500px In the US, the Eunice Kennedy Shriver National Institute of Child Health and Human Development sponsored a workshop to develop a standardized nomenclature for use in interpreting Intrapartum fetal heart rate and uterine contraction patterns. This nomenclature has been adopted by the Association of Women's Health, Obstetric and Neonatal Nurses (AWHONN), the American College of Obstetricians and Gynecologists (ACOG), and the Society for Maternal-Fetal Medicine. The Royal College of Obstetricians and Gynaecologists and the Society of Obstetricians and Gynaecologists of Canada have also published consensus statements on standardized nomenclature for fetal heart rate patterns. Interpretation of a<unk>  tracing requires both qualitative and quantitative description of several factors. This is commonly summed up in the following acronym, DR C BRAVADO: *DR: Define Risk *C: Contractions (uterine activity) *BRA: Baseline fetal heart rate (FHR) *V: Baseline FHR variability *A: Presence of accelerations *D: Periodic or episodic decelerations *O: Changes or trends of FHR patterns over time Uterine activity There are several factors used in assessing uterine activity. *Frequency: the amount of time between the start of one contraction to the start of the next contraction. *Duration: the amount of time from the start of a contraction to the end of the same contraction. *Resting tone: a measure of how relaxed the uterus is between contractions. With external monitoring, this necessitates the use of palpation to determine relative strength. With an IUPC, this is determined by assessing actual pressures as graphed on the paper. *Interval: the amount of time between the end of one contraction to the beginning of the next contraction. The NICHD nomenclature defines uterine activity by quantifying the number of contractions present in a 10-minute window, averaged over 30 minutes. Uterine activity may be defined as: *Normal: 5 or fewer contractions in 10 minutes, averaged over a 30-minute window *Uterine tachysystole: more than 5 contractions in 10 minutes, averaged over a 30-minute window Baseline fetal heart rate The NICHD nomenclature defines baseline fetal heart rate as: Baseline FHR variability Moderate baseline fetal heart rate variability reflects the delivery of oxygen to the fetal central nervous system. Its presence is reassuring in predicting an absence of metabolic acidemia and hypoxic injury to the fetus at the time it is observed. In contrast, the presence of minimal baseline FHR variability, or an absence of FHR variability, does not reliably predict fetal acidemia or hypoxia; lack of moderate baseline FHR variability may be a result of the fetal sleep cycle, medications, extreme prematurity, congenital anomalies, or pre-existing neurological injury. Furthermore, increased (or marked) baseline FHR variability (see "Zigzag pattern" and "Saltatory pattern" sections below) is associated with adverse fetal and neonatal outcomes. Based on the duration of the change, increased (i.e. marked) baseline variability is divided into two terms: zigzag pattern and saltatory pattern of FHR. The NICHD nomenclature defines baseline FHR variability as: Zigzag pattern of fetal heart rate A Zigzag pattern of fetal heart rate (FHR) is defined as FHR baseline amplitude changes of more than 25 beats per minute (bpm) with a minimum duration of 2 minutes and maximum of 30 minutes. However, according to another study, even a >1 min duration of the zigzag pattern is associated with an increased risk of adverse neonatal outcomes. Despite the similarities in the shape of the FHR patterns, the zigzag pattern is distinguished from the saltatory pattern by its duration. According to the International Federation of Gynaecology and Obstetrics (FIGO), a saltatory pattern is defined as FHR baseline amplitude changes of more than 25bpm with durations of >30 minutes. In a recently published large obstetric cohort study of the zigzag pattern in almost 5,000 term deliveries in Helsinki University Central Hospital, Tarvonen et al. (2020) reported: "ZigZag pattern and late decelerations of FHR were associated with cord blood acidemia, low Apgar scores, need for intubation and resuscitation, NICU admission and neonatal hypoglycemia during the first 24 hours after birth." Furthermore, the "ZigZag pattern precedes late decelerations, and the fact that normal FHR pattern precedes the ZigZag pattern in the majority of the cases suggests that the ZigZag pattern is an early sign of fetal hypoxia, which emphasizes its clinical importance." Furthermore, in the recent study of 5150 deliveries, the hypoxia-related ZigZag pattern was associated with cord blood acidemia, low 5-min Apgar scores at birth, and need for neonatal resuscitation after birth, indicating increased occurrence of fetal hypoxia in GDM pregnancies. Saltatory pattern of fetal heart rate A saltatory pattern of fetal heart rate is defined in<unk>  <unk>  guidelines by FIGO as fetal heart rate (FHR) baseline amplitude changes of more than 25 beats per minute (bpm) with a duration of >30 minutes. In a 1992 study, the saltatory pattern FHR was defined by O'Brien-Abel and Benedetti as "fetal heart baseline amplitude changes of greater than 25bpm with an oscillatory frequency of greater than 6 per minutes for a minimum duration of 1 minute". The pathophysiology of the saltatory pattern is not well-known. It has been linked with rapidly progressing hypoxia, for example due to an umbilical cord compression, and it is presumed to be caused by an instability of the fetal central nervous system. In a study by Nunes et al. (2014), four saltatory patterns in<unk>  exceeding 20 minutes in the last 30 minutes before birth were associated with fetal metabolic acidosis. According to this study, saltatory pattern is a relatively rare condition; only four cases were found from three large databases. In a study by Tarvonen et al. (2019), it was demonstrated that the occurrence of saltatory pattern (already with the minimum duration of 2 minutes) in<unk>  tracings during labor was associated with fetal hypoxia indicated by high umbilical vein (UV) blood erythropoietin (EPO) levels and umbilical artery (UA) blood acidosis at birth in human fetuses. As saltatory patterns preceded late decelerations of fetal heart rate (FHR) in the majority of cases, saltatory pattern seems to be an early sign of fetal hypoxia. According to the authors, awareness on this gives obstetricians and midwives time to intensify electronic fetal monitoring and to plan possible interventions before fetal asphyxia occurs. Accelerations The NICHD nomenclature defines an acceleration as a visually apparent abrupt increase in fetal heart rate. An abrupt increase is defined as an increase from the onset of acceleration to the peak in 30 seconds or less. To be called an acceleration, the peak must be at least 15bpm, and the acceleration must last at least 15 seconds from the onset to return to baseline. A prolonged acceleration is greater than 2 minutes but less than 10 minutes in duration, while an acceleration lasting 10 minutes or more is defined as a baseline change. Before 32 weeks of gestation, accelerations are defined as having a peak of at least 10bpm and a duration of at least 10 seconds. Periodic or episodic decelerations Periodic refers to decelerations that are associated with contractions; episodic refers to those not associated with contractions. There are four types of decelerations as defined by the NICHD nomenclature, all of which are visually assessed. *Early decelerations: a result of increased vagal tone due to compression of the fetal head during contractions. Monitoring usually shows a symmetrical, gradual decrease and return to baseline of FHR, which is associated with a uterine contraction. A 'gradual' deceleration has a time from onset to nadir of 30 seconds or more. Early decelerations begin and end at approximately the same time as contractions, and the low point of the fetal heart rate occurs at the peak of the contraction. *Late decelerations: a result of placental insufficiency, which can result in fetal distress. Monitoring usually shows symmetrical gradual decrease and return to baseline of the fetal heart rate in association with a uterine contraction. A 'gradual' deceleration has an onset to nadir of 30 seconds or more. In contrast to early deceleration, the low point of fetal heart rate occurs after the peak of the contraction, and returns to baseline after the contraction is complete. *Variable decelerations: generally a result of umbilical cord compression, and contractions may further compress a cord when it is wrapped around the neck or under the shoulder of the fetus. They are defined as abrupt decreases in fetal heart rate, with less than 30 seconds from the beginning of the decrease to the nadir of heart rate. The decrease in FHR is at least 15 beats per minute, lasting at least 15 seconds but less than 2 minutes in duration. When variable decelerations are associated with uterine contractions, their onset, depth, and duration commonly vary with successive uterine contractions. *Prolonged deceleration: a decrease in FHR from baseline of at least 15bpm, lasting at least 2 minutes but less than 10 minutes. A deceleration of at least 10 minutes is a baseline change. Additionally, decelerations can be recurrent or intermittent based on their frequency (more or less than 50% of the time) within a 20 minute window. FHR pattern classification Before 2008, fetal heart rate was classified as either "reassuring" or "nonreassuring". The NICHD workgroup
Cardiotocography
Vectorcardiography
Electrical cardiometry
Holter monitor
Electrocardiography
Sphygmograph
Magnetocardiography
Electrocochleography