The physiology of fetal heart rate patterns and perinatal asphyxia

Increased variability of fetal heart rate during labour: a review of preclinical and clinical studies

Increased fetal heart rate variability (FHRV) in intrapartum cardiotocographic recording has been variably defined and poorly understood, limiting its clinical utility. Both preclinical (animal) and clinical (human) evidence support that increased FHRV is observed in the early stage of intrapartum fetal hypoxaemia but can also be observed in a subset of fetuses during the preterminal stage of repeated hypoxaemia. This review of available evidence provides data and expert opinion on the pathophysiology of increased FHRV, its clinical significance and a stepwise approach regarding the management of this pattern, and propose recommendations for standardisation of related terminology.

No. 396-Fetal Health Surveillance: Intrapartum Consensus Guideline

OBJECTIVE

To present evidence and recommendations regarding use, classification, interpretation, response, and documentation of fetal surveillance in the intrapartum period and to provide information to help minimize the risk of birth asphyxia while maintaining the lowest possible rate of obstetrical intervention.

INTENDED USERS

Members of intrapartum care teams, including but not limited to obstetricians, family physicians, midwives and nurses, and their learners TARGET POPULATION: Intrapartum women OPTIONS: All methods of uterine activity assessment and fetal heart rate surveillance were considered in developing this document.

OUTCOMES

The impact, benefits, and risks of different methods of surveillance on the diverse maternal-fetal health conditions have been reviewed based on current evidence and expert opinion. No fetal surveillance method will provide 100% detection of fetal compromise; thus, all FHS methods are viewed as screening tests. As the evidence continues to evolve, caregivers from all disciplines are encouraged to attend evidence-based Canadian educational programs every 2 years.

EVIDENCE

Literature published between January 1976 and February 2019 was reviewed. Medline, the Cochrane Database, and international guidelines were used to search the literature for all studies on intrapartum fetal surveillance.

VALIDATION METHODS

The principal and contributing authors agreed to the content and recommendations. The Board of the Society of Obstetricians and Gynaecologists of Canada approved the final draft for publication. The level of evidence has been determined using the criteria and classifications of the Canadian Task Force on Preventive Health Care.

BENEFITS, HARM, AND COSTS

Consistent interdisciplinary use of the guideline, appropriate equipment, and trained professional staff enhances safe intrapartum care. Women and their support person(s) should be informed of the benefits and harms of different methods of fetal health surveillance.

RECOMMENDATIONS

CommunicationSupport During Active LabourPrinciples of Intrapartum Fetal SurveillanceSelecting the Method of Fetal Heart Rate Monitoring: Intermittent Auscultation or Electronic Fetal MonitoringPaper SpeedAdmission AssessmentsEpidural AnalgesiaIntermittent Auscultation in LabourElectronic Fetal Monitoring in LabourClassification of Intrapartum Fetal SurveillanceMaternal Heart RateFetal Health Surveillance Assessment in the Active Second Stage of LabourIntrauterine ResuscitationDigital Fetal Scalp StimulationFetal Scalp Blood SamplingUmbilical Cord Blood GasesDocumentationFetal Surveillance Technology Not RecommendedFetal Health Surveillance Education.

Clinical Implications of Fetal Heart Rate Interpretation Based on Underlying Physiology

Understanding the physiology of fetal oxygenation and various influences on fetal heart rate control supports nurses, midwives, and physicians in interpreting and managing electronic fetal heart rate tracings during labor and birth. Maternal oxygenation, placental circulation and exchange, umbilical blood flow and fetal circulation affect fetal oxygenation, which is reflected in observed fetal heart rate patterns. Fetal heart control is further influenced by the central and autonomic nervous systems, baroreceptors, chemoreceptors, humoral factors, sleep-wake patterns, breathing movements, medications, painful stimuli, sound and vibrations, and temperature. Knowledge of the physiologic basis for fetal heart rate pattern characteristics guides interventions to improve fetal oxygenation when indicated. A review and update on clinical implications of fetal heart rate pattern interpretation based on underlying physiology is presented.

Delphi consensus statement on intrapartum fetal monitoring in low-resource settings

OBJECTIVE

To determine acceptable and achievable strategies of intrapartum fetal monitoring in busy low-resource settings.

METHODS

Three rounds of online Delphi surveys were conducted between January 1 and October 31, 2017. International experts with experience in low-resource settings scored the importance of intrapartum fetal monitoring methods.

RESULTS

71 experts completed all three rounds (28 midwives, 43 obstetricians). Consensus was reached on (1) need for an admission test, (2) handheld Doppler for intrapartum fetal monitoring, (3) intermittent auscultation (IA) every 30 minutes for low-risk pregnancies during the first stage of labor and after every contraction for high-risk pregnancies in the second stage, (4) contraction monitoring hourly for low-risk pregnancies in the first stage, and (5) adjunctive tests. Consensus was not reached on frequency of IA or contraction monitoring for high-risk women in the first stage or low-risk women in the second stage of labor.

CONCLUSION

There is a gap between international recommendations and what is physically possible in many labor wards in low-resource settings. Research on how to effectively implement the consensus on fetal assessment at admission and use of handheld Doppler during labor and delivery is crucial to support staff in achieving the best possible care in low-resource settings.

Plasticity in the Neonatal Brain following Hypoxic-Ischaemic Injury

Hypoxic-ischaemic damage to the developing brain is a leading cause of child death, with high mortality and morbidity, including cerebral palsy, epilepsy, and cognitive disabilities. The developmental stage of the brain and the severity of the insult influence the selective regional vulnerability and the subsequent clinical manifestations. The increased susceptibility to hypoxia-ischaemia (HI) of periventricular white matter in preterm infants predisposes the immature brain to motor, cognitive, and sensory deficits, with cognitive impairment associated with earlier gestational age. In term infants HI causes selective damage to sensorimotor cortex, basal ganglia, thalamus, and brain stem. Even though the immature brain is more malleable to external stimuli compared to the adult one, a hypoxic-ischaemic event to the neonate interrupts the shaping of central motor pathways and can affect normal developmental plasticity through altering neurotransmission, changes in cellular signalling, neural connectivity and function, wrong targeted innervation, and interruption of developmental apoptosis. Models of neonatal HI demonstrate three morphologically different types of cell death, that is, apoptosis, necrosis, and autophagy, which crosstalk and can exist as a continuum in the same cell. In the present review we discuss the mechanisms of HI injury to the immature brain and the way they affect plasticity.

Sex differences in linear and complex fetal heart rate dynamics of normal and acidemic fetuses in the minutes preceding delivery

AIM

To assess linear and complex heart rate dynamics in relation to fetal gender in normal and acidemic fetuses during the minutes preceding delivery.

METHODS

Linear and non-linear fetal heart rate indices, namely mean FHR, long-term irregularity index, short-term variability, low and high frequency spectral indices, approximate and sample entropy, were assessed in 36 female and 30 male fetuses, adjusted for gestational age and weight, during the minutes preceding delivery. Analysis was performed in the initial and final minutes of each tracing in fetuses with umbilical artery blood pH at delivery >or=7.20, 7.11-7.19 and <or=7.10.

RESULTS

Progression of labor was associated with a significant decrease in non-linear indices and an increase in almost all linear indices, both in female and male fetuses, but changes were more marked in female fetuses. Non-acidemic females showed higher mean FHR in the final minutes of labor, compared with males. Acidemic females had higher linear indices when compared to similar male fetuses.

CONCLUSIONS

During the minutes preceding delivery, female fetuses express higher linear indices than male fetuses, suggesting greater activation of the autonomic nervous system, while maintaining similar complexity indices, which suggests different reaction and adaptation capabilities to stress and distress.

Uterine activity: implications for the condition of the fetus

AIM

The aim of this review is to provide more insight in the fetal mechanisms as a response to uterine contractions and to emphasize the importance of correct assessment of uterine activity (UA) patterns during labor.

STUDY RESULTS

UA causes a decreased flow through the uterine artery. In the healthy uncompromised fetus, this will not cause fetal acidemia. The fetus has developed certain protection mechanisms to survive labor; (1) During a contraction, fetal preload increases and enables the fetus to maintain a constant blood flow through the umbilical artery and (2) UA increases the blood flow in the fetal middle cerebral artery, i.e., a brain sparing effect. The shortcoming of those protection mechanisms in the compromised fetus and in case of excessive UA increases the risk of adverse fetal outcome. The brain sparing effect will become more pronounced to compensate for the decreased umbilical artery blood flow and fetal oxygen saturation. Maintenance of normal UA, especially a sufficiently long relaxation time, is essential so that the supply of well oxygenated maternal blood to the intervillous space will be restored and the fetal cerebral oxygen saturation can remain stable.

CONCLUSION

Adequate UA monitoring is a prerequisite for proper reading and interpretation of cardiotocograms. It alarms in cases of excessive UA and can help to prevent fetal acidemia. Uterine contraction monitoring deserves full attention in daily obstetric practice.

Linear and nonlinear fetal heart rate analysis of normal and acidemic fetuses in the minutes preceding delivery

Linear and nonlinear fetal heart rate (FHR) indices, namely mean FHR, interval index (II), very low, low and high frequencies, approximate (ApEn) and sample entropy (SampEn), were computed, immediately before delivery, in the initial and final FHR tracing segments, from 48 normal, 10 mildly acidemic and 10 moderate-to-severely acidemic fetuses. Progression of labor was associated with a significant increase in linear frequency domain indices whereas nonlinear indices were significantly decreased. Moderate-to-severe fetal acidemia was associated with a significant decrease in nonlinear indices. The best discrimination between moderate-to-severe acidemic fetuses and the remaining cases was obtained combining II and ApEn(2,0.15), with a specificity of 71% and a sensitivity of 80%. These findings support the hypothesis of increased autonomic nervous system activity in the final minutes of labor and of decreased central nervous system activity, both in the final minutes of labor and in moderate-to-severe acidemic fetuses.

Fetal assessment in the adult intensive care unit

Ideally the clinical management of a critically ill pregnant woman is based on a collaborative approach with members of the ICU and perinatal team each contributing their expertise to promote the best out-come for the mother and baby. The interdisciplinary team also should include anesthesia providers and neonatal specialists. The physical space (ICU or labor and delivery unit) is less important than the quality and coordination of the care and treatment. The responsibility for fetal assessment when the woman is critically ill should rest with those who have this expertise. Working together provides the best opportunity for optimal outcomes.