The effect of variable heart rate decelerations on intraventricular hemorrhage and other perinatal outcomes in preterm infants

Increased fetal heart rate variability in periventricular leukomalacia

OBJECTIVE

This study used quantitative analysis to determine whether increased variability in fetal heart rate (FHR) is related to the risk of developing periventricular leukomalacia (PVL).

METHODS

We analyzed 124 FHR traces of neonates delivered preterm at 27-33 weeks' gestation to 105 mothers. FHR traces 1-3h before delivery were translated into power-spectrum curves using a fast Fourier transformation. The total power (the area under the curve of 1-10 cycles per minute), segmental power of every cycle per minute, peak power, and frequency edges were calculated, and their relationship with the subsequent development of PVL was examined.

RESULTS

Total power was significantly higher in the PVL group (n=9, median 1813, range 1064-2426) compared to the non-PVL group (n=114, median 1383, range 381-3324, p=0.029). Infants in the PVL group had greater segmental power in segments with 1-2, 2-3, and 9-10 cycles per minute, than those in the non-PVL group. Total power of ⩾1550 was significantly correlated with the subsequent development of PVL and premature rupture of membranes. Furthermore, the frequency of pregnancy-induced hypertension was significantly reduced in the fetuses with a total power of ⩾1550.

CONCLUSION

Our study suggests that a fetus with increased FHR variability is at risk of developing PVL. This study provides additional evidence supporting the contribution of antenatal factors to the subsequent development of PVL.

Electronic fetal heart rate monitoring and its relationship to neonatal and infant mortality in the United States

OBJECTIVE

To examine the association between electronic fetal heart rate monitoring and neonatal and infant mortality, as well as neonatal morbidity.

STUDY DESIGN

We used the United States 2004 linked birth and infant death data. Multivariable log-binomial regression models were fitted to estimate risk ratio for association between electronic fetal heart rate monitoring and mortality, while adjusting for potential confounders.

RESULTS

In 2004, 89% of singleton pregnancies had electronic fetal heart rate monitoring. Electronic fetal heart rate monitoring was associated with significantly lower infant mortality (adjusted relative risk, 0.75); this was mainly driven by the lower risk of early neonatal mortality (adjusted relative risk, 0.50). In low-risk pregnancies, electronic fetal heart rate monitoring was associated with decreased risk for Apgar scores <4 at 5 minutes (relative risk, 0.54); in high-risk pregnancies, with decreased risk of neonatal seizures (relative risk, 0.65).

CONCLUSION

In the United States, the use of electronic fetal heart rate monitoring was associated with a substantial decrease in early neonatal mortality and morbidity that lowered infant mortality.

Using malpractice claims to identify risk factors for neurological impairment among infants following non-reassuring fetal heart rate patterns during labour

RATIONALE, AIMS AND OBJECTIVES

We sought to use a novel case-selection methodology to identify antenatal or intrapartum risk factors associated with neonatal neurological impairment following non-reassuring fetal heart rate patterns during labour.

METHOD

We used a retrospective case-control design with bivariate and multivariate conditional logistic regression. Cases were births in which electronic fetal monitoring (EFM) showed non-reassuring patterns and the infant had neurological disability. Controls were births in which EFM was non-reassuring but the infant was born healthy. We identified 36 cases from among malpractice claims filed with a liability insurer in Massachusetts between 1985 and 2001 and randomly selected 70 controls, matching them to cases by hospital, birth date and gestational age.

RESULTS

More cases had maternal antenatal vaginal bleeding (P = 0.004), a prolonged latent phase or protracted dilation during the first stage of labour (P = 0.03), and protracted descent or prolonged second stage (P = 0.01). More cases also had minimal variability on EFM on admission (P = 0.02) and during the second stage (P = 0.02). Multivariate analysis highlighted three significant predictors of neurological injury following complicated labour: antenatal vaginal bleeding (OR = 27.1), prolonged latent phase or protracted dilation in the first stage (OR = 4.0) and EFM showing minimal variability in the first stage (OR = 4.3).

CONCLUSION

These promising initial findings suggest that future research into outcomes from complicated labour with non-reassuring heart rate patterns should focus on maternal history of vaginal bleeding, slow labour and minimal variability on EFM.

Fetal brain sonography and fetal heart rate patterns in the preterm fetus

OBJECTIVE

The objective of the study was to study whether peri- and intraventricular echodensities in the brain of fetuses at risk for preterm birth are associated with changes in fetal heart rate (FHR) parameters.

STUDY DESIGN

Twenty preterm fetuses with peri- and intraventricular echodensities detected by transvaginal ultrasonography were matched with 20 fetuses without echodensities for gestational age, growth parameters, clinical disease, and maternal medication. Baseline FHR, long- and short-term variability, and the presence of accelerations and decelerations were analyzed with a computerized system and compared with the Wilcoxon matched-pairs signed-rank test. Both cases and controls were compared with a normal population.

RESULTS

No statistical differences in FHR parameters were found between cases with and controls without peri- and intraventricular echodensities. Both cases and controls had lower long- and short-term variabilities than the normal population.

CONCLUSION

No association between the presence of peri- and intraventricular echodensities and specific FHR changes was demonstrated.

[Fetal heart rate during labour: definitions and interpretation]

Continuous fetal heart rate monitoring is widely used during labor even in low risk pregnancies. Consensus is necessary to define and interpret accurately the different FHR patterns. The normal FHR tracing include baseline rate between 110-160 beats per minute (bpm), moderate variability (6-25 bpm), presence of accelerations and no decelerations. Uterine activity is monitored simultaneously: contractions frequency, duration, amplitude and relaxation time must be also normal. Abnormal baseline heart rate during 10 minutes or more is termed tachycardia above 160 bpm (except for FIGO above 150) and bradycardia below 110 bpm. Variability is minimal below 6 bpm and absent when non visible. Decelerations are classified as early, variable, late, and prolonged. Early and late decelerations have an onset gradual decrease of FHR, in contrast variable decelerations have an abrupt onset. Early deceleration is coincident in timing with uterine contraction. Variable deceleration is variable in onset, duration and timing, and may be described as typical or non reassuring. Late deceleration is associated with uterine contraction; the onset, nadir, and recovery occur after onset, peak and end of the contraction. Prolonged deceleration is lasting more than two but less 10 minutes, with almost onset abrupt and no repetition. Electronic fetal monitoring is a method to detect risk of fetal asphyxia; analysis and interpretation of FHR patterns are difficult with a high false positive rate, increasing operative deliveries. The patterns who are predictive of severe fetal acidosis include recurrent late or variable or prolonged decelerations or bradycardia, with absent FHR variability, and sudden severe bradycardia. The other FHR patterns are not conclusive and defined as non reassuring; obstetrical risk factors must be considered and other method (like scalp sampling for pH) utilised to evaluate fetal state.

Fetal hypoxic and ischemic injuries

PURPOSE OF REVIEW

The principles of neonatal neurological protection following intrapartum hypoxia are briefly reviewed. The physiological principles behind the use of cardiotocograph patterns in defining the timing and mechanism of fetal hypoxia and injury are then demonstrated.

RECENT FINDINGS

Fetal neurological injury may result from progressive hypoxemia, acidosis, diminished cardiac output and cerebral ischemia, manifested at birth as low Apgar scores, multisystem compromise, severe acidosis and encephalopathy. More commonly, however, intrapartum injury results from often intermittent, regional ischemia secondary to umbilical cord or head compression resulting in hemorrhage or infarction. Under these circumstances, the amount of umbilical acidosis and neonatal encephalopathy varies and the potential candidate for neuroprotection may escape recognition and timely treatment. Selecting infants likely to benefit from neuroprotection requires information on the timing, duration and mechanism of hypoxia. Neonatal parameters, including low Apgar scores, acidosis, even seizures, lack sensitivity and specificity. Cardiotocograph patterns are capable of determining the duration, mechanism and severity of hypoxia and occasionally, the timing of neurological injury.

SUMMARY

Protecting the newborn from the neurological consequences of intrapartum hypoxia requires critical definition of the mechanism and timing of this exposure. cardiotocograph tracings offer the opportunity to refine the selection of candidates for neonatal rescue.