CLINICAL OBSTETRICS AND GYNECOLOGY Volume 58, Number 2, 263–268 Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
Intrapartum Fetal Monitoring ALISON G. CAHILL, MD, MSCI, and JANINE SPAIN, MD Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri Abstract: Intrapartum fetal monitoring to assess fetal well-being during the labor and delivery process has been a central component of intrapartum care for decades. Today, electronic fetal monitoring (EFM) is the most common method used to assess the fetus during labor without substantial evidence to suggest a benefit. A Cochrane review of 13 trials, which included over 37,000 women, found that continuous EFM provided no significant improvement in perinatal death rate [risk ratio (RR) 0.86; 95% confidence interval (CI), 0.59-1.23] or cerebral palsy rate (RR 1.75; 95% CI, 0.84-3.63) as compared with intermittent auscultation; however, there was a significant decrease in neonatal seizures (RR 0.50; 95% CI, 0.31-0.80). In addition, there was a significant increase in cesarean delivery (RR 1.63; 95% CI, 1.29-2.07) and operative vaginal delivery (RR 1.15; 95% CI, 1.011.33). Despite the lack of scientific support to suggest that EFM reduces adverse neonatal outcomes, its use is almost universal in the hospital setting and very likely has contributed to the rise in cesarean rate. Key words: electronic fetal monitoring, labor and delivery, assessment, acidemia
electronic fetal monitoring. It is also important that providers both speak and document using the nomenclature system put forth by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) as well as adopt common approaches to patterns seen clinically.2 Electronic fetal monitoring (EFM) is almost universal at most institutions in the United States. It is accomplished either noninvasively with a small ultrasound-based device placed on the maternal abdomen, or invasively with a small scalp electrode place on the fetal head. Either device provides real-time fetal heart rate pattern information to the providing team. Unfortunately, after introduction around 1970,3 EFM gain wide-spread use before scientific evidence existed to support it. To date, the randomized trials comparing EFM to intermittent auscultation (the historical alternative) have not provided evidence for benefit but did suggest that the use of EFM increased the risk of operative delivery.4 Vintzileos and colleagues found no difference in 1-minute and 5-minute Apgar scores, fetal acidosis at birth, need for neonatal resuscitation, or any other neonatal complications between those randomized to continuous EFM versus intermittent
One of the most common indications for a primary cesarean is ‘‘non-reassuring fetal heart rate patterns.’’1 Given that such a diagnosis is made at the bedside, it is imperative that obstetric providers understand the strengths and limitations of Correspondence: Alison G. Cahill, MD, Department of Obstetrics and Gynecology, Washington University School of Medicine in St. Louis, MSCI, St. Louis, MO. E-mail: [email protected]
The authors declare that they have nothing to disclose. CLINICAL OBSTETRICS AND GYNECOLOGY
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auscultation. They did identify a higher rate of cesarean delivery for suspected fetal distress (5.3% vs. 2.3%, P = 0.005) and vacuum extraction (5.8% vs. 2.4%, P = 0.002).5 Similarly, Leveno an colleagues compared use of continuous EFM in all pregnancies versus only pregnancies deemed to be high risk. They found universal monitoring was associated with a significant increase in the rate of cesarean delivery for fetal distress but found no difference in rate of intrapartum stillbirth, low Apgar scores, need for assisted ventilation, admission to intensive care nursery, or neonatal seizures.6 Despite this, EFM is the most commonly used tool in obstetrics,7 with no evidence for benefit and the potential for harm. The currently accepted taxonomy, endorsed by the American College of Obstetricians and Gynecologists (ACOG),8 divides all patterns of EFM into 3 categories: category I (normal), category II (indeterminant), and category III (abnormal). Knowing the rate of first cesareans performed for the indication of ‘‘non-reassuring fetal heart rate parameters,’’1 and the rarity of category III patterns, category II likely represents the majority of tracings for which providers decide to intervene with cesarean. Unfortunately, there are no published data to support an association between category II patterns and neonatal outcomes. Thus, 1 important consideration for providers who are making the diagnosis of nonreassuring fetal status with the intent to proceed with cesarean is to assure that all possible clinically indicated measures have been employed to resolve the elements of the category II tracing that are raising concern for fetal well-being. The utility of additional measures, such as protocols for proceeding to a cesarean for a category II pattern, or formalized ‘‘double-checks’’ have yet to be investigated. Category I patterns are considered normal and do not require intervention. However, on-going assessment is important because patterns can change over www.clinicalobgyn.com
time. Moderate variability and presence of accelerations,9,10 features of category I patterns, have both been associated with normal neonatal umbilical cord blood pH (Z7.20). The majority of intrapartum fetal heart rate tracings are category II.11,12 There are, however, specific elements of category II patterns, such as tachycardia, bradycardia, absent or minimal variability, absence of accelerations, and late or prolonged decelerations, which have been associated with acidemia.11,13–18 Prior studies have attempted to further subcategorize category II tracings into 3 different tiers based on the presumed threat of fetal acidemia. However, the use of additional subcategories within the NICHD category II pattern has not yet been demonstrated to have a clinically significant effect on neonatal outcomes.19,20 Despite certain category II features being associated with acidemia, as with category III patterns, these elements of category II tracings have a low-positive predictive value for acidemia or adverse outcomes.12 There are some interventions recommended for particular components of category II tracings. Recurrent variable decelerations, thought to be a physiologic response to repetitive compression of the umbilical cord, are not themselves pathologic. However, their frequency without resolution can lead to acidemia over time. A recent study found that the total deceleration area (depth duration) in the 30minute preceding delivery had the best predictive ability for fetal acidemia over repetitive late decelerations, repetitive prolonged decelerations, repetitive variable decelerations, or tachycardia.12 Additional work needs to be done to understand the association between EFM patterns like these, which are outside the NICHD framework, and their clinical usefulness. Amnioinfusion with normal saline has been demonstrated to both resolve recurrent variable decelerations21–23 as well as to reduce the incidence of cesarean for
Intrapartum Fetal Monitoring nonreassuring fetal parameters.23–25 Similarly, other elements of category II fetal heart rate tracings associated with a differential that includes acidemia, such as minimal variability or recurrent late decelerations, should be approached with in utero resuscitation that includes maternal position change. In these settings, the absence of fetal acidemia can be easily tested with scalp stimulation if the cervix is dilated. In the setting of EFM patterns raising concern for acidosis, such as minimal or absent variability, digital fetal scalp stimulation that yields a fetal heart rate acceleration is highly sensitive for the absence of acidosis (pHZ7.20).10,26 Vibroacoustic stimulation is a reasonable alternative to digital scalp stimulation under clinical circumstances that prohibit scalp stimulation, such as a closed cervix.27 However, if EFM patterns concerning for acidosis persist, repeat testing is necessary. Historically, fetal scalp sampling for pH measurement during labor was a routine part of clinical practice but is no longer performed in much of the United States. Investigators have proposed the use of scalp sampling for fetal lactate, as opposed to pH, but studies to date do not support either to be a superior test to identify fetuses at risk for clinically meaningful morbidity.28–32 A recent systematic review highlighted that older evidence, although limited, did suggest that the use of fetal scalp sampling could reduce that risk of operative delivery.33 However, in the United States today, the equipment to test fetal scalp samples is not longer available. Thus, we will likely need future evidence from scientists outside the United States to provide guidance regarding the potential role of scalp sampling in labor in modern obstetric practice. Prolonged decelerations (lasting >2 but 5 contractions in 10 minutes averaged over 30 minutes, can occur spontaneously or in the setting of contractile agents, and can be associated with fetal heart rate changes such as prolonged or recurrent decelerations. Cessation or reduction of the contractile agent, or administration of a b-mimetic, are all reasonable approaches to improve the fetal heart rate tracing and are recommended by ACOG.36,37 There are no current data to support intervention specifically for decelerations with atypical features, an element of category II, as they have not been associated with acidemia.38 Recurrent variable decelerations, thought to be due to the fetal physiologic response to umbilical cord compression, are amenable to amnioinfusion (AI). AI, accomplished by infusing normal saline into the uterus via an intrauterine pressure catheter, has been shown to decrease the persistence of repetitive decelerations and also the risk of cesarean for nonreassuring fetal parameters.22,24 Category III fetal heart rate tracings during labor require intervention.39 Elements of category III patterns,40 including absent variability with recurrent late or variable fetal heart rate decelerations, or bradycardia, or a sinusoidal pattern, have been associated with abnormal arterial pH, encephalopathy, and cerebral palsy.11,16,41,42 Although category III patterns are not predictive of acidemia or adverse outcomes,41 their association necessitates intervention. Intrauterine resuscitative efforts, including maternal repositioning and oxygen supplementation, assessment for hypotension and tachysystole that may be corrected, and evaluation for other explanatory events such as cord prolapse, abruption, or uterine rupture, should be performed swiftly and the duration should be limited. ACOG recommends preparations for imminent delivery in the event that intrauterine resuscitative measures do not www.clinicalobgyn.com
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improve the fetal heart rate pattern. As no data are currently available to specify the optimal mode of delivery, it should be chosen based on the expertise of the provider and the available resources. Two studies of cases of uterine rupture after prior cesarean found that neonates delivered within 18 minutes after a suspected uterine rupture had normal umbilical blood pH levels and no significant neonatal morbidity.34,36 Historically, it has been suggested that delivery for concerning fetal status be performed within 30 minutes of the decision to intervene but published data do not support this standard.43,44 Although swift delivery remains recommended, this should be weighed against the incumbered competing maternal risks in the setting of emergency surgery. Alternatives and adjunct tools to EFM have been proposed. Fetal pulse oximetry seemed to be a safe and minimally invasive way to directly measure fetal oxygenation in labor and reduce unnecessary cesareans, as suggested by early studies.45–47 However, a large, multicenter randomized controlled trial of fetal pulse oximetry by the Maternal-fetal Medicine Units Network demonstrated no reduction in cesarean or cesarean for nonreassuring fetal parameters when pulse oximetry was used.48 With no evidence for benefit, fetal pulse oximetry was not FDA approved and is not used in clinical practice. Recently, ST segment waveform analyzer (STAN) has been suggested as an adjunct to EFM, based on animal and adult data that suggest the ST waveform changes under hypoxic conditions. Early studies produced conflicting results regarding whether the use of STAN could reduce risk of acidosis or risk of operative delivery for nonreassuring fetal parameters.49–52 A Cochrane meta-analyses in 2012 demonstrated that published evidence did not support the use of STAN because there was no significant reduction in cesarean, acidosis, or neonatal encephalopathy.53 Large, multi-center trials are ongoing to test www.clinicalobgyn.com
the ability of STAN in modern obstetrics to reduce adverse outcomes but currently there is not place for STAN in evidence-based clinical practice. The most important guiding principal is to interpret the fetal heart rate patterns within the clinical setting. Medication exposure, regional anesthesia placement and dosage, labor progress, cervical examination, infection, terminal events, and maternal physiologic parameters can all impact the fetal heart rate pattern. Remediation or awareness of such factors will assist in the clinical decision-making regarding the fetal heart rate pattern and the true risk of acidemia in a given patient. Further, based on the epidemiologic data reporting the cesarean rate and that describing indications for cesarean would indicate that the diagnosis of nonreassuring fetal status is made too often. It is prudent that obstetric providers understand the limitations of EFM and make efforts to assess fetal well-being using strategies such as scalp stimulation before concluding that a cesarean for nonreassuring fetal status is warranted.
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