Changes in Salivary Oxytocin Level of Term Pregnant Women after Aromatherapy Footbath for Spontaneous Labor Onset: A Non-Randomized Experimental Study.

BACKGROUND: Aromatherapy is usually used to stimulate labor. However, its specific physiological effects have been scarcely examined. We evaluated whether an aromatherapy footbath increases oxytocin levels in term pregnant women. METHODS: In this quasi-experimental study, low-risk term pregnant women in Japan underwent aromatherapy using a footbath (1) infused with clary sage and lavender essential oils, (2) infused with jasmine oil, or (3) with no infused oils (control group). The primary outcome was the salivary oxytocin level. The secondary outcomes were uterine contractions and cortisol levels. RESULTS: In the clary sage and lavender group (n = 28), the oxytocin level increased significantly after the footbath (p = 0.035). The jasmine group (n = 27) and control group (n = 27) exhibited trends toward a respective increase and decrease in the oxytocin level; however, the changes in the oxytocin levels between the clary sage and lavender group and the control group showed no significance difference. There were no significant differences in the changes in the uterine contractions and cortisol levels between the experiment and control groups. CONCLUSIONS: The changes in the oxytocin levels in the clary sage and lavender group did not differ significantly with those in the control group, possibly because of the small sample size. Further studies are required to examine the effects of repeated aromatherapy footbaths to stimulate labor.

Parental bonding in retrospect and adult attachment style: A comparative study between Spanish, Italian and Japanese cultures.

Attachment is an innate human relational mechanism that develops progressively from early childhood, influences individuals' representations and behaviors, shapes relationships, and affects the social and cultural environment. Parental bonding refers to the ability of parents to be emotionally and behaviorally available to the child during infancy. Attachment style refers to the individual's relational attitude in close relationships that influences adult love, bonding, handling relationships, and social exploration. The role of intergenerational, cultural and developmental factors influencing the relationship between the attachment style in adulthood and the parental bonding style recalled during childhood has been debated. This study explores the relationships between recalled parental bonding, adult attachment style, and cultural background in a sample of Spanish, Italian, and Japanese adults using a cross-sectional and cross-cultural design. For this purpose, the validated versions of the Experience in Close Relationship Scale and the Parental Bonding Instrument were administered to a non-clinical population of three hundred and five participants in the three countries. Results show that the most frequent adult attachment style is the secure style, followed by the dismissing-avoidant, the preoccupied, and the fearful-avoidant style. The dismissing-avoidant style was the most frequent insecure attachment style in the Japanese sample whereas the preoccupied style was the most frequent insecure attachment style in the Italians and Spaniards. Japanese are more anchored to the memory of maternal and paternal overprotection, which is related to more avoidance in actual close relationships. Spaniard's current relationships are mildly independent of recalled parental bonding, showing an association between lower current avoidance to primary parental care. In the Italian sample, there is no significant relationship between current adult close relationships and recalled parental bonding. These results suggest that different cultural models influence adult attachment representations differently, in terms of the weight placed on attachment-related avoidance, attachment-related anxiety, care, and overprotection in infant and adult relationships.

Prediction of autistic tendencies at 18 months of age via markerless video analysis of spontaneous body movements in 4-month-old infants.

Early intervention is now considered the core treatment strategy for autism spectrum disorders (ASD). Thus, it is of significant clinical importance to establish a screening tool for the early detection of ASD in infants. To achieve this goal, in a longitudinal design, we analyzed spontaneous bodily movements of 4-month-old infants from general population and assessed their ASD-like behaviors at 18 months of age. A total of 26 movement features were calculated from video-recorded bodily movements of infants at 4 months of age. Their risk of ASD was assessed at 18 months of age with the Modified Checklist for Autism in Toddlerhood, a widely used screening questionnaire. Infants at high risk for ASD at 18 months of age exhibited less rhythmic and weaker bodily movement patterns at 4 months of age than low-risk infants. When the observed bodily movement patterns were submitted to a machine learning-based analysis, linear and non-linear classifiers successfully predicted ASD-like behavior at 18 months of age based on the bodily movement patterns at 4 months of age, at the level acceptable for practical use. This study analyzed the relationship between spontaneous bodily movements at 4 months of age and the ASD risk at 18 months of age. Experimental results suggested the utility of the proposed method for the early screening of infants at risk for ASD. We revealed that the signs of ASD risk could be detected as early as 4 months after birth, by focusing on the infant's spontaneous bodily movements.

The Interaction Effect of Parental Rejection and Oxytocin Receptor Gene Polymorphism on Depression: A Cross-Cultural Study in Non-Clinical Samples.

Parental rejection has been consistently empirically implicated in a wide array of developmental, behavioural and psychological problems worldwide. However, the interaction effect between parental rejection in childhood and the oxytocin receptor genotype on psychological adjustment has yet to be investigated. The present study aimed to investigate gene-environment interaction effects between parental rejection (maternal and paternal) and oxytocin receptor (OXTR) gene polymorphisms (rs53576 and rs2254298) on depressive symptoms in adults in different cultural contexts. Adults from Italy and Japan (N = 133, age = 18-27 years, females = 68) were preliminarily genotyped and then completed the Parental Acceptance-Rejection Questionnaire for mothers and fathers and the Beck Depression Inventory. Hierarchical multiple regression analysis showed that paternal rejection was related to self-reported depression and that the effect of parental rejection was moderated by OXTR gene polymorphisms and nationality. Among Italians, OXTR rs2254298 A-carriers showed resilience to negative early parental care, whereas among Japanese, OXTR rs53576 non-A-carriers showed resistance to negative early paternal care. These findings align with expected relations between perceived acceptance-rejection and an individual's psychological adjustment, as proposed by interpersonal acceptance-rejection theory, and indicate the need for future studies adopting a multicultural and multilevel approach to better understand how the effects of parental rejection extend into adulthood.

Cellular senescence and its impact on the circadian clock.

Ageing is one of the greatest risk factors for chronic non-communicable diseases, and cellular senescence is one of the major causes of ageing and age-related diseases. The persistent presence of senescent cells in late life seems to cause disarray in a tissue-specific manner. Ageing disrupts the circadian clock system, which results in the development of many age-related diseases such as metabolic syndrome, cancer, cardiac diseases and sleep disorders and an increased susceptibility to infections. In this review, we first discuss cellular senescence and some of its basic characteristics and detrimental roles. Then, we discuss a relatively unexplored topic on the link between cellular senescence and the circadian clock and attempt to determine whether cellular senescence could be the underlying factor for circadian clock disruption.

Exploration of the Spanish Version of the Attachment Style Questionnaire: A Comparative Study between Spanish, Italian, and Japanese Culture.

Nowadays, there are several human attachment measures, most in the form of questionnaires that assess adult attachment styles. This study investigates the use of Feeney, Noller, Hanrahan, Sperling and Berman's five-factors Attachment Style Questionnaire (ASQ, 1994), based on Bartholomew's four-factors model (1991), and Hazan and Shaver's three-factors model (1987). Nevertheless, no robust study has explored the ASQ questionnaire in Spanish compared to other cultures, such as Italian and Japanese. Therefore, the linguistic translation of the Spanish version of the ASQ was performed, based on the back-translation methodology. The results indicate that 5-factors ASQ Spanish version explains 43.67% of the variance, similar to the original English-Australian ASQ version. The Italian and Japanese versions explain 49.37% and 52.27% of the variance, respectively. No age correlation for any ASQ factors in the Japanese sample was found; meanwhile, the Spanish and Italian cultures showed a positive correlation with age and "Confidence" and negative correlation with age and "Relationships as Secondary" ASQ factors. Some transcultural differences and possible research approaches are addressed.

Distribution of dietary protein intake in daily meals influences skeletal muscle hypertrophy via the muscle clock.

The meal distribution of proteins throughout the day is usually skewed. However, its physiological implications and the effects of better protein distribution on muscle volume are largely unknown. Here, using the two-meals-per-day feeding model, we find that protein intake at the early active phase promotes overloading-induced muscle hypertrophy, in a manner dependent on the local muscle clock. Mice fed branched-chain amino acid (BCAA)-supplemented diets at the early active phase demonstrate skeletal muscle hypertrophy. However, distribution-dependent effects are not observed in ClockΔ19 or muscle-specific Bmal1 knockout mice. Additionally, we examined the relationship between the distribution of proteins in meals and muscle functions, such as skeletal muscle index and grip strength in humans. Higher muscle functions were observed in subjects who ingested dietary proteins mainly at breakfast than at dinner. These data suggest that protein intake at breakfast may be better for the maintenance of skeletal muscle mass.

Attenuated SIRT1 Activity Leads to PER2 Cytoplasmic Localization and Dampens the Amplitude of Bmal1 Promoter-Driven Circadian Oscillation.

The circadian clock possesses robust systems to maintain the rhythm approximately 24 h, from cellular to organismal levels, whereas aging is known to be one of the risk factors linked to the alternation of circadian physiology and behavior. The amount of many metabolites in the cells/body is altered with the aging process, and the most prominent metabolite among them is the oxidized form of nicotinamide adenine dinucleotide (NAD+), which is associated with posttranslational modifications of acetylation and poly-ADP-ribosylation status of circadian clock proteins and decreases with aging. However, how low NAD+ condition in cells, which mimics aged or pathophysiological conditions, affects the circadian clock is largely unknown. Here, we show that low NAD+ in cultured cells promotes PER2 to be retained in the cytoplasm through the NAD+/SIRT1 axis, which leads to the attenuated amplitude of Bmal1 promoter-driven luciferase oscillation. We found that, among the core clock proteins, PER2 is mainly affected in its subcellular localization by NAD+ amount, and a higher cytoplasmic PER2 localization was observed under low NAD+ condition. We further found that NAD+-dependent deacetylase SIRT1 is the regulator of PER2 subcellular localization. Thus, we anticipate that the altered PER2 subcellular localization by low NAD+ is one of the complex changes that occurs in the aged circadian clock.

Chrono-Nutrition Has Potential in Preventing Age-Related Muscle Loss and Dysfunction.

The mammalian circadian clock systems regulate the day-night variation of several physiological functions such as the sleep/wake cycle and core body temperature. Disturbance in the circadian clock due to shiftwork and chronic jetlag is related to the risk of several disorders such as metabolic syndrome and cancer. Recently, it has been thought that shiftwork increases the risk of sarcopenia which is characterized by age-related decline of muscle mass and its dysfunctions including muscle strength and/or physical performance. First, we summarize the association between circadian rhythm and the occurrence of sarcopenia and discuss its mechanistic insight by focusing on the muscle function and molecular clock gene in knockout or mutant mice. The clock gene knockout or mutant mice showed early aging phenotypes, including low survival rate and muscle loss. It suggests that improvement in the disturbance of the circadian clock plays an important role in the aging process of healthy muscles. Nutritional intake has the potential to augment muscle growth and entrain the peripheral clock. Second, we discuss the potential of chrono-nutrition in preventing aging-related muscle loss and dysfunction. We also focus on the effects of time-restricted feeding (TRF) and the distribution of protein intake across three meals.

The Recognition of Cross-Cultural Emotional Faces Is Affected by Intensity and Ethnicity in a Japanese Sample.

Human faces convey a range of emotions and psychobiological signals that support social interactions. Multiple factors potentially mediate the facial expressions of emotions across cultures. To further determine the mechanisms underlying human emotion recognition in a complex and ecological environment, we hypothesized that both behavioral and neurophysiological measures would be influenced by stimuli ethnicity (Japanese, Caucasian) in the context of ambiguous emotional expressions (mid-happy, angry). We assessed the neurophysiological and behavioral responses of neurotypical Japanese adults (N = 27, 13 males) involved in a facial expression recognition task. Results uncover an interaction between universal and culturally-driven mechanisms. No differences in behavioral responses are found between male and female participants, male and female faces, and neutral Japanese versus Caucasian faces. However, Caucasian ambiguous emotional expressions which require more energy-consuming processing, as highlighted by neurophysiological results of the Arousal Index, were judged more accurately than Japanese ones. Additionally, a differential Frontal Asymmetry Index in neuronal activation, the signature of an approach versus avoidance response, is found in male participants according to the gender and emotional valence of the stimuli.

Changes in the cortisol and oxytocin levels of first-time pregnant women during interaction with an infant: a randomized controlled trial.

BACKGROUND: During pregnancy, physiological, psychological, and social changes affect pregnant women's childcare anxiety and childrearing behavior. However, there are scarce reports on hormonal evaluation related to such anxiety and behavior. Herein, we evaluated changes in salivary cortisol (primary outcome) and oxytocin (secondary outcome) levels of first-time pregnant women when interacting with an infant and discussed the relation of these changes to the women's stress level. METHODS: This was a two-arm randomized controlled trial. Participants were randomly assigned using a web-based randomization system. The experimental group involved interaction with an infant for 30 min. The control group involved watching a DVD movie of an infant for 30 min. Saliva samples were collected at preintervention and postintervention. Saliva samples were assayed, and all data were compared between and within the groups using independent t-test and paired t-test with a two-sided 5% significance level. This study was approved by the Research Ethics Committee of St. Luke's International University. RESULTS: A total of 102 women were randomly assigned to the experimental (n = 51) and control (n = 51) groups. Finally, 38 women in the experimental group and 42 women in the control group were analyzed. The salivary cortisol level significantly decreased after the interventions in both groups (t = 4.57, p = 0.00; t = 5.01, p = 0.00). However, there were no significant differences in the salivary cortisol (t = 0.349, p = 0.73) and oxytocin (t = - 1.945, p = 0.58) levels between the two groups. CONCLUSIONS: The salivary cortisol level of first-time pregnant women significantly decreased in the experimental and control groups postintervention, although no significant difference was found between the two groups. Such decrease indicates stress reduction and release among these women. The absence of a significant increase in salivary oxytocin level in both groups may be related to the limitations of an insufficient number of samples that could be analyzed owing to the small saliva volume in some samples and the lack of adequate tactile stimulation of the intervention protocol. These results and procedural limitations provide useful insights into approaching subsequent studies aiming at continuously optimizing detection procedures. TRIAL REGISTRATION: UMIN000028471 (Clinical Trials Registry of University Hospital Information Network. July 31, 2017- Retrospectively registered.

Cellular Senescence Triggers Altered Circadian Clocks With a Prolonged Period and Delayed Phases.

Senescent cells, which show the permanent growth arrest in response to various forms of stress, accumulate in the body with the progression of age, and are associated with aging and age-associated diseases. Although the senescent cells are growth arrested, they still demonstrate high metabolic rate and altered gene expressions, indicating that senescent cells are still active. We recently showed that the circadian clock properties, namely phase and period of the cells, are altered with the establishment of replicative senescence. However, whether cellular senescence triggers the alteration of circadian clock properties in the cells is still unknown. In this study we show that the oxidative stress-induced premature senescence induces the alterations of the circadian clock, similar to the phenotypes of the replicative senescent cells. We found that the oxidative stress-induced premature senescent cells display the prolonged period and delayed phases. In addition, the magnitude of these changes intensified over time, indicating that cellular senescence changes the circadian clock properties. Our current results corroborate with our previous findings and further confirm that cellular senescence induces altered circadian clock properties, irrespective of the replicative senescence or the stress-induced premature senescence.

Effects of epidural anesthesia on postpartum maternity blues and fatigue and its relation to changes in oxytocin.

AIMS: This study aimed to clarify (a) the association of the delivery mode (i.e., epidural anesthesia or no epidural) with women's changes in longitudinal salivary oxytocin (OT) levels from late pregnancy to early postpartum, and (b) the association of these changes with postpartum maternity blues (MB) and fatigue. METHODS: We used a longitudinal observational design. We performed measurements of the saliva samples at four measurement points: (a) 36-37 gestational weeks, (b) 38-39 gestational weeks, (c) 1-2 days after birth, and (d) 4-5 days after birth. The inclusion criterion was low-risk primiparous women who were planning to have vaginal delivery. We used Stein's MB scale to evaluate postpartum data and a visual analog scale to examine "postpartum fatigue". We determined the association between the MB/fatigue scores and the changes in the OT levels by Spearman's rank correlation coefficient. RESULTS: There were 29 women who delivered with epidural anesthesia and 29 women who did not. A significantly higher mean salivary OT level was observed in the women with epidural anesthesia at 1-2 days after birth than at 36-37 gestational weeks. The mean OT level at 4-5 days postpartum was significantly lower than that at 1-2 days postpartum. The correlation of the MB score with the salivary OT level at 4-5 days postpartum was ρ = -0.33, p = .01. CONCLUSIONS: Early postpartum OT level decreased with epidural anesthesia and showed a negative correlation with postpartum MB and fatigue. Healthcare providers should recognize that women who had epidural anesthesia need specific supportive care.

Olfactory Exposure to ß-Caryophyllene Increases Testosterone Levels in Women's Saliva.

INTRODUCTION: From previous studies, we hypothesized that olfactory exposure to ß-caryophyllene stimulates women's libido. However, Japan's sex culture is so closed that it is difficult to test this possibility without accumulating scientific evidence. Therefore, it is necessary to measure the concentration of sex-related hormones in saliva, an experimental technique that is relatively easy to obtain research permission, and to obtain a scientific basis to convince ethics committee reviewers. AIM: The aim of this study is to investigate whether ß-caryophyllene increases salivary testosterone concentrations associated with libido and vaginal sensation during intercourse in women. METHODS: 19 women in the follicular phase of the menstrual cycle participated in the study. The subjects then sat in front of the odor exposure device we had created. Each subject was exposed to dipropylene glycol for 20 minutes, followed by 3% ß-caryophyllene for 20 minutes. Saliva was collected 4 times: before and after control exposure, and before and after ß-caryophyllene exposure. MAIN OUTCOME MEASURE: Salivary testosterone and estrogen concentrations were measured with a competition ELISA. RESULTS: ß-caryophyllene significantly increased the salivary concentration of testosterone (control vs ß-caryophyllene; 0.97 ± 0.05 vs 1.13 ± 0.03, P = .00, 95% confidence interval of control: 0.84-1.09, 95% confidence interval of ß-caryophyllene: 1.04-1.20) but not estrogen (control vs ß-caryophyllene; 1.05 ± 0.03 vs 1.07 ± 0.04, P = .69, 95% confidence interval of control: 0.96-1.12, 95% confidence interval of ß-caryophyllene: 0.98-1.15). STRENGTHS & LIMITATIONS: The personal preferences of the subjects and the order of exposure may have affected the results. CONCLUSION: ß-caryophyllene may be a remedy with fewer side effects for women with decreased libido. We believe that ß-caryophyllene may be a remedy for women with decreased libido. However, this hypothesis must be tested by further clinical studies. Wataru Tarumi, Kazuyuki Shinohara. Olfactory Exposure to ß-Caryophyllene Increases Testosterone Levels in Women's Saliva. J Sex Med 2020;8:525-531.

Women's body odour during the ovulatory phase modulates testosterone and cortisol levels in men.

A growing body of evidence suggests that men may perceive women's bodily odour to be more attractive during the high-fertility ovulatory phase than during other phases in the menstrual cycle. In particular, women's bodily odour may influence important aspects of male mating behaviour, but the precise nature of this phenomena remains to be elucidated. Twenty-six men and five women participated in the study. Each woman wore a cotton T-shirt during the night for 3 days during the ovulatory phase, after which the regions of the T-shirt that had been in contact with the woman's chest, armpits, and back, were cut out of the garment. We evaluated the changes in testosterone and cortisol levels in the saliva of men who smelled these cloth pieces. The odour emitted from the backs of women in the ovulatory phase was found to increase testosterone secretion in men, whereas the odour emitted from the chests of women in the ovulatory phase reduced cortisol secretion in men. These results suggest that the odour of specific body parts of women modulate unconscious physiological reactions in men.

The Effects of Essential Oil on Salivary Oxytocin Concentration in Postmenopausal Women.

Objectives: The aim of this study was to find essential oils that have increased the oxytocin concentration in postmenopausal women. Methods: Fifteen postmenopausal women participated in this study and the effects of 10 different essential oils were investigated. The essential oils included rose otto, sweet orange, lavender, neroli, frankincense, jasmine absolute, ylang ylang, roman chamomile, clary sage, and Indian sandalwood. The subjects were exposed to the control first for 20 min, followed by exposure to an essential oil for 20 min. Each subject received exposure to only a single kind of essential oil per day. Saliva was collected four times for each patient: immediately before and immediately after control exposure, and immediately before and immediately after essential oil exposure. The oxytocin concentration in the saliva was measured using a competitive ELISA kit. Results: The results showed that salivary oxytocin concentrations increased significantly more after exposure to lavender, neroli, jasmine absolute, roman chamomile, clary sage, and Indian sandalwood than after exposure to the control odor. Conclusions: The aroma of certain essential oils may elicit increased secretion of oxytocin in postmenopausal women. This study suggests that olfactory stimulation with any of a number of essential oils increases salivary oxytocin concentrations, which may inhibit aging-induced reduction in muscle mass and function in women.

Lack of implicit visual perspective taking in adult males with autism spectrum disorders.

BACKGROUND: Some theorists have suggested that the ability of visual perspective-taking (VPT) constitutes a rudimentary process of social cognition, and as such, the ability of VPT in people with autism spectrum disorder (ASD) has been the focus of intensive research. AIM: The present study investigated whether adult males with ASD show signs of implicit VPT in first-level VPT tasks, in which participants were required to judge whether a target object can be seen from another's perspective, even when they are not explicitly required to take another's perspective. METHODS AND PROCEDURES: We examined whether the information from another's visual perspective interferes with visual processing from the participant's own perspective ("altercentric interference") using the reaction time as the main performance indicator in adult males with or without ASD. Eye movement patterns during VPT were analyzed for some participants. OUTCOMES AND RESULTS: The results revealed signs of altercentric interference in neurotypical adults, but not in adult males with ASD. CONCLUSIONS AND IMPLICATIONS: The results indicate the possibility that people with ASD may rely on a different strategy than neurotypical adults in completing a first-level VPT task.

Inaudible components of the human infant cry influence haemodynamic responses in the breast region of mothers.

Distress vocalizations are fundamental for survival, and both sonic and ultrasonic components of such vocalizations are preserved phylogenetically among many mammals. On this basis, we hypothesized that ultrasonic inaudible components of the acoustic signal might play a heretofore hidden role in humans as well. By investigating the human distress vocalization (infant cry), here we show that, similar to other species, the human infant cry contains ultrasonic components that modulate haemodynamic responses in mothers, without the mother being consciously aware of those modulations. In two studies, we measured the haemodynamic activity in the breasts of mothers while they were exposed to the ultrasonic components of infant cries. Although mothers were not aware of ultrasounds, the presence of the ultrasounds in combination with the audible components increased oxygenated haemoglobin concentration in the mothers' breast region. This modulation was observed only when the body surface was exposed to the ultrasonic components. These findings provide the first evidence indicating that the ultrasonic components of the acoustic signal play a role in human mother-infant interaction.

Low Salivary Testosterone Level Is Associated With Efficient Attention Holding by Self Face in Women.

Capacity to recognize one's own face (hereinafter referred to as self face) is a fundamental component of various domains of social cognition such as empathy in humans. Previous research has demonstrated that a high level of androgen suppresses empathic behavior and social brain function. Taking these into consideration, we hypothesized that people with high androgen level show reduced response to self face. The present study examined this hypothesis by investigating the association between attentiveness towards self face, as assessed by a psychophysiological experiment, and salivary testosterone concentration. The attentional responses to self face was measured by a modified Go/NoGo task. In this task, self face or unfamiliar other's face was presented simultaneously with Go or NoGo signal. In go trials, participants had to divert their attention from the face to a peripheral target. The reaction time (RT) for peripheral target detection in each condition was measured. In addition to behavioral data, saliva samples were collected to assay salivary testosterone concentration. The index of potency of self face to hold viewer's attention that was computed based on RT data was regressed against salivary testosterone concentration in men and women separately. The analyses revealed that self face holds visuospatial attention more effectively in women with low than high salivary testosterone level, but no such trend was observed in men. This pattern of results indicates that low testosterone level is associated with a pronounced response to self face as we hypothesized and raises the possibility that multiple aspects of self-face processing are under the influence of endocrinological function.

Oxytocin levels in low-risk primiparas following breast stimulation for spontaneous onset of labor: a quasi-experimental study.

BACKGROUND: Breast stimulation is performed to self-induce labor. However, there are apparently no reports on hormonal evaluation during stimulation for consecutive days in relation to induction effect. We evaluated the salivary oxytocin level following 3 consecutive days of own breast stimulation for 1 h each day compared with no breast stimulation. METHODS: We used a quasi-experimental design. The participants were low-risk primiparas between 38 and 39 gestational weeks. Eight saliva samples per participant were collected at preintervention and 30, 60, and 75 min postintervention on the first and third days. The primary outcome was change in the salivary oxytocin level on the third day after 3 consecutive days of breast stimulation for 1 h each day compared with no breast stimulation. The secondary outcomes were the rate of spontaneous labor onset and negative events including uterine hyperstimulation and abnormal fetal heart rate. RESULTS: Between February and September 2016, 42 women were enrolled into the intervention group (n = 22) or control group (n = 20). As there were differences in the basal oxytocin levels between the 2 groups, to estimate the change in the oxytocin level from baseline, we used a linear mixed model with a first-order autoregressive (AR1) covariance structure. The dependent variable was change in the oxytocin level from baseline. The independent variables were gestational weeks on the first day of intervention, age, education, rs53576 and rs2254298, group, time point, and interaction of group and time. After Bonferroni correction, the estimated change in the mean oxytocin level at 30 min on the third day was significantly higher in the intervention group (M = 20.2 pg/mL, SE = 26.2) than in the control group (M = - 44.4 pg/mL, SE = 27.3; p = 0.018). There was no significant difference in the rate of spontaneous labor onset. Although there were no adverse events during delivery, uterine tachysystole occurred in 1 case during the intervention. CONCLUSIONS: The estimated change in the mean oxytocin level was significantly higher 30 min after breast stimulation on the third day. Thus, consecutive breast stimulation increased the salivary oxytocin level. Repeated stimulations likely increase the oxytocin level. TRIAL REGISTRATION: UMIN000020797 (University Hospital Medical Information Network; Prospective trial registered: January 29, 2016).