Pathophysiological interpretation of fetal heart rate tracings in clinical practice.

The onset of regular, strong, and progressive uterine contractions may result in both mechanical (compression of the fetal head and/or umbilical cord) and hypoxic (repetitive and sustained compression of the umbilical cord or reduction in uteroplacental oxygenation) stresses to a human fetus. Most fetuses are able to mount effective compensatory responses to avoid hypoxic-ischemic encephalopathy and perinatal death secondary to the onset of anaerobic metabolism within the myocardium, culminating in myocardial lactic acidosis. In addition, the presence of fetal hemoglobin, which has a higher affinity for oxygen even at low partial pressures of oxygen than the adult hemoglobin, especially increased amounts of fetal hemoglobin (ie, 180-220 g/L in fetuses vs 110-140 g/L in adults), helps the fetus to withstand hypoxic stresses during labor. Different national and international guidelines are currently being used for intrapartum fetal heart rate interpretation. These traditional classification systems for fetal heart rate interpretation during labor are based on grouping certain features of fetal heart rate (ie, baseline fetal heart rate, baseline variability, accelerations, and decelerations) into different categories (eg, category I, II, and III tracings, "normal, suspicious, and pathologic" or "normal, intermediary, and abnormal"). These guidelines differ from each other because of the features included within different categories and because of their arbitrary time limits stipulated for each feature to warrant an obstetrical intervention. This approach fails to individualize care because the "ranges of normality" for stipulated parameters apply to the population of human fetuses and not to the individual fetus in question. Moreover, different fetuses have different reserves and compensatory responses and different intrauterine environments (presence of meconium staining of amniotic fluid, intrauterine inflammation, and the nature of uterine activity). Pathophysiological interpretation of fetal heart rate tracing is based on the application of the knowledge of fetal responses to intrapartum mechanical and/or hypoxic stress in clinical practice. Both experimental animal studies and observational human studies suggest that, just like adults undertaking a treadmill exercise, human fetuses show predictable compensatory responses to a progressively evolving intrapartum hypoxic stress. These responses include the onset of decelerations to reduce myocardial workload and preserve aerobic metabolism, loss of accelerations to abolish nonessential somatic body movements, and catecholamine-mediated increases in the baseline fetal heart rate and effective redistribution and centralization to protect the fetal central organs (ie, the heart, brain, and adrenal glands), which are essential for intrauterine survival. Moreover, it is essential to incorporate the clinical context (progress of labor, fetal size and reserves, presence of meconium staining of amniotic fluid and intrauterine inflammation, and fetal anemia) and understand the features suggestive of fetal compromise in nonhypoxic pathways (eg, chorioamnionitis and fetomaternal hemorrhage). It is important to appreciate that the timely recognition of the speed of onset of intrapartum hypoxia (ie, acute, subacute, and gradually evolving) and preexisting uteroplacental insufficiency (ie, chronic hypoxia) on fetal heart rate tracing is crucial to improve perinatal outcomes.

Does the saltatory pattern on cardiotocograph (CTG) trace really exist? The ZigZag pattern as an alternative definition and its correlation with perinatal outcomes.

BACKGROUND: The saltatory pattern (SP) has been defined by guidelines as a uniformly increased bandwidth of >25 beats per min lasting for 30 min. However, previous research suggest that it is very unusual to observe such a "uniform" increase in the bandwidth persisting for >30 min. Baseline fetal heart rate variability (FHRV) on cardiotocography reflects the integrity of the central nervous system. During labor, in the presence of a gradually-evolving hypoxia associated with the onset of metabolic acidosis, FHRV may be reduced. However, if a fetus is exposed to rapidly-evolving hypoxia, it may not have sufficient time to release catecholamines and the perfusion of central organs can be impaired. In such cases, simultaneous increased activity of the sympathetic nervous system to obtain more oxygen as well as enhanced parasympathetic activity to reduce the myocardial workload can lead to autonomic instability. This exaggerated autonomic response can be seen frequently on the cardiotocograph as a rapid, irregular, abrupt "up and down" fluctuation across the baseline (amplitude >25 beats per min). The authors have termed this pattern as "ZigZag" when apparent for a minimum of 1 min. It differs from the SP in terms of duration and uniformity of the bandwidth. OBJECTIVE: To determine the incidence of the SP during labor as well as a shorter and less uniform version of the SP newly called "ZigZag pattern" (ZZP). The intention was to correlate them with perinatal outcomes, taking into account the duration of the ZZP. STUDY DESIGN: A retrospective analysis of 500 consecutive cardiotocograph traces was performed to identify saltatory patterns and ZigZag patterns of 1 and 2 min of duration. Apgar scores, umbilical cord pH values and admission to the Neonatal Unit were evaluated and correlated with the cardiotocograph findings. RESULTS: Not a single case of the SP was observed. A ZZP of 1 min of duration (ZZP1) was identified in 30.1% of the CTG during the last hour prior to delivery; ZZP lasting for 2 min (ZZP2) were identified in 8.9% of cases during the same period. Apgar scores at 1 min of ≤7 were significantly more frequent in newborns where the ZZP was observed (36.7% in ZZP1 and 54.5% in ZZP2 versus 9.5% in fetuses without); similarly, the Apgar scores at 5 min of ≤7 were also more frequent when ZZP was observed (6.7% in ZZP1 and 13.6% in ZZP2 versus 1.1% in controls). Moderate acidosis (pH 7.0-7.10) was more common in fetuses with the ZZP (14.3% in ZZP1 and 15% in ZZP2) compared to those without (4.6 and 7.2%, respectively). Similarly, mild acidosis (pH 7.1-7.2) was more common with the ZZP (40.3% in ZZP1 and 35% in ZZP2 versus 27.6 and 31.7%, respectively without ZZP). The neonatal admission rate was significantly higher in fetuses with the ZZP (8.7% in ZZP1 and 11.4% in ZZP2 versus 1.1% in controls). CONCLUSIONS: In line with previous research, our study suggest that SP is an almost nonexistent phenomenon. Alternatively, the ZigZag pattern (ZZP) has been defined as an exaggerated, irregular, "up and down" fluctuation of the baseline variability with an amplitude of >25 beats per min, lasting for 1 min or longer. It represents autonomic instability during human labor and it differs from the SP in terms of uniformity and length. Newborns with a ZZP during active maternal pushing were found to have statistically-significant lower Apgar scores at the 1st and 5th min, moderate and mild acidosis in the umbilical artery and an 8.7-11.4-fold higher neonatal admission rate. Clinicians should stop oxytocin infusion and/or active maternal pushing to improve fetal oxygenation if the ZZP is observed.

Fetal heart rate changes on the cardiotocograph trace secondary to maternal COVID-19 infection.

OBJECTIVE: To determine the cardiotocograph (CTG) changes in women with symptomatic COVID-19 infection. STUDY DESIGN: 12 anonymised CTG traces from 2 hospitals in Spain were retrospectively analysed by 2 independent assessors. CTG parameters were studied based on fetal pathophysiological responses to inflammation and hypoxia that would be expected based on the pathogenesis of COVID-19 patients. Correlation was made with perinatal outcomes (Apgar score at 5 min and umbilical cord pH). RESULTS: All fetuses showed an increased baseline FHR > 10 percent compared to the initial recording, in addition to absence of accelerations. 10 out of 12 CTG traces (83.3 percent) demonstrated late or prolonged decelerations and 7 out of 12 fetuses (58.3 percent) showed absence of cycling. Not a single case of sinusoidal pattern was observed. ZigZag pattern was found in 4 CTG traces (33 percent). Excessive uterine activity was observed in all CTG traces where uterine activity was monitored (10 out of 12). Apgar scores at 5 min were normal (>7) and absence of metabolic acidosis was found in the umbilical cord arterial pH (pH > 7.0) in the cases that were available (11 and 9, respectively). CONCLUSION: Fetuses of COVID-19 patients showed a raised baseline FHR (>10 percent), loss of accelerations, late decelerations, ZigZag pattern and absence of cycling probably due to the effects of maternal pyrexia, maternal inflammatory response and the "cytokine storm". However, the perinatal outcomes appear to be favourable. Therefore, healthcare providers should optimise the maternal environment first to rectify the reactive CTG changes instead of performing an urgent operative intervention.

Intraobserver and interobserver variability in first-trimester transvaginal ultrasound cervical length.

Objectives: To determine intraobserver and interobserver variability in the measurement of different cervical length (CL) components at the first trimester (endocervical canal and isthmus), describe the optimum measurement method (single line or two lines) and establish a normality curve of first trimester CL in our population.Methods: Women who attended the first-trimester US scan, between 11.0 and 13.6 weeks of gestation at Vall d'Hebron Universitary Hospital, Barcelona, Spain were included. Inclusion criteria were singleton pregnancies in women over 18 years of age, no gestational complications, uterine malformations or uterine surgery. Lengths of the endocervical canal and uterine isthmus were measured using two methods.Results: Both methods for endocervical canal measurement, single line and two lines, showed low intraobserver variability between examiners, with no statistical differences in the majority of measurements. A correct correlation existed between examiners using the single-line two-line measurements, with a concordance correlation coefficient of 0.76.Conclusions: Cervical length in the first trimester was reproducible for the same physician and between different physicians; however, it is essential to ensure examiners receive adequate training in the technique.