Braxton Hicks' contractions and motor behavior in the near-term human fetus

Approaches to Preventing Intrapartum Fetal Injury

Electronic fetal monitoring (EFM) was introduced into obstetric practice in 1970 as a test to identify early deterioration of fetal acid-base balance in the expectation that prompt intervention ("rescue") would reduce neonatal morbidity and mortality. Clinical trials using a variety of visual or computer-based classifications and algorithms for intervention have failed repeatedly to demonstrate improved immediate or long-term outcomes with this technique, which has, however, contributed to an increased rate of operative deliveries (deemed "unnecessary"). In this review, we discuss the limitations of current classifications of FHR patterns and management guidelines based on them. We argue that these clinical and computer-based formulations pay too much attention to the detection of systemic fetal acidosis/hypoxia and too little attention not only to the pathophysiology of FHR patterns but to the provenance of fetal neurological injury and to the relationship of intrapartum injury to the condition of the newborn. Although they do not reliably predict fetal acidosis, FHR patterns, properly interpreted in the context of the clinical circumstances, do reliably identify fetal neurological integrity (behavior) and are a biomarker of fetal neurological injury (separate from asphyxia). They provide insight into the mechanisms and trajectory (evolution) of any hypoxic or ischemic threat to the fetus and have particular promise in signaling preventive measures (1) to enhance the outcome, (2) to reduce the frequency of "abnormal" FHR patterns that require urgent intervention, and (3) to inform the decision to provide neuroprotection to the newborn.

Uterine contractions clustering based on electrohysterography

The uterine electromyogram, also named Electrohysterogram (EHG), is a non-invasive technique that has been used for pregnancy and labour monitoring as well as for research work on uterine physiology. This technique is well established in this field. There is however a vast unexplored potential in the EHG that is currently the subject of interdisciplinary research work involving different scientific fields such as medicine, engineering, physics and mathematics. In this paper, an unsupervised clustering method is applied to a previously obtained set of frequency spectral representations of the respective EHG signal contractions that were previously automatically detected and delineated. An innovative approach using the complete spectrum projection is described, rather than a set of relevant points. The feasibility of the method is established despite the concerns of possible computational burden incurred by the processing of the whole spectrum. Given the unsupervised nature of this classification, a validation procedure was performed whereas the obtained clusters were labelled through the correlation with the common knowledge about the most relevant uterine contraction types, as described in the literature. As a result of this study, a spectral description of the Alvarez contractions was obtained where it was possible to breakdown these important events in two different types according to their spectrum. Spectral estimates of Braxton-Hicks contractions were also obtained and associated to one of the clusters. This led to a full spectral characterization of these uterine events.

Normal fetal motility: an overview

After 35 years of real-time two-dimensional sonography, and now that 4D sonography is within our grasp, this article presents an overview of present-day knowledge of normal fetal motility. A literature search was carried out on articles from 1970, using the keywords: 'fetal', 'movements', 'motility', 'movement patterns', 'ultrasound' and 'sonography'. Inclusion criteria were human studies and use of real-time sonography. Articles were screened for type of motor assessment procedure, in terms of whether they: specified movements for participating body parts (specific movement pattern, SMP), were qualitative (performance in terms of speed and amplitude), were quantitative, identified behavioral states, stated the duration of observation, and specified gestational age. We noted developmental milestones obtained for each study aim. One of four aims was identified for each article, depending on whether it focused on emergence, development, or continuity after birth of the movement patterns, or on the relationship of various motor aspects to other parameters that evaluate fetal condition, such as blood flow and fetal heart rate. A total of 109 relevant articles was identified, examining 9862 fetuses. Assessment was performed primarily with analysis of SMPs (89%); 52% also included non-SMPs (NSMPs), 78% included quantification, 24% assessment of quality, and 32% behavioral states. The duration of observation was 1 h or longer in 50% of the studies. The focus in 28 studies was on emergence, in 44 it was on development, in five it was on continuity and in 32 it was on relationship of the movements with other parameters of fetal well-being. A few milestones identified were determination of the strictly age-related emergence of SMPs and behavioral states, the highly reproducible quality of SMPs throughout gestation, the age-related trends in quantified SMPs, the continuity in quality and quantity after birth, and the close relationship between motility and heart-rate variability, flow parameters, and behavioral states. Periods of longest inactivity recorded before 20 weeks were 13 min; after 30 weeks they were 45 min. Much insight was obtained into the development of motility and its relationship to other parameters from those articles applying comparable assessment procedures. An assessment procedure with well-defined SMPs, qualitative and quantitative aspects of SMPs and NSMPs, and an observation period dependent on age are advocated for future research.

Prenatal stress and risk for psychopathology: specific effects or induction of general susceptibility?

This review focuses on prenatal stress as a risk factor for psychopathology. Evidence from animal studies is summarized, and the relevance of prenatal stress models in animals for human studies is discussed. In the offspring of prenatally stressed animals, overactivity and impaired negative feedback regulation of the hypothalamic-pituitary-adrenal axis are consistent findings and may reflect a pathophysiological mechanism involved in the development of psychopathology. Reduced activity of the opioid GABA/benzodiazepine, serotonin, and dopamine systems and increased activity of the sympathico-adrenal system have been found as well. These alterations have been linked to a diverse spectrum of psychopathology. Therefore, the evidence supports the view that exposure to prenatal stress may result in a general susceptibility to psychopathology, rather than exerting a direct effect on a specific form of psychopathology.

Late-onset fetal cardiac decelerations associated with fetal breathing movements

BACKGROUND

While late decelerations are regarded as signs of fetal hypoxemia, fetal breathing movements (FBM) associated with late decelerations invariably have normal outcomes. Could late decelerations sometimes represent FBM?

MATERIALS AND METHODS

Six patients between 37 and 42 weeks' gestation with 'late decelerations' associated with FBM (by ultrasound or tocodynamometer) during ante- or intrapartum monitoring were evaluated. Three were at high risk (diabetes, postdates, intrauterine growth restriction) and three were at low-risk.

RESULTS

'Late decelerations' arose in previously reassuring tracings. Oxygen or positional change had no effect. The decelerations were variable in length and shallow, and contained increased variability. Normal baseline rate and variability were maintained after the deceleration. Neonatal outcomes were normal.

CONCLUSION

'Late decelerations' as described are associated with normal outcome and may represent FBM. This understanding may reduce unnecessary interventions.

The effects of maternal exercise on fetal heart rate and movement patterns

The aim of this study was to investigate the effects of maternal exercise on fetal movement and heart rate patterns. Twelve healthy women at 29-32 weeks of pregnancy performed a (sub)maximal bicycle exercise test, reaching 53-99% (median 82%) of their maximal increase in heart rate (MIHR). Fetal heart rate (FHR) and its variation and fetal body and breathing movements were recorded for 1 h before and after the exercise and also on a control day. After exercise, FHR was higher for 30 min and FHR variation reduced for 20 min as compared with pre-exercise levels (P < 0.01). Fetal body movements were reduced for the first 5 min following exercise (P < 0.05). In two cases, fetal bradycardia was observed (at 89 and 99% MIHR) followed by a considerable reduction in FHR variation and absence of body and breathing movements for 20 min. In the other 10 fetuses fetal breathing activity was increased for the first 5 min after exercise (P < 0.05). FHR (and to a lesser extent breathing movements) increased with increasing level of maternal exercise, but decreased when the % MIHR exceeded approximately 90%. Body movements were negatively correlated with the % MIHR (P < 0.05). In conclusion, moderate to heavy maternal exercise clearly affects the human fetus with signs of transient fetal impairment after heavy exercise.

Contractile activity of the uterus prior to labor alters the temporal organization of spontaneous motor activity in the fetal sheep

Contractile activity of the uterus before the onset of labor (uterine contractures) has been described in a number of species and provides a powerful source of repeated stimulation for the fetus throughout much of gestation. To understand how fetal behavior responds to this dynamic aspect of the intrauterine environment, we investigated the effects of uterine contractures on the temporal organization of spontaneous motor activity in the fetal sheep during the last fifth of gestation. Eleven fetuses were instrumented on 113-116 days of gestation (dGA). Electromyogram (EMG) activity was recorded from flexor and extensor muscles in the fetal forelimbs and hindlimbs, and from the uterus. Pooled limb EMG activity from 2300 hr to 0700 hr on 118, 125, 132, and 139 dGA before, during, and after uterine contractures was spectral analyzed to detect and quantify the cyclic organization in fetal motor activity. There was strong evidence of cyclic organization in fetal motor activity (CM) at each gestational age, similar to what has been described in the fetal rat and human. There was no evidence of developmental changes in the baseline spectral measures of CM. The most prominent feature of the response of CM to uterine contractures was a transient decrease in irregularity at 118-132 dGA. The strength of CM increased during contractures at 125 and 132 dGA, and a slight acceleration of CM during contractures was detected at 118 and 139 dGA. The results demonstrate that the stimulation associated with contractures influences an important source of complexity in early behavioral organization. The results are consistent with speculation by others that uterine contractures might induce transient cerebral hypoxemia in the fetus, and suggest that conditions established in the first few minutes of sustained uterine activity constitute the effective perturbation of CM.

Fetal breathing movements in late diabetic pregnancy: relationship to fetal heart rate patterns and Braxton Hicks' contractions

In type-1 diabetic pregnancy, the occurrence of fetal breathing movements (FBM) was studied in relation to the fetal heart rate patterns (HRPs) A and B and to Braxton Hicks' contractions. Simultaneous 2-h recordings of fetal heart rate and body, eye and breathing movements were available for analysis (n = 44). These recordings were made in 20 fetuses of diabetic women at 32-38 weeks of gestation. Uterine activity was monitored at 36 and 38 weeks. For all recordings combined, the median incidences of FBM during HRPs A and B were 23% and 41%, respectively (NS). At low overall breathing activity (< 50% of total observation time), FBM were more numerous during HRP B than during HRP A in 83% of the recordings. However, if the overall breathing activity exceeded 50% of time FBM were preferentially made during HRP A in 93% of the recordings. This relationship was most pronounced at 38 weeks. These results corroborate our previous findings in the healthy near-term fetus. They show even more clearly that the state-dependent occurrence of FBM depends on the fetus' drive to breathe. During the recordings, breathing activity remained unchanged at all gestational ages studied, in contrast to the gradual decline in FBM seen in normal pregnancy. Braxton Hicks's contractions had no effect on FBM, which differs from the specific distribution of FBM during uterine contractions as previously found in uncomplicated pregnancies. We conclude that FBM in late diabetic pregnancy are not influenced by Braxton Hicks' contractions and that they do not show a clear-cut state-dependency. The (neural) mechanism underlying FBM differs from that in normal pregnancy.

Feasibility of continuous recording of fetal heart rate in the near term bovine fetus by means of transabdominal Doppler

A transabdominal Doppler technique for the recording of fetal heart rate (FHR) was investigated in the bovine fetus. During the last 2 weeks of gestation recordings were made once or twice per week in eight cows by placing a 1.5 MHz Doppler transducer on the right ventral abdominal wall. Continuous FHR recordings with a duration of more than 30 min were obtained in 29 of the 35 sessions. Major displacements of the fetus were the main cause of recording failure. The overall mean baseline FHR was 105 +/- 1.5 bpm with a range of 90 to 125 bpm. The mean bandwidth of the baseline FHR was 10.8 +/- 0.7 bpm with a range of < 5 to 20 bpm. Periods with different bandwidths alternated. The alternation of bovine FHR patterns pointed to the existence of different fetal behavioural states. The mean number of accelerations of FHR was 7.1 +/- 1.0 per hour. Many of the accelerations coincided with visible or perceptible fetal body movements. Decelerations of FHR occurred less frequently (range 0 to 4 per h). A period of tachycardia accompanied by an increased number of fetal movements occurred in 3 of the 29 FHR recordings. This non-invasive technique appears to be suitable to study FHR patterns during gestation and to investigate the presence and characteristics of behavioural states in the bovine fetus. It also provides the possibility to study effects on the fetus of drugs administered to the dam.

Patterns of breathing movements in the near-term human fetus: relationship to behavioural states

The occurrence of fetal breathing movements was studied in relation to fetal behavioural states 1F and 2F, as recognized by the heart rate patterns A and B, respectively. Simultaneous recordings of fetal heart rate and body, eye and breathing movements were available for analysis (n = 88). These recordings, lasting > or = 2 h, had been made in healthy near-term fetuses during the afternoon or evening, starting about 1 h after the maternal meal. In the majority of recordings fetal breathing activity was lower during heart rate pattern A than during pattern B, but as the opposite occurred in 29/88 recordings (33%), the interstate difference was not significant (P = 0.052). Detailed analysis revealed that breathing movements were more numerous during pattern B than during pattern A if the incidence of breathing during a particular time period was low (30-40% of time). At a high overall breathing incidence (> 40%), however, breathing movements were more often present during pattern A than during pattern B. The latter occurred especially in the first hour of recording, i.e. less distant in time from maternal meals. We conclude that fetal breathing activity is generally higher during state 2F than during state 1F, but a clear-cut state-dependency is absent. Secondly, the relationship between the incidences of breathing during states 1F and 2F depends on the 'drive' or motivation (presumably the blood glucose content) to breathe.

The effect of vibro-acoustic stimulation on fetal behavioral state organization

During the third trimester of pregnancy there is a gradual development of fetal behavioral states. These states are distinct and discontinuous modes of neural activity; they reflect a certain degree of maturity and/or integrity of the fetal brain and are homologous with those seen in newborn infants. Abnormal state development has been found in growth retarded fetuses and in fetuses of women with type-1 diabetes. Behavioral state organization is not easily influenced by external factors and most stimuli fail to induce a state change when the fetus is in quiet sleep (state 1F). However, fetuses do react to vibro-acoustic stimulation (VAS) with an electronic artificial larynx. This stimulus induces excessive fetal movements, prolonged tachycardia, disorganization of behavioral states, and state transitions normally not seen in healthy fetuses. The backgrounds for these excessive and unusual reactions are largely unknown. For the time being, it seems better not to use this device in clinical practice. In this review paper, data on the development of behavioral states and on fetal reactions to VAS are discussed.

Fetal Doppler velocimetry in the internal carotid and umbilical artery during Braxton Hicks' contractions

Using Doppler ultrasound, previous studies revealed a considerable increase in vascular resistance in the uteroplacental circulation during Braxton Hicks' contractions. Consequently, uteroplacental blood flow is reduced and this affects placental oxygen transfer to the fetus, causing a fall in fetal arterial PO2. In view of the important role of arterial PO2 in the regulation of cerebral blood flow in the fetus, we hypothesised that Braxton Hicks' contractions cause a decrease in cerebral vascular resistance. A study was undertaken in 16 healthy near term pregnancies, using pulsed-wave Doppler ultrasound to evaluate the influence of Braxton Hicks' contractions on cerebral vascular resistance of the fetus. Flow velocity waveforms (FVWs) were recorded of the fetal internal carotid and umbilical artery and the Pulsatility Index (PI) was calculated. During Braxton Hicks' contractions the PI in the recorded vessels did not change. Fetal heart rate showed also no changes during Braxton Hicks' contractions. These findings indicate that resistance to blood flow downstream of these arteries, is not significantly altered, suggesting that Braxton Hicks' contractions have little or no effect on fetal haemodynamics and on fetal oxygenation in the healthy near term fetus.

A mechanism leading to reduced lung expansion and lung hypoplasia in fetal sheep during oligohydramnios

Our aim was to determine the mechanism whereby oligohydroamnios causes reduced fetal lung expansion and eventual lung hypoplasia. We studied 20 fetal sheep during 2 to 9 days of oligohydramnios produced by drainage of amniotic and allantoic fluids during the last third of gestation. Oligohydramnios led to a reversible reduction in lung liquid volume of 19.5% within 48 hours. During oligohydramnios tracheal pressure, relative to amniotic pressure, rose by 1.7 mm Hg (p less than 0.001); pressures also tended to rise in the fetal pleural space and abdomen, relative to amniotic pressure, and to fall in the amniotic sac. Pressure increments, relative to amniotic pressure, which normally occur in the fetal trachea, pleural cavity, and abdomen during nonlabor uterine contractions, were significantly increased by 1.9 to 2.5 mm Hg during oligohydramnios. Oligohydramnios increased flexion of the fetal thoracolumbar spine, quantified as a reduction in the ratio of spinal radius of curvature to spine length (0.76 in controls vs 0.40 after oligohydramnios, p less than 0.001). In three sets of twins, only the fetus exposed to oligohydramnios was affected. A similar degree of spinal flexion imposed on normal fetal sheep cadavers increased abdominal (1.6 mm Hg), pleural (1.5 mm Hg), and tracheal (2.0 mm Hg) pressure, and caused a significant reduction in fetal lung expansion. We conclude that oligohydramnios in fetal sheep increases spinal flexion, leading to compression of abdominal contents, upward displacement of the diaphragm, and lung compression, favoring loss of fetal lung liquid. These changes, which are accentuated during nonlabor uterine contractions and are reversible, may lead to pulmonary hypoplasia if prolonged.

Nuchal muscle activity at different levels of hypoxemia in fetal sheep

The effects of hypoxemia on nuchal muscle activity, a parameter of gross body movements, were studied during 12 experiments in five chronically instrumented fetal lambs. Hypoxemia was accomplished by tracheal infusion of nitrogen and did not result in significant changes in fetal arterial pH and PCO2. Fetal arterial blood gases and pH were continuously measured with an extracorporeal flow-through cuvette. Nuchal muscle activity was measured by electromyography and was expressed as the percentage of time spent moving. A decrease in fetal arterial oxygen saturation to three fourths of the initial value for 2 hours was not associated with significant changes in nuchal muscle activity. When fetal arterial oxygen saturation was further reduced for 2 hours to one half, fetal nuchal muscle activity fell significantly from 34.6% +/- 10.5% during normoxemia to 20.9% +/- 13.9% during hypoxemia. However, the most pronounced changes in fetal nuchal muscle activity occurred in the first 15 minutes after the changes in arterial oxygen saturation. A considerable transient increase in nuchal muscle activity was observed during the first 15 minutes after recovery from hypoxemia. During hypoxemia there was a relative predominance of short-lasting (less than 3 minute) movements.

Heart rate variation and movement incidence in growth-retarded fetuses: the significance of antenatal late heart rate decelerations

In 37 intrauterine growth-retarded fetuses, combined 1-hour recordings of fetal heart rate and body movements were made within 24 hours of elective cesarean section. Fetal body movements were recorded simultaneously by use of real-time ultrasound. The study group was divided into two subgroups, according to the presence (n = 29) or absence (n = 8) of antepartum late heart rate decelerations. Correlations were made with umbilical blood gas values obtained immediately after cesarean section. Baseline heart rate variation was reduced below the normal range in 88% of the intrauterine growth-retarded fetuses with decelerations but in only 37% of the group without decelerations. A reduction in fetal heart rate accelerations and body movements and an increase in mean heart rate also were observed only in the group with decelerations. Late heart rate decelerations were associated with low PO2 values in both umbilical artery and vein. It is concluded that in intrauterine growth-retarded fetuses reduced heart rate variation and movement incidence correlate with the presence of late heart rate decelerations before birth and with hypoxemia at birth.