Feasibility of Spectral Analysis as a Tool in Nursing Research to Quantify Patterns of Respiration in Premature Infants.

Background: Respiratory difficulties are a common concern in preterm infants, and they can lead to long-term health problems. Few studies have investigated the use of spectral analysis as a biomarker to quantify respiration patterns in preterm infants. Objective: To evaluate the feasibility of using spectral analysis of heart rate variability as a biomarker for the quantification of respiratory patterns in very-low-birth-weight preterm infants compared to direct observation. Methods: In a comparative, small-scale feasibility study, 18 preterm infants born during their 27th to 28th gestational week (weighing <1500 grams) participated by convenience. Respiratory patterns (regular or irregular; shallow or deep) were directly observed on the 28th week during playback of speech recording. Heart rate variability was simultaneously measured using spectral analysis of heart periods, from which the mean values influenced by respiratory sinus arrhythmia (frequencies of 0.30-1.0 Hz) were compared to each observed respiratory pattern. The magnitudes of respiratory sinus arrhythmia and the area under the curve were determined. Results: The magnitude of respiratory sinus arrhythmia (frequencies of 0.30-1.0 Hz) in infants observed to be displaying irregular shallow respiration was greater than that in infants with regular deep respiration. Further, there was a shift from lower frequencies (frequency peak = 0.30 Hz) to higher frequencies (peak = 0.70 Hz). Conclusion: In contrast with direct observation, spectral analysis allowed for the quantification of respiratory patterns in a vulnerable population of preterm infants of interest to the nursing scientific and practice community. Future directions include applying this biomarker to evaluate both developmental and pathological trends in the respiratory patterns of preterm infants.

Effect of Maternal Speech on Neural Development in Premature Infant.

INTRODUCTION: Maternal speech has been shown to benefit premature infants by improving feeding outcomes and potentiating the development of the auditory cortex. To our knowledge, limited studies have addressed the benefits of exposure to maternal speech on neural development in premature infants. The objective of this study was to investigate the effect of early controlled exposure to maternal recording a passage of speech on heart rate variability (obtained before, during, and after playback of a test stimulus of a female stranger speaking the same passage) in very low-birth-weight premature infants tracked weekly from 28 to 34 weeks. METHODS: Prospective, randomized controlled trial, longitudinal, and repeated-measures design were conducted on 49 subjects. Infants heard a recording of their mother's speech twice a day from either 28 to 34 weeks (group 1) or from 32 to 34 weeks (group 2). Spectral analysis was measured weekly for 45 seconds before, during, and after playback of maternal speech. A generalized linear mixed model was conducted to examine the 2-way interaction in the log high-frequency power between groups, genders, sessions, and conditions. RESULTS: It was found that there were no significant differences between groups before, during, and after playback of the stimulus. A significant difference, however, was noted between conditions (before vs during period). CONCLUSION: It can be concluded cautiously that playing back of maternal speech recordings to the premature infant has a beneficial impact on neural development after 32 weeks gestational age.

Maternal Voice Exposure and Its Effect on Premature Infants' Feeding Milestones: A Systematic Review.

BACKGROUND: Premature infants experience alterations in maternal stimulation (including auditory sensory alteration such as talking or singing to the infant in the neonatal intensive care unit) due to admission to the neonatal intensive care unit. Because of their physiological and neurobehavioral immaturity, infants are at an increased risk of delays in reaching feeding milestones (a key developmental milestone), which often need to be achieved before discharge. PURPOSE: This systematic review evaluated the literature regarding the effect of maternal speech on achievement of feeding milestones in premature infants. DATA SOURCES: A systematic search of CINAHL, PubMed, Web of Science, and Google Scholar from 2010 to 2021. STUDY SELECTION: Studies were selected if they examined the effect of maternal voice interventions on premature infants' feeding milestones. DATA EXTRACTION: Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used. RESULTS: Six studies were identified. This systematic review of the literature on the effects of maternal voice on feeding milestones in premature infants found equivocal results. IMPLICATIONS FOR PRACTICE: Given the inconsistent results, this systematic review does not support a change in clinical practice. However, encouragement of maternal visits is highly recommended as the additional benefits of the mother's presence may extend beyond exposure to maternal voice. IMPLICATIONS FOR RESEARCH: More research is needed including use of more homogenous samples, application of recommended decibel levels, and utilization of an adequately powered randomized controlled trial to further examine the effects of maternal voice on feeding milestones.

Measures of Lactation Outcomes in Women Delivering Preterm Infants.

BACKGROUND: Mother's own milk (MOM) is well known to decrease prematurity-related morbidities, yet mothers delivering preterm infants often produce insufficient quantities of milk to provide these benefits. Although a critical need exists for research to support lactation success in this vulnerable population, development and investigation of interventions to increase available MOM for infant consumption requires consistent, valid, and reliable measures of lactation outcomes. OBJECTIVES: The aim of this study was to compare and contrast methods of measuring lactation outcomes in mothers of preterm infants and evaluate their advantages and disadvantages. METHODS: Measures of lactation outcomes were reviewed and synthesized. Insights on best practices and future research directions are provided. RESULTS: Volume of MOM produced, lactation duration, and time to onset of secretory activation are important measures of lactation success. The most valid and reliable measure of milk production is likely weighing each vial of expressed milk combined with test weighing when infants breastfeed. Measures of lactation duration should include actual days mothers lactated rather than limiting to infant consumption of MOM as a proxy for duration and include not only whether mothers are lactating at infant discharge but whether they are also lactating at other health-relevant time points during hospitalization. Although time to onset of secretory activation is an important lactation outcome, information regarding valid and reliable indicators of onset in women delivering preterm infants is limited, and investigation of such indicators is a research priority. Variables that may affect lactation outcomes, including time to initiation of expression following delivery, duration of expression sessions, expression method, time spent in skin-to-skin care, maternal demographics and comorbidities, as well as maternal intent to lactate, must be considered when researchers investigate lactation outcomes in mothers of very low birth weight infants. DISCUSSION: Consistent and valid measures of lactation outcomes are required to produce reliable results from which evidence-based practice recommendations can be developed in order to improve lactation success in this vulnerable population.

Effect of Postpartum Depo Medroxyprogesterone Acetate on Lactation in Mothers of Very Low-Birth-Weight Infants.

Objective: This study examined the effect of postpartum administration of depo medroxyprogesterone acetate (DMPA) on milk production, time to onset of secretory activation, lactation duration, and infant consumption of mother's own milk (MOM) in mothers of preterm very low-birth-weight (VLBW) infants. Materials and Methods: We conducted a secondary analysis of data from mothers who delivered infants weighing ≤1,500 g and at ≤32 weeks' gestation. The volume of milk produced was measured on days 1-7, 14, and 21 by weighing all expressed milk on an electronic scale. Time to secretory activation was determined through self-report of a feeling of breast fullness. Information on lactation duration and the percent of feeds consisting of MOM consumed by infants was obtained from the medical records. Results: Mothers who received postpartum DMPA were more likely to be African American (72.4% versus 31.4%; p = 0.0006), unemployed (65.5% versus 44.5%; p = 0.027), and Medicaid eligible (89.7% versus 67.2%; p = 0.019). There were no differences in daily milk production between mothers who received DMPA before hospital discharge (n = 29) compared with those who did not (n = 141). When mothers who reached secretory activation before receiving DMPA were removed from analysis, receiving DMPA was associated with a later onset of secretory activation (103.7 versus 88.6 hours; p = 0.028). There were no statistically significant differences between the study groups in lactation duration or infant MOM consumption. Conclusions: DMPA, when administered postpartum to mothers of preterm VLBW infants, delayed secretory activation, but had no detrimental effect on milk production or lactation duration. Clinical Trial Registration: ClinicalTrials.gov Identifier: NCT01892085.

Indicators of Secretory Activation in Mothers of Preterm Very Low Birth Weight Infants.

BACKGROUND: Inconsistent information exists regarding indicators of secretory activation in mothers delivering very low birth weight infants. RESEARCH AIMS: To compare time to the onset of secretory activation using three separate indicators. A secondary aim examined the association between indicators of secretory activation and milk production. METHODS: Indicators of secretory activation included maternal perception, volume attainment (production of ≥ 20 mL in two consecutive expression sessions) and biomarkers (sodium and lactose) obtained at volume attainment. Milk production was measured on Days 1-7 and then weekly for 6 weeks. RESULTS: In 69 mothers of infants born ≤ 32 weeks' gestation and < 1500 g, we found no correlation in time to secretory activation between indicators. Earlier volume attainment was associated with increased milk production on Days 1-7, 14, 21, and 28 (all p < .007). Participants who exhibited both normal lactose and sodium levels produced more milk on Days 28 and 42 (p = .028 and .011), those with only normal lactose levels produced more on Day 42 (p = .026) and those with only normal sodium levels on Day 28 (p = .036). Earlier secretory activation by volume attainment was associated with increased expression frequency during Days 2-5 (all p < .014) and participants with normal biomarkers expressed more frequently during Days 2-5 (all p < .020). CONCLUSION: Mothers of very low birth weight infants are at risk for delayed secretory activation, which may decrease their milk production. Frequent expression during the first 5 days postpartum may promote earlier secretory activation. Valid methods of determining secretory activation are necessary to develop interventions promoting earlier secretory activation.

Demographic, Social, and Personal Factors Associated With Lactation Cessation by 6 Weeks in Mothers of Very Low Birth Weight Infants.

BACKGROUND: Although mother's own milk decreases prematurity-associated morbidities, mothers of infants born preterm and very low birth weight experience a significantly shorter lactation duration. Little is known regarding factors associated with lactation cessation during the hospitalization of a very low birth weight infant. RESEARCH AIM: To determine demographic, social, and personal factors associated with lactation cessation by 6-weeks postpartum in mothers delivering very low birth weight infants. METHODS: We used a retrospective, longitudinal, two-group comparison design using data from a randomized control study. Mothers of very low birth weight infants (N = 142) were enrolled from a labor and delivery unit associated with a Level 4 neonatal intensive care unit. Demographic, social, and health information was obtained from the medical records. Participants were surveyed regarding lactation goals, experience, and reason(s) for cessation. RESULTS: Participants who did not continue lactating for more than 6 weeks were more likely to be unemployed (p = .019), Medicaid eligible (p = .009), less educated (p < .031), smoke (p = .002), provide less skin-to-skin care (p = .007), and to delay the decision to provide their milk to their infant (p = .007). After Bonferroni adjustment, only minutes of skin-to-skin care remained statistically significant. Insufficient maternal milk production was the most common reason for lactation cessation. CONCLUSION: While the etiology of lactation cessation is often non-modifiable, strategies aimed at maintaining mother's own milk production, smoking cessation, increasing skin-to-skin care, and promoting an earlier decision to lactate, may prolong lactation duration in this vulnerable population.This RCT was registered (2012-00071) with ClinicalTrials.com on 6/28/2013.

Effect of Aspiration and Evaluation of Gastric Residuals on Intestinal Inflammation, Bleeding, and Gastrointestinal Peptide Level.

OBJECTIVE: To determine the effect of gastric residual aspiration and evaluation on preterm very low birth weight infants' gastrointestinal function, intestinal inflammation, and gastrointestinal mucosal bleeding. STUDY DESIGN: This single-center, randomized trial compared omission of gastric residuals vs prefeed gastric residuals in 143 infants ≤32 weeks of gestation with a birthweight of ≤1250 g for 6 weeks after birth. Serum levels of gastrin and motilin were collected between 14 and 21 days of life. Stools were collected at 3 and 6 weeks of age and analyzed for calprotectin and S100A12 levels. All stools were tested for occult blood for 6 weeks. RESULTS: Means for gastrin (P = .999) and motilin (P = .694) were similar between groups and there were no statistically significant differences in adjusted means for transformed calprotectin (P = .580), and S100A12 (P = .212). Both calprotectin (P = .003) and S100A12 (P = .002) increased from week 3 to week 6. The mean percentage of stools positive for occult blood (P = .888) were similar between the groups. CONCLUSIONS: Gastrointestinal function, intestinal inflammation, and gastrointestinal mucosal bleeding were similar whether aspiration and evaluation of gastric residuals were eliminated or not, suggesting routinely evaluating gastric residuals before every feeding may be unnecessary. TRIAL REGISTRATION CLINICALTRIALS.GOV:: NCT01863043.

Heart rate variability and inflammatory markers in neonates with hypoxic-ischemic encephalopathy.

To examine heart rate variability (HRV) and inflammatory markers as predictors for neurological injury in neonates undergoing therapeutic hypothermia for hypoxic-ischemic encephalopathy (HIE). We hypothesized that HRV would differentiate between infants with no/mild injury and infants with moderate/severe injury observed on MRI. Because HRV can be associated with the inflammatory cascade, cytokine concentrations were compared with the severity of brain injury indicated by MRI. Further, we studied the effect of temperature, sex, and mechanical ventilation on HRV. HRV was prospectively collected on neonates with HIE using spectral analysis for low and high frequency components (n = 16). A subset (n = 10) of neonates had serum available for inflammatory cytokine analysis obtained during cooling. Neonates were stratified into no/mild or moderate/severe injury based on MRI obtained after rewarming. Differences in HRV were identified; lower low frequency power predicted more injury on MRI. Additionally, in neonates with HIE after cooling procedure, HRV differed by gender. Elevated RANTES (CCL5) and decreased GM-CSF (Granulocyte-macrophage colony-stimulating factor) at 96 hours predicted less severe injury. In this small study, HRV differs between no/mild and moderate/severe injury in neonates with HIE. With further study, this may aid the clinician in real-time decision making. HRV differs by gender. Finally, inflammatory biomarkers may help elucidate the pathophysiology of HIE.

Effect of Gastric Residual Evaluation on Enteral Intake in Extremely Preterm Infants: A Randomized Clinical Trial.

Importance: Evaluating prefeed gastric residuals is considered routine care but has little supporting evidence. Objective: To determine the effect of omitting prefeed gastric residual evaluation on nutritional outcomes in extremely preterm infants. Design, Setting, and Participants: This single-center randomized clinical trial compared the omission of gastric residual evaluation with prefeed gastric residual evaluation. Infants were recruited from a level 4 neonatal intensive care unit and were enrolled from October 17, 2013, to October 8, 2016, and then followed up for 6 weeks after birth. Eligible participants were infants born at 32 or fewer weeks' gestation with a birth weight of 1250 g or less; they were enrolled within 72 hours after birth and within 24 hours after feeding initiation. All participants (N = 143) were included in the modified intent-to-treat analysis, which was conducted from March to July 2018. Interventions: The residual group underwent prefeed gastric residual evaluation; the no residual group did not. Feeding decisions were made according to nutritional guidelines, and infants received only human milk. Main Outcomes and Measures: The primary outcome was weekly enteral nutrition intake in mL/kg for 6 weeks after birth. Results: Of 143 infants, 74 (51.7%) were randomized to undergo gastric residual evaluation (residual group) and 69 (48.3%) to omitted gastric residual evaluation (no residual group). The residual group comprised an even number of male and female infants (37 [50.0%]) with a mean (SD) gestational age of 27.1 (2.4) weeks and a mean (SD) birth weight of 888.8 (206.6) grams, whereas the no residual group had more male infants (36 [52.17%]), a mean (SD) gestational age of 27 (1.2) weeks, and a mean (SD) birth weight of 915.2 (180) grams. The no residual group had feedings that advanced more quickly compared with the residual group (mean weekly increase, 20.7 mL/kg/d vs 17.9 mL/kg/d; P = .02) and consumed more feedings at weeks 5 (137.2 [95% CI, 128.6-145.8]; P = .03) and 6 (141.6 [95% CI, 133.2-150.0]; P = .03). Among the secondary outcomes, the no residual group had higher mean estimated log weights (7.01 [95% CI, 6.99-7.02] vs 6.98 [95% CI, 6.97-7.00]; P = .03), had fewer episodes of abdominal distention (0.59 [95% CI, 0.34-1.01] vs 1.79 [95% CI, 1.27-2.53]; P = .001), and were discharged 8 days earlier (4.21 [95% CI, 4.14-4.28] vs 4.28 [95% CI, 4.19-4.36]; P = .01). Odds for necrotizing enterocolitis (0.058 [95% CI, 0.018-0.190] vs 0.026 [95% CI, 0.006-0.109]), death (0.004 [95% CI, 0.0003-0.046] vs 0.012 [95% CI, 0.001-0.131]), late-onset sepsis (0.970 [95% CI, 0.67-1.40] vs 1.38 [95% CI, 0.97-1.94]), and ventilator-associated pneumonia (0.084 [95% CI, 0.033-0.214] vs 0.056 [95% CI, 0.019-0.168]) were similar between groups. Conclusions and Relevance: Among extremely preterm infants, the omission of gastric residual evaluation increased the delivery of enteral nutrition as well as improved weight gain and led to earlier hospital discharge; these results may translate into evidence-based practice. Trial Registration: ClinicalTrials.gov identifier: NCT01863043.

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.

Association of timing of initiation of breastmilk expression on milk volume and timing of lactogenesis stage II among mothers of very low-birth-weight infants.

BACKGROUND: Feeding breastmilk to premature infants decreases morbidity but is often limited owing to an insufficient milk supply and delayed attainment of lactogenesis stage II. Early initiation of milk expression following delivery has been shown to increase milk production in mothers of very low-birth-weight (VLBW) infants. Although recommendations for milk expression in this population include initiation within 6 hours following delivery, little evidence exists to support these guidelines. This study compared milk volume and timing of lactogenesis stage II in mothers of VLBW infants who initiated milk expression within 6 hours following delivery versus those who initiated expression after 6 hours. SUBJECTS AND METHODS: Forty mothers of VLBW infants were grouped according to when they initiated milk expression following delivery. Group I began milk expression within 6 hours, and Group II began expression after 6 hours. Milk volume was measured daily for the first 7 days and on Days 21 and 42. Timing of lactogenesis stage II was determined through mothers' perceptions of sudden breast fullness. RESULTS: Group I produced more breastmilk during the initial expression session and on Days 6, 7, and 42. No difference in timing of lactogenesis stage II was observed. When mothers who began milk expression prior to 1 hour following delivery were removed from analysis, benefits of milk expression within 6 hours were no longer apparent. CONCLUSIONS: Initiation of milk expression within 6 hours following delivery may not improve lactation success in mothers of VLBW infants unless initiated within the first hour.

Fetal response to live and recorded maternal speech.

The purpose of this study was to compare the fetal response to live and recorded maternal speech following a lengthy history of exposure to a passage spoken by the mother. Participants comprised a convenience sample of 21 pregnant women. The women recited an assigned passage (nursery rhyme) twice daily from 28 to 34 weeks' gestational age (GA), and their fetuses were tested at 34 weeks' GA. During testing, fetal heart rate and movement were measured in response to two different formats of the assigned passage: maternal live voicing and a recording of the mother speaking the passage. The fetal cardiac response varied depending upon the format; however, fetal movement did not. A minimal cardiac deceleration occurred in response to live voicing compared to a cardiac acceleration in response to the recorded format. This is the first study to show differences in the fetal cardiac response to a passage spoken live compared to a recording of the passage following a lengthy history of controlled fetal exposure to the multimodal characteristics of maternal speech. Given the differential response to a live voicing compared to a recorded format, future study that incorporates lengthier exposure to the multimodal characteristics of maternal speech may be warranted.

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.

Strategies to increase milk volume in mothers of VLBW infants.

The provision of breast milk to premature VLBW infants is associated with significant health benefits. Unfortunately, the delivery of breast milk to these vulnerable infants is often limited due to insufficient maternal milk supply. Several interventions have been investigated with respect to increasing milk volume in mothers of VLBW infants but confusion exists concerning the interventions' effectiveness. The purpose of this systematic review is to critique the evidence regarding specific milk expression strategies that aim to improve milk volume in mothers of VLBW infants.Published article references, electronic databases, dissertations and theses, and select conference proceedings were searched with the goal of finding studies that target VLBW infants and milk expression techniques in which breast milk volume was an outcome. Analysis of evidence revealed an association between increased milk volume and early initiation of expression, increased frequency of expression, and provision of kangaroo care. The use of simultaneous or sequential milk expression and duration of milk expression sessions were not found to significantly improve milk volume. These results may be used to formulate specific strategies designed to increase breast milk volume in this population.

Effect of breast milk on hospital costs and length of stay among very low-birth-weight infants in the NICU.

PURPOSE: Care of the very low-birth-weight (VLBW) infant is associated with prolonged hospitalization and increased hospital costs. Specific complications of prematurity, including necrotizing enterocolitis (NEC), late-onset sepsis (LOS), and feeding intolerance, contribute to increased cost and length of hospitalization in this population. The provision of breast milk to VLBW infants has been associated with decreased incidence of NEC and LOS as well as fewer days required to achieve full enteral feedings. The purpose of this study was to determine the impact of breast milk on length of hospitalization and hospital costs among VLBW infants in the neonatal intensive care unit (NICU). SUBJECTS: A total of 80 infants weighing less than 1500 g, born prior to 32 weeks' gestation and who remained in the home hospital until discharge. DESIGN: This descriptive comparative study examined cost of hospitalization and length of stay between 2 groups of VLBW premature infants fed either exclusively formula (n = 40) or at least 50% breast milk (n = 40) during their hospitalization. METHODS: A retrospective chart review was used to collect information concerning patient demographics, discharge information, and nutritional variables. Information regarding hospital costs was obtained from the hospital's patient accounting office. MAIN OUTCOME MEASURES: Independent t tests were used to compare demographic data, length of hospitalization, and cost of care between the 2 groups. PRINCIPAL RESULTS: No statistically significant differences in length of stay or cost of care were found between infants fed at least 50% breast milk and those who were exclusively formula fed. Descriptive data concerning length of stay and cost of care for VLBW infants and those infants weighing less than 1000 g are presented. CONCLUSION: This article presents a descriptive comparative study on the effect of providing at least 50% breast milk feedings compared with formula feeding on days to discharge and cost of hospitalization in VLBW infants in the NICU. It also provides information concerning cost of care and length of stay in VLBW and infants weighing less than 1000 g.

Safe sound exposure in the fetus and preterm infant.

Exposure to sound can have beneficial and harmful effects on the developing fetus and preterm infant. Although recommendations for safe exposure to sound have existed for more than three decades, reports indicate that these recommendations are not being followed. Recommendations are made to promote attention to the problem of unsafe exposure to sound in early development, and a multidisciplinary team, including representatives from disciplines beyond medicine and nursing, must redress safe exposure.

Exposure to maternal voice in preterm infants: a review.

The mother's voice, along with other developmentally appropriate sensory events (ie, touch, light, smells), stimulates maturation of the sensory systems and helps shape normal fetal development. While vast changes in the neonatal intensive care unit have occurred over the last 2 decades, little research has addressed the loss of exposure to maternal voice for the preterm infant. To address this gap, we compared studies that directly investigated effects of exposure to maternal voice on preterm infants. Studies reviewed were conducted between 1972 and 2007. All presented recordings of maternal voice at sound levels above current recommendations, and few of the findings reached statistical significance. Some potentially positive developmental effects were indicated. Future study of the effects of exposure to maternal voice on preterm infants using recommended sound levels is needed.

Maternal voice and short-term outcomes in preterm infants.

This study explored effects of exposure to maternal voice on short-term outcomes in very low birth weight preterm infants cared for within an neonatal intensive care unit (NICU) without an ongoing program of developmental care. Using a comparative design, 53 infants born during their 27th to 28th postmenstrual week were sampled by convenience. Experimental groups were exposed to maternal voice during two developmental time periods. Group 1 listened to a recording of their mothers reciting a rhyme from 28 to 34 postmenstrual weeks. Group 2 waited 4 weeks and heard the recording from 32 to 34 weeks. The control group received routine care. The primary analysis of combined experimental groups compared to the control group revealed that the experimental infants experienced significantly fewer episodes of feeding intolerance and achieved full enteral feeds quicker compared to the control group. Further, in an analysis evaluating all three groups separately, it was noted that Group 1 experienced significantly fewer episodes of feeding intolerance compared to the control group. Study findings warrant further investigation of exposure to maternal voice and the developmental timing at which exposure is begun.

A longitudinal description of heart rate variability in 28--34-week-old preterm infants.

The purpose of this study was to longitudinally describe changes in heart rate variability (HRV) from 28 to 34 weeks postmenstrual age (PMA). A convenience sample of 31 low-risk preterm infants participated. HRV was quantified using a spectral analysis of heart periods and recorded during seven weekly test sessions from an electrocardiogram (ECG) signal. The total range of frequency components (0.04-2.0 Hz), high-frequency (HF) components (0.30-1.3 Hz), and ratio of low-to-high frequency (LF/HF) components (0.04-0.20/ 0.30-1.3 Hz) were measured. A mixed general linear model analysis revealed no significant change over weekly test sessions for the total, the high, and the ratio of LF/HF components. A significant interaction effect was, however, noted in the HF components for test session x gender (df = 1; F = 4.85; p = .030). With increasing age, the HF components for females increased or displayed a pattern of HRV indicative of a more mature autonomic nervous system (ANS). Study findings warrant further investigation of the impact of gender on normative descriptions of HRV.