The effect of uterine contractions on intrapartum fetal heart rate analyzed by a computerized system

Intrapartum uterine activity and neonatal outcomes: a systematic review

BACKGROUND

Increased uterine activity (UA) may not allow adequate recovery time for foetal oxygenation.

METHODS

The aim of the study was to determine if increased UA during labour is associated with an increased risk of either short- or long-term neurological injury in term neonates, or with neonatal proxy measures of intrapartum hypoxia-ischemia. MEDLINE, CINAHL, and ClinicalTrials.gov were searched using the following terms: uterine activity, excessive uterine activity, XSUA, uterine hyperstimulation, and tachysystole. Any study that analysed the relationship between UA during term labour and neurological outcomes/selected proxy neurological outcomes was eligible for inclusion. Outcomes from individual studies were reported in tables and presented descriptively with odds ratios (OR) and 95% confidence intervals (CI) for dichotomous outcomes and means with standard deviations for continuous outcomes. Where group numbers were provided, ORs and their CIs were calculated according to Altman.

MAIN RESULTS

Twelve studies met the inclusion criteria. Seven studies featured umbilical artery pH as an individual outcome. Umbilical artery base excess and Apgar scores were both reported as individual outcomes in four studies. No study examined long term neurodevelopmental outcomes and only one study reported on encephalopathy as an outcome. The evidence for a relationship between UA and adverse infant outcomes was inconsistent. The reported estimated effect size varied from non-existent to clinically significant.

CONCLUSIONS

There is some evidence that increased UA may be a non-specific predictor of depressed neurological function in the newborn, but it is inconsistent and insufficient to support the conclusion that an association generally exists.

Effect of uterine contraction and amniotomy on fetal cardiotocograph

Both uterine contractions and artificial rupture of fetal membranes (amniotomy) are important events during delivery phase, this study was planned to determine possible effects of both events on fetal heart rate using nonstress test method. Sixty term pregnant women admitted for termination of pregnancy were selected. Primary nonstress test was performed, then nonstress test was done after active uterine contractions. After the amniotomy the last test was done. All results were statistically analyzed. Out of 60 term pregnant women, 51 (85%) patients reported acceleration for primary nonstress test. After uterine contractions, acceleration was seen in 46 (76.7%) patients, this happened in 40 (66.7%) cases after amniotomy. There was no deceleration after primary nonstress test. However, deceleration reported after uterine contractions and amniotomy in five (8.3%) and two (3.3%) cases, respectively. The 56 (93.3%) patients showed variability in primary nonstress test; variability following the uterine contractions and amniotomy was seen in 58 (96.7%) and 56 (93.3%) of subjects, respectively. None of them were statistically significant (p > 0.05). Mean fetal heart rate baseline in primary Nonstress test was (141.00 +/- 9.35), this was (140.50 +/-10.51) following uterine contractions and (143.08 +/- 11.97) after amniotomy. Baseline fetal heart rate reduction, statistically significant, was seen following uterine contractions (r = +0.28, p = 0.02). This means reductions in lower baseline fetal heart rates will be more outstanding. Uterine contractions and amniotomy had no correlation with presence or absence of variability, acceleration and deceleration.

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.

Foetal heart rate power spectrum response to uterine contraction

Cardiotocography is the most diffused prenatal diagnostic technique in clinical routine. The simultaneous recording of foetal heart rate (FHR) and uterine contractions (UC) provides useful information about foetal well-being during pregnancy and labour. However, foetal electronic monitoring interpretation still lacks reproducibility and objectivity. New methods of interpretation and new parameters can further support physicians' decisions. Besides common time-domain analysis, study of the variability of FHR can potentially reveal autonomic nervous system activity of the foetus. In particular, it is clinically relevant to investigate foetal reactions to UC to diagnose foetal distress early. Uterine contraction being a strong stimulus for the foetus and its autonomic nervous system, it is worth exploring the FHR variability response. This study aims to analyse modifications of the power spectrum of FHR variability corresponding to UC. Cardiotocographic signal tracts corresponding to 127 UC relative to 30 healthy foetuses were analysed. Results mainly show a general, statistically significant (t test, p<0.01) power increase of the FHR variability in the LF 0.03-0.2 Hz and HF 0.2-1 in correspondence of the contraction with respect to a reference tract set before contraction onset. Time evolution of the power within these bands was computed by means of time-varying spectral estimation to concisely show the FHR response along a uterine contraction. A synchronised grand average of these responses was also computed to verify repeatability, using the contraction apex as time reference. Such modifications of the foetal HRV that follow a contraction can be a sign of ANS reaction and, therefore, additional, objective information about foetal reactivity during labour.

Periodic spectral components of fetal heart rate variability reflect the changes in cord arterial base deficit values: a preliminary report

Fetal distress changes the function of the autonomic nervous system. These changes are reflected in the fetal heart rate and can be quantified with power spectrum analysis of heart rate variability. The purpose of this study was to find out whether spectral components of fetal heart rate variability (FHRV) during labor are associated with fetal cord arterial base deficit values at birth. The association between FHRV and umbilical cord arterial base deficit was studied in 14 singleton fetuses with normal pregnancy at 35-40 weeks of gestation. Fetal ECG was recorded by scalp-electrode using a STAN Fetal ECG monitor (Cinventa Ab, Mölndal, Sweden). FHRV was quantified by computing Fast-Fourier-transformed heart rate (HR) spectra at three frequency bands: low-frequency (LF) 0.03-0.07 Hz, mid-frequency (MF) 0.07-0.13 Hz and high-frequency (HF) 0.13-1.0 Hz. We found that total FHRV and MF FHRV were lower in fetuses with cord arterial base deficit 8 to 12 mmol/L in comparison to the fetuses with normal cord arterial base deficit value (P=0.02 and P=0.01, respectively). A linear correlation was found between the spectral densities and the cord arterial base deficit values (r=0.4 and r=0.6, respectively). We conclude that the results suggest changes in the autonomic nervous cardiac control in fetuses with cord arterial base deficit between 8 to 12 mmol/L. The clinical applicability of our observations on FHRV in predicting fetal distress remains to be further studied.

Computer analysis of the fetal heart rate

Computer analysis of the fetal heart rate is a technology of the Information Age commercially available for research and clinical practice. Intelligent systems are engineered with algorithms or neural networks designed to simulate expert knowledge. Automated analysis has provided objective, standardized, and reproducible data used to research fetal heart rate responses in the antepartum and intrapartum setting. Perinatal information systems can integrate FHR analysis and data management.

New developments in fetal monitoring for the anesthesiologist

Assessing fetal wellbeing has evolved from the ancient awareness of 'quickening' to a vast array of biophysical, imaging and biochemical methods. Because the results of these tests influence the urgency of fetal delivery and sometimes the choice of maternal anesthetic technique, it is important for anesthesiologists to understand the fundamentals of fetal monitoring and the changing face of new developments in this field. Noteworthy publications from the past year on this topic include new guidelines for the interpretation of fetal heart monitoring, advances in intrapartum fetal pulse oximetry, thresholds of acidosis associated with fetal injury, and efforts to decrease cerebral palsy through better antenatal biophysical testing.