Infant Massage as a Stress Management Technique for Parents of Hospitalized Extremely Preterm Infants

Abstract

Mothers of infants born extremely preterm requiring prolonged medical intervention in the Neonatal Intensive Care Unit (NICU) are at high risk of developing stress. Parent-administered infant massage is a well-established, safe intervention for preterm infants with many developmental benefits, but the published literature has mostly examined its impact on infants and parents through self-reported or observational measures of stress. The aim of this study was to measure salivary cortisol, a biomarker for stress, in extremely preterm infants and their mothers immediately pre and post parent-administered infant massage in order to detect potential changes in physiologic stress. Twenty-two mother-infant dyads completed massage education with a physical or occupational therapist. All dyads provided salivary cortisol samples via buccal swab immediately pre- and post-massage at the second session. Of mothers determined to be “cortisol responders” (15/22), salivary cortisol levels were lower after massage (pre- minus post- level: −26.47 ng/dL, [CI=−4.40, −48.53], p=.016, paired t-test). Our primary findings include a clinically significant decrease (as measured by percent change) in maternal cortisol levels immediately post parent-administered massage, indicating decreased physiological stress. Integration of infant massage into NICU clinical practice may support maternal mental health, but further powered studies are necessary to confirm findings.

Introduction

Preterm birth, or birth prior to 37 weeks gestation comprises about 11.5% of all births, is the most frequent cause of infant mortality (Callaghan et al., 2006), and is one of the most frequent causes of neurodevelopmental disorders in children (Schieve et al., 2016). Infants born extremely preterm, or before 28 weeks gestation, require prolonged medical intervention in the Neonatal Intensive Care Unit (NICU). The mother’s involvement in the infant’s care may be limited due to the complex medical management and limited knowledge of how to safely interact with their fragile infant, which may increase the risk for maternal mental health concerns (Callaghan et al., 2006; Trumello et al., 2018). Maternal anxiety and depressive symptoms have been associated with altered maternal-infant interaction and worse developmental outcomes of the infant (Holditch-Davis et al., 2014, Hofheimer et al., 2020, de Cock et al., 2017).

Longitudinal studies of preterm infants have demonstrated that negative developmental outcomes associated with maternal mental health may persist from toddler age (Greene et al.; 2018, Huhtala et al. 2012) into middle childhood (Jaekel et al., 2012; Kleine et al., 2020). Other examples of these associations include the relationship between elevated maternal anxiety in the first month of life and worse fine motor scores at 20 months corrected age, as well as increased behavioral problems in early childhood (Greene et al., 2018; Huhtala et al., 2012; Kleine et al., 2020). Decreased post-partum psychological well-being in mothers, as measured by the Spielberger State-Trait Anxiety Index (Spielberger et al. 1983), has also been associated with worse mental health in the child, as measured by the Social Responsiveness Scale (Sturm et al., 2017) in preschool (Kleine et al., 2020).

Researchers propose that negative infant, toddler, and childhood outcomes might be improved by intervening early in the post-partum period to improve psychological well-being in mothers (Jaekel et al., 2012). In order to address this essential need, many hospital programs have implemented programmatic and institutional changes to incorporate the family into the infant’s care in order to improve parent mental health and, consequently, infant outcomes (Greene et al., 2018; Jaekel et al., 2012; Kleine et al., 2020; Moura et al., 2017).

Emerging evidence suggests that maternal-infant dyadic interaction may reduce salivary cortisol, a biomarker for stress, in infants (Mörelius et al., 2012; White-Traut et al., 2009). Skin-to-skin holding over a period of one hour in the NICU results in increased oxytocin levels in mothers, fathers, and infants and decreased cortisol in the infants (Vittner et al., 2018). These changing hormonal levels were also associated with improved responsiveness and synchrony in the parent-infant relationship as measured by videos of parent-infant interaction scored with the Dyadic Mutuality Code, an observational tool that measures reciprocal responsiveness in parent-infant dyads (Vittner et al., 2018).

While skin-to-skin holding remains the gold standard for providing developmentally supportive care for preterm infants and their parents in the NICU, Gonya et al. (2017) found a steep decline in frequency of skin-to-skin care provided by the parent at approximately 30 weeks postmenstrual age, despite potential for continued infant and parent benefits. While little evidence exists to support causality, a greater focus on transitioning preterm infants from gavage feeds to oral feeding around 30–32 weeks postmenstrual age based on respiratory status and developmental readiness may influence parent-infant interaction (Brun et al., 2020; Casavant et al., 2015; Fontana et al., 2018; Jackson et al., 2016; Ostadi et al., 2020). Full oral feeding is a criterion for discharge from the hospital; thus, when the transition away from gavage feedings begins, parents probably are more engaged with supporting this transition than in extended periods of skin-to-skin holding.

Another form of skin-to-skin care - parent-administered infant massage - has been associated with decreased pain response and improvements in weight gain, social engagement, overall development, responsiveness/attentiveness/alertness, mother-infant synchrony, mutual attentiveness, and improved infant temperament (Juneau et al., 2015; Kanagasabai et al., 2013; Newnham et al., 2009; Pineda et al., 2017; White-Traut et al., 2002). The Massage+ intervention (White-Traut et al., 2021) originally referred to as the Auditory-Tactile-Visual-Vestibular (ATVV) intervention (White-Traut et al., 2002), incorporates infant massage into a safe, multi-sensory protocol that is well-tolerated by preterm infants and demonstrates high acceptability among mothers (Holditch-Davis et al., 2013; White-Traut et al., 2004). Infant massage for the mother-infant dyad is an especially appropriate skin-to-skin intervention to supplement the declining frequency of skin-to-skin care during a time of increased focus on oral feeds because it can be administered by the mother in 15–20 minutes at the infant’s bedside (Juneau et al., 2015; Kanagasabai et al., 2013; Newnham et al., 2009; White-Traut et al., 2002). Furthermore, infant massage is commonly implemented in the same time frame that infant social behaviors are emerging (White-Traut et al., 2002).

Various multi-sensory interventions involving infant massage found decreased levels of anxiety, stress, and depressive symptoms in mothers upon completion as compared to mothers in control groups, both over time and in a single session (Afand et al., 2017; Feijó et al., 2006; Holditch-Davis et al., 2014; Matricardi et al., 2013; Welch et al., 2016; Xie et al., 2019). Additionally, benefits of Massage+ persisted after discharge at long-term follow up, with improved levels of maternal responsiveness during play and an improved home environment noted as compared to mother-infant dyads who did not complete this intervention (Holditch-Davis et al., 2014; White-Traut et al., 2013).

While reduced cortisol levels have been found in healthy, term infants after Massage+ implementation (White-Traut et al., 2009), these outcomes have not been measured in preterm infants or their parents. Prior studies have only examined the impact of parent-administered infant massage on preterm infants and parents through self-reported or observational measures of stress. In order to better understand the potential mechanism by which massage is effective in reducing stress, we measured salivary cortisol response, a biomarker for stress, in extremely preterm infants and their mothers immediately before and after infant massage in order to detect potential changes in stress at the biological level. We hypothesized that mothers and extremely preterm infants participating in parent-administered infant massage would demonstrate decreased levels of salivary cortisol after a single massage session.

Methods

Subjects

This data was collected as part of the TEMPO (Therapist Education and Massage for Parent-Infant Outcomes) Study (McCarty et al., 2023a; McCarty et al., 2023b). The study design was a prospective single group, non-randomized study completed in the Neonatal Critical Care Center at UNC Children’s Hospital. Inclusion criteria for the TEMPO Study were: 1) gestational age less than or equal to 28 weeks; 2) within the first 4 weeks of life; 3) biological mother or father who speaks English. Exclusion criteria were: 1) a medical condition, such as abnormal bone density or a genetic abnormality, that would limit the ability to perform massage; and 2) parents who were unwilling or unable to engage in all parts of the TEMPO study. Infants meeting the inclusion criteria were identified by the Principal Investigator when a physical therapy (PT) referral was received, and if a medical condition that precluded massage was not present, the family was approached by a member of the study team for consent. All participating parents completed informed consent for themselves and on behalf of their infant.

Of the 32 parent-infant dyads enrolled, 6 were transferred to outside hospitals, and 2 infants died prior to massage education intervention. One mother declined salivary cortisol testing, and one mother could not be present for the massage session. In total, 22 female parents and 1 male parent completed massage sessions and cortisol collection. Recognizing that cortisol levels may vary between sexes (Balodis et al., 2010; Kirschbaum et al., 1992; Liu et al., 2017; Zimmer et al., 2003) and may fluctuate in the post-partum period (Conde & Figueiredo, 2014; Duthie & Reynolds, 2013), we performed our analysis with only female parents and excluded the one male parent in this study. In this manuscript reference to “mothers” indicates that all parents in the sample were of female sex.

Procedure

This study underwent full review and was approved by the Institutional Review Board of the University of North Carolina at Chapel Hill. The TEMPO intervention was provided in addition to the unit’s therapy standard of care, which does not currently include infant massage education. Details of the TEMPO intervention using the Template for Intervention Description and Replication (TIDier) (Hoffman et al., 2014) can be found in Appendix A. Infant massage was one of the main components of the TEMPO program and is the focus of this investigation.

Massage Intervention

Infant massage was incorporated into the therapy plan of care when the infant could demonstrate physiologic stability and maintain a normal body temperature with reasonable support outside the incubator, at approximately 33–34 weeks postmenstrual age (PMA). All study therapists were trained by an experienced PT (DM) prior to study initiation using the Massage+ (White-Traut et al., 2021). This protocol is accessible to parents and therapists online at Pathways.org (Pathways, n.d.).

At 33 weeks PMA, the primary PT or occupational therapist (OT) performed infant massage to determine infant readiness for massage. Modifications to this protocol were minimal but included deferring massage to the infant’s face and chest in the setting of nasal cannula or EKG placement, partially swaddling the infant to maintain body temperature, and use of massage medium. In this unit, providers preferred that infants be massaged using Aquaphor ointment to reduce skin friction, and Aquaphor was dispensed individually to each infant through a provider pharmacy order requested by the therapist. The infant was determined to respond appropriately to massage by demonstrating the following: 1) maintained physiologic stability during massage, 2) did not demonstrate increased motor stress signs, 3) did not have skin irritation within 24 hours following application of Aquaphor. If infant demonstrated massage readiness, then the therapist scheduled a massage education session with the parent within one week. If the infant did not tolerate the massage, the therapist readministered the massage protocol one week later. No infants in this study developed skin irritation following Aquaphor administration.

For the parent massage education session, the therapist demonstrated massage on a doll using verbal cues and written instructions to guide the mother in administering massage on the infant. The parent administered massage to their infant while seated at the bedside, and the infant rested semi-swaddled in the parent’s lap. A laminated massage education handout with pictures and verbal descriptions was provided to the parent. The massage techniques consisted of moderately firm effleurage strokes to the extremities and back followed by 5 minutes of gentle rocking of the infant (White-Traut et al., 2002).

PTs or OTs leading the intervention, monitored vitals throughout in order to ensure that the infant remained physiologically stable and appropriate for massage. The infant’s bedside nurse was also available to monitor vitals and intervene if necessary. Once the therapist determined the parent’s ability to safely administer massage, usually after 2 massage education sessions, they were encouraged to practice infant massage at each NICU visit outside of TEMPO sessions. The mother’s comfort with massage and infant response to massage were discussed at subsequent weekly TEMPO visits with the therapist to ensure no development of adverse effects.

Measures

Salivary Cortisol:

Salivary cortisol is an established biomarker for both physical and psychological stress, and this measurement technique is often preferred to more invasive forms of cortisol assessment (eg., blood draw) (Kirschbaum & Hellhammer, 1989). Additionally, salivary cortisol levels are commonly used to assess stress level changes in a same day pre-post design (Alarcón-Yaquetto et al., 2021; Durán-Carabali et al., 2021; Gaab et al, 2003; Liu et al., 2017). These samples were taken utilizing collection kits and procedures outlined by Salimetrics (https://salimetrics.com/saliva-collection-methods-devices/) (Salimetrics, n.d.).

In order to optimize flexibility of education for parents, we did not strictly regulate time of day for the parent massage administration and salivary cortisol collection. For parents that were able, we requested that massage education take place between the hours of 10:30 am and 1:30 pm to reduce the span of time for collection. Fifteen of the 22 mothers were able to complete collection during these hours. The remaining mothers completed their collections earlier in the morning or later in the afternoon, but not during evening hours. Salivary cortisol levels were collected by trained research personnel via buccal swab immediately before and after the second of 2 massage education sessions. For parents of twins, the first salivary cortisol sample was collected before massage began with the first infant, and the second salivary cortisol sample was collected after massage with both infants was completed.

Saliva samples were collected using the SalivaBio Oral Swab (exclusively from Salimetrics, State College, PA), a synthetic swab specifically designed to improve volume collection and increase participant compliance and validated for use with saliva. Parents were asked to not eat or drink 15 minutes prior to saliva collection. Per collection instructions, the research assistant read all printed instructions to the parent at the time of collection. With gloved hands, the research assistant tipped the oral swab directly into the parent’s open mouth. Parents were instructed to hold a swab under their tongue as the researcher set a timer for 60 seconds. At the end of this 60 second period, the parent then spit the swab directly into the swab tube, which was capped and labeled with 2 patient identifiers prior to sending to the laboratory.

Samples were sent immediately to the hospital laboratory through the hospital tubing system where they were stored at −20 degrees Celsius and shipped to the Mayo Clinic Laboratory for processing within 1 week. Samples were processed within 5–7 days. All sample handling and processing standards were maintained according to Salimetrics collection instructions (Salimetrics, n.d.).

Data Analysis

Descriptive statistics were calculated for each time point of salivary cortisol collection. Paired t-tests were conducted to detect change between pre- and post-massage cortisol levels with a p value of <0.05 as criterion for statistical significance. Percent change was determined by dividing the difference between pre and post cortisol levels by the pre measure, and then multiplying by 100. Analyses were completed using Stata/MP 16.1.

Results

Twenty-two mothers completed the infant massage portion of this study, which included one initial massage education session followed by a second massage session when salivary cortisol was collected. The majority of participants were married, not Hispanic, white, had a college or graduate degree, and had private insurance (Table 1). Infants had an average birth gestational age of 25.93 weeks. For 31.8% of mothers, this was their first pregnancy, and for 59.1% of mothers, this was their first pregnancy resulting in live birth after 20 weeks gestation. Only one mother had twins, and she performed infant massage on both infants. Despite strict adherence to salivary cortisol collection protocol, in all infants, either one or both samples had insufficient levels of cortisol to assess pre and post changes; therefore, only results for parents are included in this study. All infants were able to tolerate infant massage and regulate body temperature outside of an incubator at approximately 33–34 weeks gestational age and 1500 grams. No massage sessions were terminated prematurely due to infant intolerance or skin irritation.

Table 1:

Maternal Characteristics

	Married	Single	Unknown
Marital Status	72.7% (16)	22.7% (5)	4.6% (1)
	High School Diploma	Partial College or Associate’s Degree	College Degree	Graduate Degree
Highest Level of Education	9.1% (2)	27.3% (6)	27.3% (6)	36.3% (8)
	Private	Public Insurance	Self-Pay/Uninsured	Other	Unknown
Medical Insurance	59.1% (13)	22.7% (5)	9.1% (2)	4.5% (1)	4.5% (1)
	Not Hispanic or Latino	Hispanic or Latino	Unknown or Prefer Not to Say
Ethnicity	86.3% (19)	9.1% (2)	4.5% (1)
	White	Black	Unknown or Prefer Not to Say	More than One Race
Race	59.1% (13)	22.7% (5)	13.6% (3)	4.5% (1)
	Mean (SD)
Number of Pregnancies (including current one)	2.76 (2.05)
	Mean (SD)
Number of Times Parent has given Birth to Baby of Gestation Age of 20 Weeks or More	1.52 (0.75)
	Mean (SD)
Gestational Age of Infant (Weeks)	25.93 (1.40)

Results of a paired t-test for all 22 mothers revealed a difference in pre- to post-infant massage cortisol levels with a p-value of 0.024 (−18.05 ng/dL, [CI=−2.58, −33.52]) (Table 2). The cortisol test does not detect values <50 ng/dL, and 7 mothers measured <50 ng/dL at both pre- and post-infant massage collection times. Therefore, the change values associated with these 7 participants when considering the full cohort of 22 parents was zero. In the remaining 15 samples with cortisol levels >50 ng/dL where a value other than zero was detected, a paired t-test revealed a larger significant reduction in cortisol levels (−26.47 ng/dL, [CI=4.40, 48.53], p=0.016). Average percent change from pre- to post-infant massage in this group of 15 mothers was 20.1%, which exceeds the recommended 15.5% threshold to identify “responders” vs. “non-responders,” indicating a true stress response (Miller et al., 2013). Only one parent demonstrated an increase in salivary cortisol from pre- to post massage administration (+55 ng/dL). See Figure 2.

Table 2:

Maternal Salivary Cortisol Levels from Pre- to Post-Infant Massage

N	Group Change (Mean, Median) ng/dL	Percent Change (Mean, Median) ng/dL	Standard Deviation	Range of Change ng/dL	Confidence Interval(95%)	p-value
22	−18.05, −11	13.7, 11	34.89	−108 to +55*	(−2.58,−33.52)	.024**
15	−26.47, −20	20.1, 20†	39.84	−108 to +55*	(−4.40, −48.53)	.016**

^†Group average exceeds recommended 15.5% threshold to indicate true stress response

^*Negative score indicates a decrease in salivary cortisol from pre- to post-massage while a positive score indicates an increase in salivary cortisol

^**p-value <.05 indicates significant difference

Figure 2: Changes in Maternal Salivary Cortisol Levels from Pre- to Post-Massage.

*Blue lines denote a change from pre to post for individuals included in the final N = 15 sample. The red line represents all participants whose pre and post levels were < 50 ng/d (N=7)

Discussion

The key finding of this study is that participating in a single 15–20 minute parent-administered massage session led to a decrease in cortisol levels for cortisol-responding mothers of extremely preterm infants, which partially supported our original hypothesis. We were unable to evaluate the impact of massage in infants due to insufficient levels of salivary cortisol collected.

Previous studies have also reported decreased stress as a result of massage interventions; however, these were more commonly assessed with self-report measures or over longer periods of time (Afand et al., 2017; Feijó et al., 2006; Holditch-Davis et al., 2014; Matricardi et al., 2013; Welch et al., 2016; Xie et al., 2019). Holditch-Davis et al. (2014) found that over a long term period (ie., 12 months), ATVV interventions led to decreased parenting stress and a faster decline in depressive symptoms after two months of intervention. In two studies of 8-minute infant massage sessions, mothers’ anxiety, as measured by the Spielberger State Anxiety Inventory, decreased immediately after the massage (Afand et al., 2017; Feijó et al., 2006). However, these studies were not performed exclusively with extremely preterm infants (mean gestational age at birth ranging from 27–31 weeks) (Afand et al., 2017; Feijó et al., 2006; Holditch-Davis et al., 2014; Matricardi et al., 2013; Welch et al., 2016; Xie et al., 2019). Together, these studies support that preterm infant massage can decrease maternal psychological stress.

In this study, one mother’s salivary cortisol levels increased post-massage; however, this female parent’s baseline cortisol levels were outliers both pre- and post-massage. For example, baseline cortisol levels for this female were 323 ng/dL, while the median baseline cortisol level for the rest of the female sample was 87 ng/dL. It is possible that this mother had a different stress response because of baseline differences, or that the conditions of research participation in saliva collection and/or administering infant massage actually increased the stress response.

Most studies investigating the impact of infant massage on infants focused on long-term developmental outcomes, such length of hospital stay, time to transition to nipple feeding, and neuromotor scores, rather than short-term changes in maternal stress (Kanagasabai et al., 2013; White-Traut et al., 2002, 2004). While we were not able to assess salivary cortisol levels in our sample of extremely preterm infants, White-Traut et al. (2009) reported that one session of ATVV intervention decreased levels of salivary cortisol in infants born at or after 36 weeks gestation, and Vittner et al. (2018) found similar decreases in infant cortisol following skin-to-skin holding.

There is no clearly defined threshold for a minimal detectable change (MDC) or minimal clinically important difference (MCID) for salivary cortisol in the literature that we could reference to determine clinical significance. Miller et al. (2013) suggested that a change of 43.28 ng/dL was the threshold for distinguishing cortisol responders from non-responders; however, there are a number of reasons why using an absolute value to measure meaningful change may not be the most appropriate method. There are noted sex differences in both basal levels of salivary cortisol and absolute change in salivary cortisol levels in response to a stressful or relaxing event (Balodis et al., 2010; Kirschbaum et al., 1992; Liu et al., 2017; Zimmer et al., 2003). Sex differences are also exacerbated in the postpartum period, as the hypothalamic-pituitary-adrenal (HPA) axis, which regulates salivary cortisol, is hyporesponsive in the immediate postpartum period for women, and men display increases in cortisol during this same timeframe (Conde & Figueiredo, 2014; Duthie & Reynolds, 2013). Furthermore, chronic stress can lead to decreased basal levels of salivary cortisol and decreased responsiveness of the HPA axis, which has been demonstrated in mothers of children with cerebral palsy and in parents the day after their child’s admission to a hospital (Angelhoff et al., 2019; Bella et al., 2011). Due to the numerous factors that can influence salivary cortisol levels, an absolute MDC/MCID may not be the most appropriate method to determine clinical significance of cortisol changes in this population.

In addition to quantifying an absolute value, Miller et al. (2013) also introduced the concept of calculating percent change as a way to identify clinically meaningful changes in salivary cortisol levels. For reasons previously discussed, a fixed threshold criteria may be a better representation of the magnitude of change than an absolute value. The average percent change in this study for cortisol responders (20.1%) exceeded Miller’s recommended percent change (15.1%) to identify cortisol responders from non-responders, indicating that the 15/22 mothers whose cortisol levels were >50 ng/dL at both pre and post time points likely experienced a clinically significant effect (Miller et al., 2013). While this technique is on the whole effective, some individuals, such as those with a history of chronic stress, may be considered “non-responders” and will not demonstrate a shift in salivary cortisol due to decreased responsivity of the HPA axis (Bella et al., 2011).

Future research should seek to determine additional ways to quantify meaningful change in biomarkers like salivary cortisol. One potential method is to examine correlations between measures of salivary cortisol and self-reported measures of stress pre- and post-massage intervention; however, it is unclear how well self-report measures correlate with changes in salivary cortisol, as one study reported no correlation (Aguilar-Raab et al., 2021) and others reported mixed (Maruyama et al., 2012; West et al., 2004) or strong correlations (Bedini et al., 2017; Harville et al., 2009). Another method to detect clinical significance is to consider how cortisol levels change in relation to other hormones. Some evidence suggests that changes in cortisol and oxytocin, a hormone linked to bonding, are moderately inversely correlated and should therefore be measured concurrently pre- and post-interventions designed to reduce stress and increase bonding (Vittner et al., 2018). Elnazer et al. (2021) have found that measures of chronic stress levels, as measured by hair cortisol, may be most appropriate for individuals considered cortisol “nonresponders” to interventions designed to reduce stress over long-term periods. Nevertheless, these areas continue to require future research to determine the best method of evaluating the relationship of salivary cortisol to clinical symptoms of stress in parents, both male and female, of extremely preterm infants.

Maternal satisfaction and improved health outcomes have been noted with massage-based interventions (Holditch-Davis et al., 2013); however, more research on ways to increase parent adherence to desired interventions is still needed (Letzkus et al., 2021). Parents report preferring multiple modes of instruction about how to interact with their infants, with direct observation of a therapist tending to be the most popular mode of instruction (Dusing et al., 2008). It is also important to consider parent education level when designing intervention instructions (Byrne et al., 2019).

Our study findings align with results from previous studies examining salivary cortisol reductions during skin-to-skin care (Vittner et al., 2018, Gonya et al., 2017)) between infant and parent – highlighting the important biological impact of touch in the newborn period. Other studies have documented altered cortisol levels in parents of children with chronic health needs (Ljubičić et al., 2020, Dykens & Lambert 2013). Given these findings, we anticipate that regular maternally-administered massage could reduce salivary cortisol in short-term bouts, which may lead to reduced psychological stress , anxiety, and depressive symptoms over time (Bigelow & Power 2020). Ultimately, improved parent mental health is associated with better infant gross motor and behavioral outcomes (Hofheimer et al., 2020, Kleine et al., 2020, de Cock et al., 2017). Additional research in larger, randomized cohorts is needed to support this preliminary evidence.

This study had multiple limitations. The modest sample size limited the statistical precision of our estimate of the effect of the intervention. Additionally, the laboratory test for salivary cortisol used in this study did not detect values below 50 ng/dL, so some changes may not have been detected, potentially leading to an underestimation of the true change in salivary cortisol for some individuals. Future research should aim to assess these changes in a larger sample with a more sensitive laboratory measure.

For parent saliva collection, we requested that parents not eat or drink 15 minutes prior to the scheduled session based on printed instructions on the saliva collection packet. The research assistant verified this prior to collection. We also recommended scheduling all massage sessions between 10:30 am and 1:30 pm to reduce the collection time window, but this was not feasible for 7 mothers. Regarding the additional collection recommendations found on the Salimetrics website (Salimetrics, n.d.), we did not ask participants to limit foods with high levels of sugar, acidity, or caffeine or refrain from smoking for 12 hours prior to collection, and we did not record whether parents had recently completed vigorous exercise or eaten a major meal. All of these variations in substance intake and timing of massage could interfere with the saliva immunoassay (Klein et al., 2010; Schwartz et al., 1998; Granger et al., 2007, 2009; Hibel et al., 2006, 2007; Kivlighan et al., 2006). The impact of these variations was potentially minimized, however, because our question was focused on pre- and post- differences salivary cortisol in response to an intervention, and because we were not examining group differences.

Additionally, our study did not use any additional measures of short-term stress, such as the State-Trait Anxiety Inventory, to coincide with the biological measure, which should be considered in future research (Spielberger et al., 1983). Lastly, consistent with previous studies (White-Traut et al., 2009), we were not able to assess salivary cortisol changes in infants because insufficient levels of saliva were collected using the sampling technique outlined by Salimetrics (Mörelius et al., 2012; Salimetrics, n.d.). The buccal swabs in the cortisol collection kits were designed for infants age 0–6 months, which could have impacted the effectiveness of use for infants less than term age (Salimetrics, n.d.). Prior studies investigating salivary cortisol changes in infants collected saliva over much longer periods of time by the nature of the intervention (ie. during skin-to-skin holding), which was not possible in this study because it would have required waking the infants at least 30 minutes prior to their care time (Vittner et al., 2018). Other methods and timing for cortisol collection should be considered in future studies.

Conclusion

In this study, infant massage was determined to be a safe, low-risk intervention for use with extremely preterm infants once they established the ability to maintain body temperature outside of the incubator. We found reduced cortisol levels in cortisol-responding parents after infant massage administration, indicating a biological decrease in stress, which supported our hypothesis. Future studies should investigate the role of diurnal fluctuations on salivary cortisol pre- and post- infant massage as well as more effective methods of salivary cortisol collection in preterm infants. While further powered studies examining the benefits of infant massage for parent mental health is warranted, this preliminary study supports integration of infant massage into clinical practice in neonatal intensive care units.

Figure 1:

TEMPO Study Procedures after Enrollment, through time of Salivary Cortisol Measurement. Infant massage education session highlighted.

Key Findings:

1. Physiological stress, as measured by salivary cortisol, was reduced after maternally-administered massage in extremely preterm infants in a small cohort of mothers.We found reduced cortisol levels in cortisol-responding parents after infant massage administration, indicating a physiological decrease in stress, which supported our hypothesis.

2. Parent-administered infant massage may provide a unique opportunity to combine the beneficial developmental effects of skin-to-skin contact at an age when preterm infant social behaviors are emerging, enhancing parent-infant attachment.

3. New methods to effectively measure and quantify biomarker changes in infants and parents should be explored in order to better understand the potential mechanisms by which infant massage intervention works.

Data sharing and availability statement:

Data available on request from the authors