- High-risk pattern. Fetuses at greatest risk include those with marked bradycardia, recurrent late and variable decelerations, and absent variability.
- Normal pattern. In contrast, a normal baseline rate with normal, moderate variability and accelerations, and absence of periodic patterns (decelerations) predicts fetal well-being.
- Tips on interpretation. Deciphering fetal heart rate patterns entails making observations over time. Many patterns acquire increased significance when there is a trend toward persistent, significant departures from baseline with decreased variability, loss of accelerations, or persistent episodic or periodic decelerations, particularly with loss of variability.
True or false: Electronic fetal monitoring reduces the incidence of cerebral palsy and infant morbidity and mortality.
Unfortunately, the statement is false, although patients continue to believe it is true. As a result, a large proportion of obstetrics liability cases center on electronic fetal monitoring (EFM): 43% of all lawsuits alleging obstetric malpractice, 52% of cases involving a stillborn fetus or neonatal death, and 66% of cases involving a neurologically impaired infant.1
Although the reliability and validity of EFM in reducing perinatal morbidity and mortality leave much to be desired, they could be greatly improved by increasing our understanding of the physiologic causes of patterns, establishing formal definitions for the various fetal heart rate (FHR) patterns, and developing specific recommendations for “abnormal” patterns.
Once these goals are attained, the question of whether EFM can be used to prevent asphyxial brain damage can be more adequately addressed.
This article discusses the following topics:
- EFM patterns and their importance,
- key research findings to date, and
- how to identify patients at greatest risk of an adverse outcome.
Unfulfilled hopes based on flawed assumption
Evaluation of the FHR in labor—first by auscultation and then by continuous EFM—has long held promise of improved outcomes. As early as the 1800s, auscultated Electronic fetal monitoring: The difficulty of linking patterns with outcomes FHR decelerations and prolonged bradycardias were seen as signs of fetal distress in labor. When criteria were being developed for obstetric intervention with forceps in the late 1800s, tachycardia was included as an indication, building the foundation for contemporary definitions of nonreassuring FHR patterns.
Many decades later, abnormal FHR patterns correlated with low Apgar scores and neonatal death (although the correlation between certain patterns and poor outcomes was weak) in the findings of the American Collaborative Perinatal Study,2 which reviewed 25,000 births monitored using intermittent auscultation from 1959 through 1965.
The largely flawed assumption that most cases of cerebral palsy are caused by intrapartum asphyxia led to a concerted effort to decrease the incidence of asphyxia through EFM. By the 1970s, the expectation was that EFM would decrease perinatal morbidity and mortality.
Since its introduction into clinical practice in the early 1970s, EFM has become increasingly common; its use grew from 61% of women giving birth in 1989 to 84% in 1998.3
Findings of randomized controlled trials. The first randomized controlled trial4 of EFM in labor, in 1976, demonstrated no improvement in outcome but a significant increase in surgical births; later trials showed no decrease in perinatal mortality or cerebral palsy.
The 1985 Dublin trial,5 which scored the highest in study design in a later meta-analysis, showed a slight protective effect of EFM overall.
A 1995 meta-analysis6 of 12 randomized controlled trials encompassing 58,555 pregnancies identified 9 outcomes, including Apgar scores, perinatal mortality, and neonatal seizures. EFM had a consistent impact only on neonatal seizures, and had no measurable effect on morbidity and mortality. Overall, 1.1% of neonates in the auscultated group had seizures, compared with 0.8% in the EFM group. Operative deliveries also increased in the EFM group.
EFM effects on neonatal outcomes. Freeman7 summarized the gains of EFM from 1972 to 1990 as follows:
- no effect on cerebral palsy,
- no effect on neonatal morbidity, and
- no improvement in neurologic outcomes in premature infants.
In 1995, Vintzileos and colleagues8 studied fetal acidemia in 680 auscultated labors and compared them with 739 monitored by EFM, using umbilical artery pH of less than 7.15 as an outcome measure. EFM was superior to auscultation, with better sensitivity and higher positive and negative predictive value.
Identification of patterns still rests on visual interpretation
In 1997, after a workshop to develop standardized, unambiguous definitions for fetal heart tracings, the National Institute for Child Health and Human Development (NICHD) issued guidelines for interpreting EFM9; these focus on visual interpretation, though computerized analyses are being developed. The definitions emphasize intrapartum evaluation, and the major patterns are categorized as baseline, periodic, or episodic.
Variability is defined by amplitude and includes short-term (beat to beat) and long-term variability, with no distinction between the two. Sinusoidal patterns are excluded from the definition.