Clinical significance of fetal heart rate patterns during labor. IX: Prolonged pregnancy

A Review on the Vagus Nerve and Autonomic Nervous System During Fetal Development: Searching for Critical Windows

The autonomic nervous system (ANS) is one of the main biological systems that regulates the body's physiology. Autonomic nervous system regulatory capacity begins before birth as the sympathetic and parasympathetic activity contributes significantly to the fetus' development. In particular, several studies have shown how vagus nerve is involved in many vital processes during fetal, perinatal, and postnatal life: from the regulation of inflammation through the anti-inflammatory cholinergic pathway, which may affect the functioning of each organ, to the production of hormones involved in bioenergetic metabolism. In addition, the vagus nerve has been recognized as the primary afferent pathway capable of transmitting information to the brain from every organ of the body. Therefore, this hypothesis paper aims to review the development of ANS during fetal and perinatal life, focusing particularly on the vagus nerve, to identify possible "critical windows" that could impact its maturation. These "critical windows" could help clinicians know when to monitor fetuses to effectively assess the developmental status of both ANS and specifically the vagus nerve. In addition, this paper will focus on which factors-i.e., fetal characteristics and behaviors, maternal lifestyle and pathologies, placental health and dysfunction, labor, incubator conditions, and drug exposure-may have an impact on the development of the vagus during the above-mentioned "critical window" and how. This analysis could help clinicians and stakeholders define precise guidelines for improving the management of fetuses and newborns, particularly to reduce the potential adverse environmental impacts on ANS development that may lead to persistent long-term consequences. Since the development of ANS and the vagus influence have been shown to be reflected in cardiac variability, this paper will rely in particular on studies using fetal heart rate variability (fHRV) to monitor the continued growth and health of both animal and human fetuses. In fact, fHRV is a non-invasive marker whose changes have been associated with ANS development, vagal modulation, systemic and neurological inflammatory reactions, and even fetal distress during labor.

Umbilical cord blood gas analysis in augmented labour

Labour augmentation with oxytocin may produce an excessive increase in frequency, duration or strength in uterine contractions which may result in fetal stress. Umbilical cord acid-base assessment provides an objective parameter in evaluating the neonatal condition immediately after delivery. We evaluated the neonatal condition in 235 deliveries where oxytocin was used for labour augmentation. The umbilical cord blood acid-base status was correlated with intrapartum cardiotocographic findings and Apgar scores. In two cases we noted umbilical artery pH <7.05 but the BDecF was not higher than 11 mmol/l and the 5-minute Apgar score was 8 in all cases. Our results indicate that the use of oxytocin for labour augmentation had no adverse effects on neonatal condition.

Evaluation of non-reassuring fetal heart rate patterns with fetal pulse oximetry combined with vibratory acoustic stimulation

OBJECTIVE

To determine the value of fetal pulse oximetry and vibratory acoustic stimulation in the presence of non-reassuring fetal heart rate patterns during labor.

DESIGN

Prospective study in women monitored by cardiotocography and fetal pulse oximetry during labor.

MATERIALS AND METHODS

During a period of 18 months, 907 consecutive parturients in labor were monitored by cardiotocography. Out of these women, 63 were selected on the basis of a non-reassuring fetal heart rate tracing during the first stage of labor. In these cases, fetal pulse oximetry was applied. Vibratory acoustic stimulation was applied in fetuses without spontaneous reactivity in order to evaluate the fetal status.

RESULTS

Our cases were classified into three groups, according to the lower fetal oxygen saturation levels, from the time of oximetry application until delivery. Group A consisted of 29 cases where fetal oxygen saturation levels were > or = 41%, group B (20 cases) with fetal oxygen saturation of 31-40% and group C (14 cases) with levels of < 30%. Spontaneous reactivity was observed in 15 fetuses of group A and seven of group B, while no case of reactivity was noted in group C. Vibratory acoustic-induced reactivity was associated with low fetal oxygen saturation levels. The mean umbilical artery pH levels were 7.29 +/- 0.051 in group A, 7.21 +/- 0.057 in group B and 7.04 +/- 0.05 in group C.

CONCLUSION

Fetal pulse oximetry should be indicated not only in fetuses without any reactivity but also in those with induced reactivity, after the application of vibratory acoustic stimulation.

Fetal and uteroplacental circulatory changes in pregnancies proceeding beyond 43 weeks

BACKGROUND

Practically all reference curves for Doppler blood flow variables in pregnancy end at 40 weeks.

OBJECTIVE

To study fetal and uteroplacental circulatory changes in pregnancies proceeding beyond 43 weeks.

STUDY DESIGN

Longitudinal comparisons from 42 to 43 weeks and comparisons with controls at term.

MATERIAL

Thirty-four women delivered after 43 completed weeks (301 days) and a control group of 32 women delivered at 271 days of gestation.

METHODS

From 42 weeks (294 days), serial Doppler blood flow measurements were performed in the fetal descending aorta, umbilical vessels, and maternal uterine artery.

STATISTICAL METHODS

Student's unpaired t-test, Mann-Whitney U-test, and Fisher's exact test for comparison of groups; Student's paired t-test and Wilcoxon's signed-rank matched-pairs test for longitudinal data; simple linear regression analysis for comparison of variables. A two-tailed P-value of < 0.05 was considered statistically significant.

RESULTS

From 42 to 43 weeks, the mean flow velocity decreased significantly in the fetal aorta and increased significantly in the umbilical vein. Compared to controls, the velocity and volume flow in the aorta and the umbilical artery flow resistance were significantly lower at 43 weeks. No significant change in uterine artery flow resistance was found.

CONCLUSIONS

The changes in Doppler blood flow variables were all in accordance with physiological circulatory alterations enhancing continued fetal growth until the late post-term period. There were no signs of any general circulatory deterioration. Doppler velocimetry reference values at term may not be appropriate for evaluation of very advanced gestations.