying a maternal heart rate can confirm or eliminate the presence of maternal-fetal coincidence. Perinatal best practice is to intermittently palpate a woman's pulse throughout labor.

If available, use of a tocodynamometer that allows for automatic maternal pulse detection using cross-channel verification may be considered. While automatic devices such as pulse oximeters and blood pressure equipment are frequently used in labor and delivery, such devices are still subject to error or malfunction. Both pieces of equipment can be affected by inappropriate placement, maternal movement, and positioning resulting in inaccurate results. This may limit reliability of data being collected for interpretation. Therefore, obtaining a radial pulse in conjunction with use of vital sign devices will assist in excluding signal coincidence. In addition, manual palpation with bedside documentation may demonstrate a clinician is attentive and focused on a laboring woman.

Another strategy is ensuring staff members involved with FHR interpretation receive continuing education on identification of potential signal ambiguity when EFM is utilized. A classic hallmark of this challenging pattern is maternal heart rate accelerations that are presumed to be FHR accelerations coinciding with uterine contractions or second-stage bearing down efforts (see Figure 1). From a cardiac perspective, a women's heart rate will respond to uterine activity with an elevated rate related to increased cardiac output, a release of catecholamines, and other autonomic responses related to pregnancy physiology. An FHR will characteristically react to oxygenation interruptions, such as contractions, with a deceleration response instead of an acceleration response. Also, maternal accelerations generally have higher amplitudes and longer durations than fetal accelerations.4 An additional definitive pattern associated with maternal-fetal coincidence is an abrupt change from an indeterminate or abnormal FHR pattern to a normal tracing. Physiologically, a category II tracing with a baseline rate of 165 bpm, minimal variability, absence of accelerations, and recurrent late decelerations will not return to a category I tracing suddenly, especially if corrective measures have not been implemented.

Figure 1

Figure 1

An additional pattern that can be included in fetal monitoring education is an understanding that in women with no risk factors, the mean maternal heart rate is significantly lower and mean variability is higher than what is observed in an FHR pattern. This was demonstrated in one study comparing simultaneous fetal and maternal heart rates. Authors found a significant difference between values. For example, mean maternal baseline rate in second stage was 83 bpm whereas fetal baseline rate was 134 bpm. Variability, described as maximal amplitude of peak to trough oscillations, was 13.7 bpm compared with fetal values of 8.3 bpm.5 Similarly, clinicians need to be alert for signal ambiguity in cases where a woman is tachycardic from conditions such as infection, hypovolemia anemic, or dehydration because a maternal heart rate may be undistinguishable from fetal data. Clinicians need to be mindful that with each tracing assessment, a unique maternal heart rate pattern may be recorded when continuous pulse oximetry is utilized. Maternal heart rate decelerations may appear on a recorded tracing. This unique cardiac pattern is highly suspicion for maternal hypovolemia.5

There are additional circumstances in which fetal and maternal heart rate misidentification may occur in clinical practice. These include maternal movement during ambulation when cableless monitoring surveillance systems are utilized, incorrect ultrasound transducer placement, and maternal body habitus. Prior to monitor placement, the number of fetuses, fetal positioning, and placental location are confirmed as these particular pregnancy features can factor into signal ambiguity.

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The current obstetric malpractice environment is essentially focused on optimal perinatal outcomes. Emphasis on providing reasonable and safe care is a priority in today's healthcare climate. The magnitude of simultaneous recording of fetal and maternal heart rates that go undetected impacts not only a family but also an entire healthcare team. Regrettably, an intrapartum demise from signal coincidence, followed by a malpractice claim, is what typically triggers risk management involvement, additional focused staff education on FHR misidentification, and policy changes. When a clinical team is proactive with building a solid foundation in maternal-fetal physiology and ongoing education in pattern recognition, interpretation, and equipment troubleshooting, there will be a decline in these tragic and preventable cases.

—Rebecca L. Cypher, MSN, PNNP

President and Founder

Cypher Maternal Fetal Solutions, LLC

Gig Harbor, Washington

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1. Neilson DR, Freeman RK, Mangan S. Signal ambiguity resulting in unexpected outcome with external fetal heart rate monitoring. Am J Obstet Gynecol. 2008;198(6):717–724.
2. Food and Drug Administration. Medical and radiation emitting devices, class 2 recall: Philips Avalon fetal monitor, December 17, 2009. Accessed December 18, 2018.
3. Food and Drug Administration. Philips Avalon fetal monitors: FDA safety communication. Published September 4, 2009. Accessed December 18, 2018.
4. Sherman DJ, Frenkel E, Kurzweil Y, Padua A, Arieli S, Bahar M. Characteristics of maternal heart rate patterns during labor and delivery. Obstet Gynecol. 2002;99(4):542–547.
5. Lappen JR, Chien EK, Mercer B. Contraction-associated maternal heart rate decelerations: a pragmatic marker of intrapartum volume status. Obstet Gynecol. 2018;132(4):1011–1017.
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