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 15 bpm, 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 proposed terminology for a three-tiered system to replace the older, undefined terms. category i (normal): tracings with all these findings present are strongly predictive of normal fetal acid-base status at the time of observation and the fetus can be followed in a standard manner: baseline rate 110–160 bpm, moderate variability, absence of late or variable decelerations, early decelerations and accelerations may or may not be present. category ii (indeterminate): tracing is not predictive of abnormal fetal acid-base status. evaluation and continued surveillance and reevaluations are indicated. bradycardia with normal baseline variability tachycardia minimal or marked baseline variability of fhr accelerations: absence of induced accelerations after fetal stimulation periodic or episodic decelerations: longer than 2 minutes but shorter than 10 minutes; recurrent late decelerations with moderate baseline variability variable decelerations with other characteristics such as slow return to baseline, overshoots of "shoulders" seen (humps on either side of deceleration) category iii (abnormal): tracing is predictive of abnormal fetal acid-base status at the time of observation; this requires prompt evaluation and management. absence of baseline variability, with recurrent late/variable decelerations or bradycardia; or sinusoidal fetal heart rate. updated 2015 figo intrapartum fetal monitoring guidelines figo has recently modified the guidelines on intrapartum fetal monitoring, proposing the following interpretation: normal: no hypoxia or acidosis; no intervention necessary to improve fetal oxygenation state. baseline 110–160 bpm variability 5–25 bpm no repetitive decelerations (decelerations are defined as repetitive when associated with >50% contractions) suspicious: low probability of hypoxia/acidosis, warrants action to correct reversible causes if identified, close monitoring or adjunctive methods. lacking at least one characteristic of normality, but with no pathological features. pathological: high probability of hypoxia/acidosis, requires immediate action to correct reversible causes, adjunctive methods, or if this is not possible expedite delivery. in acute situations, delivery should happen immediately. baseline <100 bpm reduced or increased variability or sinusoidal pattern repetitive late or prolonged decelerations for >30 min, or >20 min if reduced variability (decelerations are defined as repetitive when associated with >50% contractions) deceleration >5 minutes benefits according to the cochrane review from february 2017, ctg was associated with fewer neonatal seizures but it is unclear if it had any impact on long-term neurodevelopmental outcomes. no clear differences in incidence of cerebral palsy, infant mortality, other standard measures of neonatal wellbeing, or any meaningful differences in long-term outcomes could be shown. continuous ctg was associated with the higher rates of caesarean sections and instrumental vaginal births. the authors see the challenge in how to discuss these results with women to enable them to make an informed decision without compromising the normality of labour. future research should focus on events that happen in pregnancy and labour that could be the cause of long-term problems for the baby.