FIGO consensus guidelines on intrapartum fetal monitoring: Cardiotocography

The purpose of this chapter is to assist in the use and interpretation of intrapartum cardiotocography (CTG), as well as in the clinical management of specific CTG patterns. In the preparation of these guidelines, it has been assumed that all necessary resources, both human and material, required for intrapartum monitoring and clinical management are readily available. Unexpected complications may occur during labor, even in patients without prior evidence of risk, so maternity hospitals need to ensure the presence of trained staff, as well as appropriate facilities and equipment for an expedite delivery (in particular emergency cesarean delivery). CTG monitoring should never be regarded as a substitute for good clinical observation and judgement, or as an excuse for leaving the mother unattended during labor. The evidence for the benefits of continuous CTG monitoring, as compared with intermittent auscultation, in both low- and high-risk labors is scientifically inconclusive [1,2]. When compared with intermittent auscultation, continuous CTG has been shown to decrease the occurrence of neonatal seizures, but no effect has been demonstrated on the incidence of overall perinatal mortality or cerebral palsy. However, these studies were carried out in the 1970s, 1980s, and early 1990s where equipment, clinical experience, and interpretation criteria were very different from current practice, and they were clearly underpowered to evaluate differences in major outcomes [3]. These issues are discussed in more detail in Section 8 of this chapter. In spite of these limitations, most experts believe that continuous CTG monitoring should be considered in all situations where there is a high risk of fetal hypoxia/acidosis, whether due to maternal health conditions (such as vaginal hemorrhage and maternal pyrexia), abnormal fetal growth during pregnancy, epidural analgesia, meconium stained liquor, or the possibility of excessive uterine activity, as occurs with induced or augmented labor. Continuous CTG is also recommended when abnormalities are detected during intermittent fetal auscultation. The use of continuous intrapartum CTG in low-risk women is more controversial, although it has become standard of care in many countries. An alternative approach is to provide intermittent CTG monitoring alternating with fetal heart rate (FHR) auscultation. There is some evidence to support that this is associated with similar neonatal outcomes in low-risk pregnancies [4]. Intermittent monitoring should be carried out long enough to allow adequate evaluation of the basic CTG features (see below). The routine use of admission CTG for low-risk women on entrance to the labor ward has been associated with an increase in cesarean delivery rates and no improvement in perinatal outcomes [5], but studies were also underpowered to show such differences. In spite of the lack of evidence regarding benefit, this procedure has also become standard of care in many countries. Maternal supine recumbent position can result in aortocaval compression by the pregnant uterus, affecting placental perfusion and fetal oxygenation. Prolonged monitoring in this position should therefore be avoided. The lateral recumbent, half-sitting, and upright positions are preferable alternatives [6]. CTG acquisition can be performed by portable sensors that transmit signals wirelessly to a remote fetal monitor (telemetry). This solution has the advantage of allowing the mother to move freely during signal acquisition, rather than be restrained to bed or a sofa, and should therefore be the preferred option when available. Telemetry systems differ in the maximum distance allowed between patient and monitor for adequate signal transmission [7]. The horizontal scale for CTG registration and viewing is commonly called “paper speed” and available options are usually 1, 2, or 3 cm/min. In many countries throughout the world 1 cm/min is selected, while in the Netherlands it is usually 2 cm/min, and in North America and Japan it is almost exclusively 3 cm/min. Some experts feel that 1 cm/min provides records of sufficient detail for clinical analysis, and this has the advantage of reducing tracing length. Other experts feel that the small details of CTG tracings are better evaluated using higher papers speeds. The vertical scale used for registration and viewing may also be different, and available alternatives are 20 or 30 bpm/cm. The paper scales used in each center should be the ones with which healthcare professionals are most familiar, because tracing interpretation depends on pattern recognition and these patterns may appear very different. Inadvertent use of paper scales to which the staff is unaccustomed may lead to erroneous interpretations of CTG features. For example, at 3 cm/min variability appears reduced to a clinician familiar with the 1 cm/min scale, while it may appear exaggerated in the opposite situation (see examples below). External FHR monitoring uses a Doppler ultrasound transducer to detect the movement of cardiac structures. The resulting signal requires signal modulation and autocorrelation to provide adequate quality recordings [8]. This process results in an approximation of the true heart rate intervals, but this is considered to be sufficiently accurate for analysis. External FHR monitoring is more prone to signal loss, to inadvertent monitoring of the maternal heart rate (Fig. 1) [9], and to signal artefacts such as double-counting (Fig. 2) and half-counting [8], particularly during the second stage of labor. It may also not record fetal cardiac arrhythmias accurately. Maternal heart rate monitoring in the last 9 minutes of the tracing. External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). Double-counting of the fetal heart rate during decelerations (arrows). External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). Internal FHR monitoring using a fetal electrode (usually known as scalp electrode, but it can also be applied to the breech) evaluates the time intervals between successive heart beats by identifying R waves on the fetal electrocardiogram QRS complex, and therefore measures ventricular depolarization cycles. This method provides a more accurate evaluation of intervals between cardiac cycles, but it is more expensive because it requires a disposable electrode. It is very important that the fetal electrode is only applied after a clear identification of the presenting part and that delicate fetal structures such as the sutures and fontanels are avoided. Internal FHR monitoring requires ruptured membranes and has established contraindications, mainly related to the increased risk of vertical transmission of infections. It should not be used in patients with active genital herpes infection, those who are seropositive to hepatitis B, C, D, E, or to HIV [10,11], in suspected fetal blood disorders, when there is uncertainty about the presenting part, or when artificial rupture of membranes is inappropriate (i.e. an unengaged presentation). Fetal electrode placement should also preferably be avoided in very preterm fetuses (under 32 weeks of gestation). External FHR monitoring is the recommended initial method for routine intrapartum monitoring, provided that a recording of acceptable quality is obtained, i.e. that the basic CTG features can be identified. Minimum requirements for using this method are that careful repositioning of the probe is carried out during the second stage of labor, that in all atypical FHR tracings maternal heart rate monitoring is ruled out (see below), and if any doubt remains, fetal auscultation, ultrasound evaluation, or internal FHR monitoring are performed. If an acceptable record cannot be obtained with external monitoring or if a cardiac arrhythmia is suspected, then internal monitoring should be used, in the absence of the previously mentioned contraindications. External monitoring of uterine contractions using a tocodynamometer (toco) evaluates increased myometrial tension measured through the abdominal wall. Incorrect placement, reduced tension applied to the supporting elastic band, or abdominal adiposity may result in failed or inadequate registration of contractions. In addition, this technology only provides accurate information on the frequency of contractions. It is not possible to extract reliable information regarding the intensity and duration of contractions, nor on basal uterine tone. Internal monitoring of uterine contractions using an intrauterine catheter provides quantitative information on the intensity and duration of contractions, as well as on basal uterine tone, but it is more expensive as the catheter is disposable, and requires ruptured membranes. Contraindications include uterine hemorrhage of unknown cause and placenta previa. It may also be associated with a small risk of fetal injury, placental hemorrhage, uterine perforation, and infection [12]. The routine use of intrauterine pressure catheters has not been shown to be associated with improved outcomes in induced and augmented labor [13], and so it is not recommended for routine clinical use. Simultaneous monitoring of the maternal heart rate (MHR) can be useful in specific maternal health conditions and in cases where it is difficult to distinguish between maternal and fetal heart rates (for example complete fetal heart block) [9]. Some CTG monitors provide the possibility of continuous MHR monitoring, either by electrocardiography or pulse oximetry. In some recent models, the latter technology has been incorporated in the tocodynamometer, allowing continuous MHR monitoring without the use of additional equipment. Providing that the technology is available and does not cause discomfort to the mother, simultaneous MHR monitoring should be considered when performing continuous CTG, especially during the second stage of labor, when tracings show accelerations coinciding with contractions and expulsive efforts [9], or when the MHR is elevated. Continuous external FHR monitoring of twin gestations during labor should preferably be performed with dual channel monitors that allow simultaneous monitoring of both FHRs, as duplicate monitoring of the same twin may occur and this can be picked up by observing almost identical tracings. Some monitors have embedded algorithms to alarm when this situation is suspected. During the second stage of labor, external FHR monitoring of twins is particularly affected by signal loss, and for this reason some experts believe that the presenting twin should preferably be monitored internally for better signal quality [14], if no contraindications to fetal electrode placement are present. Other experts believe that external monitoring of both twins is acceptable, provided that distinct and good quality FHR signals can be obtained. All CTG tracings need to be identified with the patient name, place of recording, “paper speed,” and date and time when acquisition started and ended. In hospitals where paper CTG recordings are used, the latter should be considered as part of the patient record and preserved as such. In hospitals using digital CTG archives [15], a secure file backup system needs to be in place, and all tracings should be readily available for review by the clinical staff. CTG analysis starts with the evaluation of basic CTG features (baseline, variability, accelerations, decelerations, and contractions) followed by overall CTG classification. This is the mean level of the most horizontal and less oscillatory FHR segments. It is estimated in time periods of 10 minutes and expressed in beats per minute (bpm). The baseline value may vary between subsequent 10-minute sections. Normal baseline: a value between 110 and 160 bpm. Fetal behavioral state of active wakefulness. This pattern may lead to erroneously high baseline estimation if it is identified at the top of accelerations. External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). Preterm fetuses tend to have values toward the upper end of this range and post-term fetuses towards the lower end. Some experts consider the normal baseline values at term to be between 110-150 bpm. Tachycardia: a baseline value above 160 bpm lasting more than 10 minutes. Maternal pyrexia is the most frequent cause of fetal tachycardia, and it may be of extrauterine origin or associated with intrauterine infection. Epidural analgesia may also cause a rise in maternal temperature resulting in fetal tachycardia [17]. In the initial stages of a nonacute fetal hypoxemia, catecholamine secretion may also result in tachycardia. Other less frequent causes are the administration of beta-agonist drugs [18] (salbutamol, terbutaline, ritodrine, fenoterol), parasympathetic blockers (atropine, scopolamine), and fetal arrhythmias such as supraventricular tachycardia and atrial flutter. Bradycardia: a baseline value below 110 bpm lasting more than 10 minutes. Values between 100 and 110 bpm may occur in normal fetuses, especially in postdate pregnancies. Maternal hypothermia [19], administration of beta-blockers [20], and fetal arrhythmias such as atrioventricular block are other possible causes. Normal variability: a bandwidth amplitude of 5−25 bpm. Reduced variability: a bandwidth amplitude below 5 bpm for more than 50 minutes in baseline segments [21] (4, 5), or for more than 3 minutes during decelerations [22] (see 8, 9). Reduced variability. External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). Reduced variability. The baseline is affected by contractions causing decreases in fetal heart rate that are close to fulfilling the criteria for decelerations, but the bandwidth remains reduced. Internal fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). Reduced variability can occur due to central nervous system hypoxia/acidosis and resulting decreased sympathetic and parasympathetic activity, but it can also be due to previous cerebral injury [23], infection, administration of central nervous system depressants or parasympathetic blockers. During deep sleep, variability is usually in the lower range of normality, but the bandwidth amplitude is seldom under 5 bpm. There is a high degree of subjectivity in the visual evaluation of this and therefore careful is recommended in an normal CTG, reduced variability due to is very to occur during labor without or decelerations and a rise in the variability a bandwidth value bpm lasting more than 30 minutes (Fig. variability: Internal fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). The of this pattern is but it may be with decelerations, when hypoxia/acidosis very It is to be by fetal system to in less than 30 in FHR above the of more than bpm in and lasting more than but less than 10 minutes. accelerations with fetal and are a of a that does not have 32 weeks of amplitude and frequency may be lower and 10 bpm of with the of fetal behavioral accelerations occur during periods of deep sleep, which can last up to 50 minutes The absence of accelerations in an normal intrapartum CTG is of but it is to coinciding with uterine contractions, especially in the second stage of labor, possible erroneous recording of the maternal heart the FHR more with a while the maternal heart rate [9]. decelerations that are with normal variability the and are with contractions. are to be by fetal compression and not fetal decelerations decelerations that a to in less than 30 good variability the to the and to uterine contractions (Fig. Internal fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). decelerations the of decelerations during labor, and they a to increased as occurs with compression are seldom associated with an important degree of fetal hypoxia/acidosis, they to a reduced variability the (see decelerations below), duration 3 minutes (see decelerations below). decelerations with reduced decelerations with a a to the baseline reduced variability the (Fig. and occurs when more than 30 between the of a and When contractions are decelerations more than 20 after the of a have a after the and a to the baseline after the end of the decelerations in the second of the tracing. External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). These decelerations are of a to fetal In the presence of a tracing with no accelerations and reduced variability, the of decelerations also those with an amplitude of bpm. Prolonged lasting more than 3 minutes. These are to include a and to 5 with FHR at less than bpm and reduced variability the (Fig. are associated with fetal hypoxia/acidosis and Prolonged External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). a with an amplitude of and a frequency of per This pattern more than 30 and with accelerations (Fig. External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). The of the pattern is but it occurs in with fetal as is in hemorrhage, and ruptured previa. It has also been in cases of fetal infection, cardiac and pattern the but with a more rather than the (Fig. duration seldom 30 minutes and it is by normal patterns and External fetal heart rate monitoring at 1 cm/min (top graph), 2 cm/min (middle graph), and 3 cm/min (bottom graph). This pattern has been after administration to the mother, and during periods of fetal and other It is difficult to distinguish the pattern from the true leaving the duration of the as the most important to between the This to periods of fetal deep alternating with periods of active and The occurrence of different behavioral is a of fetal and absence of can last up to 50 minutes [21] and is associated with a very accelerations, and variability. is the most frequent behavioral and is by a of accelerations and normal variability. is and by a of accelerations and normal variability (Fig. In the latter accelerations may be so frequent as to cause in baseline estimation (see between the different patterns become after weeks of to fetal nervous system These are in the uterine signal followed by with in This an excessive frequency of contractions and is as the occurrence of more than contractions in 10 in successive 10-minute or a requires a previous evaluation of basic CTG features (see should be of or to the criteria in Other systems a of are recommended by some experts to the of CTG signals during labor, of the tracing should be carried out at 30 minutes. and to the mother, can FHR features (see so CTG analysis needs to be with other clinical information for a interpretation and adequate a if the to a baseline and a variability, the risk of to the central is very However, the that should clinical management are in When fetal hypoxia/acidosis is or suspected and and is required to neonatal this does not mean an cesarean delivery or vaginal The cause for the of the pattern can be identified and the situation with subsequent of adequate fetal and the to a normal tracing. uterine is the most frequent cause of fetal hypoxia/acidosis and it can be detected by in the CTG tracing the uterine It can usually be by reducing or if with (salbutamol, terbutaline, or During the second stage of labor, maternal efforts can also to fetal hypoxia/acidosis and the mother can be to the situation is compression can occur in the supine position and lead to reduced placental uterine may also be associated with the supine position due to the of the by the uterine In these the mother to is followed by of the CTG compression is cause of CTG and these can be by the maternal position or by performing maternal can also occur during labor, usually after epidural or analgesia and it is usually by administration an Other less frequent complications affecting the maternal maternal or the fetal can also result in fetal hypoxia/acidosis and management is the of this administration to the mother is used with the of fetal and CTG but there is no evidence from clinical that this when performed in is when maternal is adequate are also commonly used for the purpose of CTG but there is no evidence from clinical to that this is in women clinical is required to the cause for a or CTG, to the of the conditions with which it is and to the of with the of fetal hypoxia/acidosis, as well as may be used to evaluate fetal When a or CTG pattern is the cause should be a tracing If the situation does not and the pattern to needs to be for evaluation or delivery if a pattern During the second stage of labor, due to the additional effect of maternal hypoxia/acidosis may more should be to the of maternal and if there is no delivery should be has limitations, and it is necessary to be of these for use of the It has been well demonstrated that CTG analysis is to and even when use The that are prone to are the identification and of decelerations, the evaluation of variability and the of tracings as and The subjectivity of analysis has also been demonstrated in of where CTG features are to be more abnormal in cases with known neonatal studies have evaluated the of and to the occurrence of CTG interpretation different intervals between tracing and and different criteria to have been used, resulting in However, it is that hypoxia/acidosis has not been after a normal CTG tracing. the other and tracings have a to and i.e. a of cases with and tracings not have these outcomes there is a between FHR patterns and hypoxia/acidosis, to between with or without is they are but have a and However, it should not be that the of intrapartum fetal monitoring is to situations that so as to fetal The subjectivity of CTG interpretation and the that is a that may not the of or injury are important to these of have been continuous CTG monitoring with intermittent as for fetal hypoxia/acidosis during labor, in both low- and high-risk women [1,2]. However, these place in the 1970s, 1980s, and early and used different CTG interpretation so it is difficult to results to current clinical these in they a of continuous CTG for fetal monitoring in all women during labor, as the only improvement a in neonatal not evaluated in most and no differences were in the of overall perinatal mortality and cerebral palsy. However, it is that the were underpowered to detect differences in these outcomes [3]. a small of perinatal and cerebral are by intrapartum hypoxia/acidosis, so a of cases are to show any the other continuous CTG associated with a increase in cesarean delivery and a increase in vaginal additional for the mother and and the may result from CTG of the of fetal and inadequate clinical It is for clinical need to be as and as to allow even in and In addition, and of the labor ward staff is to ensure use of this The have no of to