Fetal Development: Voice Processing in Normotensive and Hypertensive Pregnancies

Ideal Mode of Auditory Stimulation in Preterm Neonates in Neonatal Intensive Care Unit: A Systematic Review

The objective of this review was to find out the best mode of auditory stimulation for preterm neonates admitted to the neonatal intensive care unit. We also aimed to find out the different effects of different types of auditory stimulation in these neonates. Advanced neonatal care and technological advances in neonatal intensive care units have led to increased survival of preterm-born neonates, but this in turn leads to increased incidences of disabilities like cerebral palsy, visual impairment, delayed social development, etc. Early intervention is provided to facilitate further development and prevent delays in all domains. Auditory stimulation is proven to benefit these neonates to stabilize their vitals and improve their auditory performance in later life. Different modes of auditory stimulation have been studied worldwide, but none of the studies has presented the ideal mode of auditory stimulation for these preterm neonates. In this review, we have discussed the effects produced by different types of auditory stimulation and compared their pros and cons. For conducting a systematic review, a search strategy adopted by MEDLINE is used. A total of 78 articles published between 2012 and 2017, on the effects of auditory stimulation on preterm infants' performance were reviewed. Out of that, eight studies that met the inclusion criteria and focused on short-term and long-term effects were included in this systematic review. Search terms included preterm neonates, auditory stimulation, and early intervention. Randomized controlled trials and cohort studies were included. Auditory stimulation by maternal sound provides physiological and autonomic stability, but the behavioral states of preterm neonates improved with auditory stimulation by music therapy with lullabies. Maternal singing during kangaroo care may be recommended for providing physiological stability.

Associations between Maternal Risk Factors and Intrinsic Placental and Fetal Brain Functional Properties in Congenital Heart Disease

The relationship between maternal risk factors (MRFs) (particularly pre-gravid obesity, diabetes, and hypertension) and congenital heart disease (CHD) to placental and fetal brain outcomes is poorly understood. Here, we tested the hypothesis that MRF and CHD would be associated with reduced intrinsic placental and fetal brain function using a novel non-invasive technique. Pregnant participants with and without MRF and fetal CHD were prospectively recruited and underwent feto-placental MRI. Using intrinsic properties of blood oxygen level dependent imaging (BOLD) we quantified spatiotemporal variance of placenta and fetal brain. MRFs and CHD were correlated with functional characteristics of the placenta and fetal brain. Co-morbid MRF (hypertension, diabetes, and obesity) reduced spatiotemporal functional variance of placenta and fetal brain (p < 0.05). CHD predicted reduced fetal brain temporal variance compared to non-CHD (p < 0.05). The presence of both MRF and CHD was associated with reduced intrinsic pBOLD temporal variance (p = 0.047). There were no significant interactions of MRFs and CHD status on either temporal or spatial variance of intrinsic brain BOLD. MRF and CHD reduced functional characteristic of placenta and brain in fetuses. MRF modification and management during pregnancy may have the potential to not only provide additional risk stratification but may also improve neurodevelopmental outcomes.

Cardiac Orienting to Auditory Stimulation in the Fetus

The objective of this study was to longitudinally evaluate the cardiac response to auditory stimulation in fetuses born during their 28th gestational week. A longitudinal, within-subjects design allowed for interpretations of the cardiac response tracked from 28 to 38 weeks gestational age (GA). All mothers recited a short passage from 28 to 34 weeks GA, and their fetuses were tested at 28, 32, 33, and 34 weeks GA. Following discontinuation of maternal recitation at 34 weeks GA, testing continued at 36 and 38 weeks GA. Experimental subjects were tested with a recording of a female stranger speaking the assigned passage and control subjects tested with a novel passage. The cardiac response was evaluated visually and statistically based on the magnitude and duration of the changes in heart rate. Visually, the cardiac response transitioned from a minimal magnitude (<5 beats per minute) with short duration (<5 seconds) cardiac deceleration in both experimental and control subjects during testing from 28 to 38 weeks GA and was confirmed statistically. For all experimental subjects, however, a long duration or sustained (>5 seconds) cardiac deceleration of greater magnitude (>5 beats per minute) was detected during 34-, 36-, or 38-week test session and was confirmed using a computational algorithm in SAS. Further investigation into additional forms of auditory stimulation at different developmental time periods is needed.

Exposure to human voices has beneficial effects on preterm infants in the neonatal intensive care unit

We reviewed the literature up to March 2016 on the effects of nonmaternal voices on preterm infants' clinical outcomes. Of the 11 studies that met the inclusion criteria, 10 focused on short-term outcomes and one looked at long-term effects. The studies mainly showed that vocal stimuli increased preterm infants' stability in terms of heart rate, respiratory rate, oxygen saturation and behavioural measures. Improvements in feeding skills were also reported. The methods and the measures used in the studies were heterogeneous, making it difficult to draw reliable conclusions.

CONCLUSION

Vocal stimuli increased preterm infants' stability, but further studies are needed.

Correlation between maternal anxiety, reactivity of fetal cerebral circulation to auditory stimulation, and birth outcome in normotensive and gestational hypertensive women

This study investigated the correlation between maternal anxiety and blood flow changes through the fetal middle cerebral artery (MCA) after defined acoustic stimulation in 43 normotensive (C) and 40 gestational hypertensive (GH) subjects. Neonatal outcomes (gestational age at birth, Apgar score, birth weight) in the C and GH groups were analyzed. State (STAI-S) and trait (STAI-T) anxiety was assessed using Spielberger's questionnaire. The MCA blood flow was assessed once between 28 and 41 weeks of gestation using color Doppler ultrasound before and after application of defined acoustic stimulus. Relative size of the Pulsatility index (Pi) change (RePi) was calculated. The general hypotheses were: (1) women in GH group would have higher anxiety; (2) higher anxiety correlates with higher RePi change and poorer neonatal outcome; (3) fetuses from the GH group would have poorer neonatal outcome. Subjects from the GH group had higher STAI-T and RePi compared to the C group. A positive correlation between RePi and STAI-S, STAI-T, and systolic/diastolic blood pressure was found in both groups. There were more preterm deliveries in the GH group compared to the C group. A significant effect of STAI-T on body weight was observed in the C and GH group. There was a predictive effect of STAI-T and RePi on the C group, and STAI-S, STAI-T, diastolic blood pressure, and RePi on the GH group in terms of neonatal body weight. This study demonstrates an association between antenatal anxiety in GH women and increased fetal cerebral circulation in response to defined auditory stimulation.

Auditory object perception: A neurobiological model and prospective review

Interaction with the world is a multisensory experience, but most of what is known about the neural correlates of perception comes from studying vision. Auditory inputs enter cortex with its own set of unique qualities, and leads to use in oral communication, speech, music, and the understanding of emotional and intentional states of others, all of which are central to the human experience. To better understand how the auditory system develops, recovers after injury, and how it may have transitioned in its functions over the course of hominin evolution, advances are needed in models of how the human brain is organized to process real-world natural sounds and "auditory objects". This review presents a simple fundamental neurobiological model of hearing perception at a category level that incorporates principles of bottom-up signal processing together with top-down constraints of grounded cognition theories of knowledge representation. Though mostly derived from human neuroimaging literature, this theoretical framework highlights rudimentary principles of real-world sound processing that may apply to most if not all mammalian species with hearing and acoustic communication abilities. The model encompasses three basic categories of sound-source: (1) action sounds (non-vocalizations) produced by 'living things', with human (conspecific) and non-human animal sources representing two subcategories; (2) action sounds produced by 'non-living things', including environmental sources and human-made machinery; and (3) vocalizations ('living things'), with human versus non-human animals as two subcategories therein. The model is presented in the context of cognitive architectures relating to multisensory, sensory-motor, and spoken language organizations. The models' predictive values are further discussed in the context of anthropological theories of oral communication evolution and the neurodevelopment of spoken language proto-networks in infants/toddlers. These phylogenetic and ontogenetic frameworks both entail cortical network maturations that are proposed to at least in part be organized around a number of universal acoustic-semantic signal attributes of natural sounds, which are addressed herein.

Systematic review of maternal voice interventions demonstrates increased stability in preterm infants

We systematically reviewed how effectively maternal voice interventions supported the clinical outcomes and development of preterm infants. A total of 512 preterm infants were included in 15 studies with different designs, from January 2000 to July 2015. Live and recorded maternal voice interventions were associated with the physiologic and behavioural stabilisation of preterm infants, with fewer cardiorespiratory events, but the evidence was insufficient to evaluate the long-term effects. Well-defined determinants and clear setting conditions are needed for such interventions.

CONCLUSION

Further research that investigates the long-term efficacy and effects of live maternal voices on preterm infant development is needed.

Inner ear ossification and mineralization kinetics in human embryonic development - microtomographic and histomorphological study

Little is known about middle and inner ear development during the second and third parts of human fetal life. Using ultra-high resolution Microcomputed Tomography coupled with bone histology, we performed the first quantitative middle and inner ear ossification/mineralization evaluation of fetuses between 17 and 39 weeks of gestational age. We show distinct ossification paces between ossicles, with a belated development of the stapes. A complete cochlear bony covering is observed within the time-frame of the onset of hearing, whereas distinct time courses of ossification for semicircular canal envelopes are observed in relation to the start of vestibular functions. The study evidences a spatio-temporal relationship between middle and inner ear structure development and the onset of hearing and balance, critical senses for the fetal adaptation to birth.

Prenatal learning in an Australian songbird: habituation and individual discrimination in superb fairy-wren embryos

Embryos were traditionally considered to possess limited learning abilities because of the immaturity of their developing brains. By contrast, neonates from diverse species show behaviours dependent on prior embryonic experience. Stimulus discrimination is a key component of learning and has been shown by a handful of studies in non-human embryos. Superb fairy-wren embryos (Malurus cyaneus) learn a vocal password that has been taught to them by the attending female during incubation. The fairy-wren embryos use the learned element as their begging call after hatching to solicit more parental feeding. In this study, we test whether superb fairy-wren embryos have the capacity to discriminate between acoustical stimuli and whether they show non-associative learning. We measured embryonic heart rate response using a habituation/dishabituation paradigm with eggs sourced from nests in the wild. Fairy-wren embryos lowered their heart rate in response to the broadcasts of conspecific versus heterospecific calls, and in response to the calls of novel conspecific individuals. Thus, fairy-wrens join humans as vocal-learning species with known prenatal learning and individual discrimination.

Emergence and retention of learning in early fetal development

Prior research has demonstrated that the late-term fetus is capable of learning and then remembering a passage of speech for several days, but there are no data to describe the earliest emergence of learning a passage of speech, and thus, how long that learning could be remembered before birth. This study investigated these questions. Pregnant women began reciting or speaking a passage out loud (either Rhyme A or Rhyme B) when their fetuses were 28 weeks gestational age (GA) and continued to do so until their fetuses reached 34 weeks of age, at which time the recitations stopped. Fetuses' learning and memory of their rhyme were assessed at 28, 32, 33, 34, 36 and 38 weeks. The criterion for learning and memory was the occurrence of a stimulus-elicited heart rate deceleration following onset of a recording of the passage spoken by a female stranger. Detection of a sustained heart rate deceleration began to emerge by 34 weeks GA and was statistically evident at 38 weeks GA. Thus, fetuses begin to show evidence of learning by 34 weeks GA and, without any further exposure to it, are capable of remembering until just prior to birth. Further study using dose-response curves is needed in order to more fully understand how ongoing experience, in the context of ongoing development in the last trimester of pregnancy, affects learning and memory.

Fetal habituation in assisted conception

BACKGROUND

Neurodevelopment outcomes of children conceived by Assisted Reproductive Technology (ART)have been the subject of much recent attention. To date there are no reports of neurodevelopmental performance before birth in this group.

AIMS

To compare habituation (a measure of brain function) in fetuses conceived by assisted reproduction techniques (ART) with naturally conceived (NC) fetuses.

STUDY DESIGN

Case control study.

SUBJECTS

Women with singleton pregnancies matched for maternal age, parity and smoking were recruited in 2 groups: ART (n=20) and NC (n=20).

OUTCOME MEASURES

Sound stimuli (250 Hz, 110 dB) at 10 second intervals lasting 2 s were administered to the fetus. The end point was habituation (cessation of movement for five consecutive stimuli) or a maximum of 30 stimuli. Responses of the fetus were observed with ultrasound at 28, 32 and 36 weeks' gestation, video-recorded and anonymised for analysis.

RESULTS

At 28 weeks' gestation significantly more ART fetuses responded to sound of 250 Hz, 110 dB (p=0.02) but this difference did not persist at 32 and 36 weeks'. There was a significant increase in nonresponders as gestation advanced in the ART group. There was no difference in habituation or mean number of trials to habituate at all three gestations.

CONCLUSIONS

ART fetuses demonstrated no differences in habituation suggesting that there is no neurodevelopment delay. However, a decrease in response to sound as gestation advances might be a harbinger for poor perinatal outcomes and needs exploration.

Atypical fetal response to the mother's voice in diabetic compared with overweight pregnancies

OBJECTIVE

To characterize fetal spontaneous heart rate changes and movements and auditory-elicited heart rate changes in fetuses in diabetic pregnancies compared with those in uneventful, overweight pregnancies.

METHODS

Spontaneous heart rate and movements and maternal voice-elicited heart rate changes were observed in 46 mother-fetal pairs (n = 14 gestational diabetic and n = 32 overweight prepregnancy) at 36 (±1) weeks gestational age. Fetal heart rate changes, body movements, and breathing movements were observed for 20 minutes while the mother was at rest. Subsequently, each fetus was presented with a 2-minute audio recording of the mother's voice using the following 6-minute procedure: 2 minutes no-voice baseline, 2 minutes voice presentation, and 2 minutes no-voice postvoice period; heart rate was recorded continuously.

RESULTS

There were no differences in spontaneous heart rate changes, body movements, or breathing movements between the 2 groups. Fetuses in the overweight group showed an increase in the heart rate during the playing of their mother's voice, whereas fetuses in the diabetic group showed no response.

CONCLUSIONS

Fetuses in overweight pregnancies responded to the mother's voice with an increase in the heart rate as has been reported previously in uneventful pregnancies. The lack of response to the mother's voice in fetuses in diabetic pregnancies may represent immature neural or auditory system development, an increased sensorineural threshold, and thyroid or iron deficiency.

Atypical fetal voice processing in preeclamptic pregnancy

OBJECTIVE

To compare fetal heart rate (HR) response to the mother's voice in pregnancies complicated by preeclampsia with those of fetuses in uneventful, normotensive pregnancies.

METHOD

Fifty fetuses (n = 22, preeclampsia; n = 28, uneventful, normotensive pregnancies) between 32 and 40 weeks gestational age were recruited. Each fetus was presented with a 2-min no-sound baseline period followed by a 2-min voice period during which an audio recording of his/her mother reading a story was played through a loud speaker over the maternal abdomen at an average of 95 dBA followed by a 2-min no-voice offset period. HR was recorded continuously.

RESULTS

Fetuses in the preeclamptic group showed no response to the mother's voice when it was played. In comparison, fetuses in the uneventful, normotensive group responded to the mother's voice with a HR increase.

CONCLUSION

Fetuses in pregnancies complicated by preeclampsia show atypical auditory processing of the mother's voice. Such atypical responding may reflect a delay in auditory system maturation, functional elevation of sensorineural threshold, or decreased thyroid hormone.

[Fetal audition. Myth or reality]

Fetal sensory abilities have been considered for a long time as a philosophical question. The aim of this review is to investigate the scientifically proven knowledge about fetal audition. Fetal audition seems to depend on gestational age and sound characteristics. The onset of human fetal hearing is observed at about 26-28 weeks gestational age. Noises from the placenta, the maternal organs and the maternal voice play a major role as current in utero auditory stimuli. Many studies demonstrate that the fetus forms memories of his hearing experiences allowing some authors to use the term "fetal learning". The fetus can memorize not only his mother's voice but also more complex acoustic external sounds with a big ability of discrimination. Moreover, most studies strengthen the hypothesis of an implicit musical ability of the human brain.

Auditory processing deficits in growth restricted fetuses affect later language development

An increased risk for language deficits in infants born growth restricted has been reported in follow-up studies for more than 20 years, suggesting a relation between fetal auditory system development and later language learning. Work with animal models indicate that there are at least two ways in which growth restriction could affect the development of auditory perception in human fetuses: a delay in myelination or conduction and an increase in sensorineural threshold. Systematic study of auditory function in growth restricted human fetuses has not been reported. However, results of studies employing low-risk fetuses delivering as healthy full-term infants demonstrate that, by late gestation, the fetus can hear, sound properties modulate behavior, and sensory information is available from both inside (e.g., maternal vascular) and outside (e.g., noise, voices, music) of the maternal body. These data provide substantive evidence that the auditory system is functioning and that environmental sounds are available for shaping neural networks and laying the foundation for language acquisition before birth. We hypothesize that fetal growth restriction affects auditory system development, resulting in atypical auditory information processing in growth restricted fetuses compared to healthy, appropriately-grown-for-gestational-age fetuses. Speech perception that lays the foundation for later language competence will differ in growth restricted compared to normally grown fetuses and be associated with later language abilities.