Introduction

Moderate to late preterm (MLPT) neonates, including infants born between 32+0 and 33+6 (moderate) and 340 to 36+6 (late) weeks of gestation, often require active resuscitation. Therefore, interventions that favor postnatal stabilization are of particular interest. In high-income countries (HIC), MLPT accounts for 71.8% of all preterm deliveries [1].

Kangaroo mother care (KMC) is defined as the direct interaction between the newborn and the naked torso of the mother after birth. KMC enhances infant’s temperature regulation, promotes breastfeeding, and fosters a strong bond between mother and child. It is prioritized in low- and middle-income countries (LMIC) as a key strategy to enhance neonatal health outcomes and increase survival rates, particularly for low birth-weight (LBW) infants [2, 3]. The physiological mechanism underlying KMC involves skin-to-skin contact that activates thermoregulatory and neuroendocrine pathways, including the release of oxytocin and modulation of the autonomic nervous system. These responses help stabilize vital parameters such as heart rate (HR) and oxygen saturation (SpO₂) in preterm and term newborns [4], and have been associated with reduced mortality at 28 days when implemented immediately after birth [3].

Delayed cord clamping (DCC), defined as delaying at least 60 s before clamping the umbilical cord, has been shown to facilitate cardiopulmonary transition at birth. Placental transfusion increases blood volume, enhances pulmonary gas exchange, and stabilizes HR during the immediate postnatal period [5,6,7].

We hypothesized that in MPLTs, the simultaneous combination of iKMC and DCC would enhance earlier stabilization of SpO2 and HR compared with those not receiving iKMC.

Population & methodos

Study design

Post-hoc analysis from an observational cohort study conducted at the Hospital Universitario y Politécnico La Fe (Valencia, Spain) [7].

SpO2, HR, time of DCC, and iKMC time during stabilization were recorded in MLPT infants born by vaginal delivery or cesarean section after an uncomplicated pregnancy that did not require stabilization maneuvers in the delivery room (DR). GA was defined according to the criteria of the Spanish Society of Obstetrics and Gynecology (SEGO) [8]. All neonates underwent skin stimulation to improve spontaneous breathing [9].

Ethics

The study was approved by the Medical Research Ethics Committee (ID = 2021-275-1). Parents/legal guardians signed the informed consent.

Population, study interventions, and monitoring

Inclusion criteria were MLPT (320–36⁶ weeks) born after uncomplicated pregnancies, who did not require stabilization maneuvers in the delivery room. Exclusion criteria included major congenital malformations, need for resuscitation, and/or maternal contraindications for iKMC. The comparison was made between infants who received iKMC and those who did not (non-iKMC), to assess early physiological adaptation. Mode of delivery (vaginal or cesarean) was considered one of the contextual factors influencing iKMC implementation according to institutional protocols.

Midwives and neonatal nurses handled all the infants in the DR. Preductal SpO2 and HR were retrieved for 10 min after fetal expulsion and stored [7]. Cord clamping was delayed for ≥ 60 s according to the Spanish guidelines [8]. iKMC was offered to clinically stable infants, following established criteria for stability (Apgar ≥8 at 1 min, no need for respiratory support). Cesarean deliveries were performed according to obstetric indications, independent of neonatal status, and the decision for iKMC followed standard clinical procedures. Infants requiring stabilization maneuvers were excluded from iKMC.

In vaginal deliveries, the newborn was placed on the mother’s lower abdomen or thighs, approximately at the level of the placenta, with the cord unclamped for ≥ 60 s and gentle tactile stimulation to encourage spontaneous breathing. In cesarean deliveries, the newborn was placed on the mother’s thighs, covered with pre-warmed cloths, maintaining the cord intact for the same period. After DCC, clinically stable newborns were transferred skin-to-skin to the mother’s chest to initiate iKMC.

The investigators were not involved in clinical decisions or interventions regarding the delivery and postnatal stabilization of the newborn. Monitor alarms were not silenced during resuscitation procedures. All infants requiring stabilization maneuvers were excluded from the study.

HR and preductal SpO₂ were continuously measured using a Masimo SET Masimo M-LNCS Neo sensor (Low Noise Cabled Sensor, Irvine, CA) placed on the right hand/wrist and connected to the Masimo Rad-97 Pulse CO-Oximeter®. The sensor was applied before connection to improve the reliability and speed of displayed data. Measurements were recorded at 2-second intervals with maximum sensitivity (HR sensitivity: 3 bpm for a 25–240 bpm range; SpO₂ sensitivity: 3% for a 60–80% range). All data were exported as .csv files for subsequent analysis, enabling precise assessment of neonatal physiological parameters during the first 10 min after birth.

Statistical analysis

The data were summarized as mean (standard deviation, SD) and median (first and third quartiles) for continuous variables, and as relative and absolute frequencies for categorical variables. The statistical analysis was divided into two parts:

First, SpO2 and HR percentiles were calculated using generalized least squares regression with the rms R package (v 5.4-1, R Foundation for Statistical Computing, Vienna, Austria) [10]. Relevant variables such as gestational age, sex, iKMC, and delivery mode (vaginal/C-section) were included in the model. Additionally, a within-group correlation structure was introduced to correct for non-independent observations. SpO2 values equal to 100 were changed to 99.9 and divided by 100 for a logit transformation. Nonlinear relationships between time (in minutes) and the response variables were modeled using natural splines. Percentiles were calculated using the quantile function for the standard normal distribution. Each model’s estimated residual standard error was multiplied by the corresponding value of a standard normal distribution for the required quantile and added to the predicted mean. Logit-transformed SpO2 percentile values were back-transformed to display the results.

Second, to compare percentiles based on whether iKMC had been performed, the skewness-median-coefficient of variation (LMS) method described by Cole et al. [11] was applied. Results were fitted using the gamlss R package (v 5.1-6). Statistical analyses were conducted using R statistical software (v 3.6.1).

Results

A total of 96 preterm neonates with a median gestational age of 35 weeks (34–36) and a mean birth weight of 2294.8 ± 397 g were included in the study. Table 1 provides clinical information on the mothers and neonates. The median DCC time was 70 s. Baseline sociodemographic and perinatal characteristics the iKMC and non-iKMC groups are shown in the Supplementary Table 1. No significant differences were assessed between the study groups.

Table 1 Characteristics of the mother, newborn, delivery, and clinical parameters.
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Table 2 shows the values of SpO2 for each time point. SpO₂ was 8% higher in the iKMC than in the non-iKMC group across all time points; however, this difference did not reach statistical significance (p = 0.082). At 120 s of life, neonates in the iKMC group had a mean SpO₂ of 76.3% (95% CI: 65.4–84.2) compared to 71% (95% CI: 63.2–77.7) in the non-iKMC group. This trend persisted in subsequent measurements, reaching a mean SpO₂ of 88.9 (95% CI: 87–92) at 300 s in the iKMC group, compared to 92% (95% CI: 87.5–95) in the non-iKMC groups. Figure 1 depicts the time-dependent progression of SpO₂ in both groups during the first minutes of life.

Fig. 1: Oxygen saturation (SpO₂, %) during the first 10 min after birth in neonates receiving immediate Kangaroo Mother Care (iKMC, red) compared with those without iKMC (black).
Fig. 1: Oxygen saturation (SpO₂, %) during the first 10 min after birth in neonates receiving immediate Kangaroo Mother Care (iKMC, red) compared with those without iKMC (black).The alternative text for this image may have been generated using AI.
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The x-axis represents time (minutes) and the y-axis oxygen saturation (%). Solid lines indicate median values, and dashed lines represent the 3rd, 50th, and 97th percentiles. Neonates with iKMC showed consistently higher SpO₂ values throughout this period.

Table 2 Median peripheral oxygen saturation (SpO₂) in moderate and late preterm (MLPT) neonates with and without immediate Kangaroo Mother Care (iKMC) during the first 10 min of life.
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Table 3 shows HR values at different time points. At 120 s after birth, the iKMC group had a mean HR of 102.2 bpm (95% CI: 88.9–117.5) compared to 90.1 bpm (95% CI: 87.7–98.5) in the non-iKMC group. At 300 s after birth, the iKMC group showed a mean HR of 135.2 bpm (95% CI: 120.7–149.7) compared to 120 bpm mean in the non-iKMC group (95% CI: 109–130.3). HR was consistently and significantly (p = 0.013) higher in the iKMC group throughout the study.

Table 3 Median heart rate (HR) in moderate and late preterm (MLPT) neonates with and without immediate Kangaroo Mother Care (iKMC) during the first 10 min of life.
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Figure 2 depicts evolving HR in the first minutes after birth. Statistically significant differences (p = 0.013) between iKMC and non-iKMC groups were assessed, with values approximately 14% higher in neonates who received iKMC.

Fig. 2: Heart rate (HR, beats per minute) during the first 10 min after birth in neonates with immediate Kangaroo Mother Care (iKMC, red) compared with those without iKMC (black), following delayed cord clamping.
Fig. 2: Heart rate (HR, beats per minute) during the first 10 min after birth in neonates with immediate Kangaroo Mother Care (iKMC, red) compared with those without iKMC (black), following delayed cord clamping.The alternative text for this image may have been generated using AI.
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The x-axis represents time (minutes) and the y-axis heart rate (beats per minute). Solid lines indicate median values, and dashed lines represent the 3rd, 50th, and 97th percentiles.

The statistical analysis included key variables such as gestational age, type of delivery, sex, umbilical artery pH at birth, neonatal weight and adjustments made in the SpO2 analysis. These methodological controls aimed to ensure that the physiological differences between groups could be attributed to the intervention and not to the baseline characteristics of delivery-related factors.

Table 4 informs on the body temperature in both groups at different timings. At 2–3 min of life, the iKMC group had a significantly higher mean temperature (36.1 ± 1 °C) compared with the non-iKMC group (35.8 ± 1 °C; p = 0.041). This difference increased at 5 min after birth (iKMC vs. non-iKMC: 36.4 ± 0.60 °C vs. 36.1 ± 0.7 °C; p = 0.018), and reach a peak at 10 min after birth (36.6 ± 0.5 °C vs. 36.3 ± 0.7 °C; p = 0.003). At the time of protocol entry or termination, the iKMC-exposed group maintained a significant thermal advantage (36.6 ± 0.5 °C vs. 36.3 ± 0.5 °C; p = 0.009).

Table 4 Neonatal body temperatures in moderate and late preterm (MLPT) neonates with and without immediate Kangaroo Mother Care (iKMC) at different time points after birth.
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Discussion

MLPT infants subjected to DCC plus iKMC achieved physiologic HR and SpO2 earlier than those with delayed KMC (non-iKMC group). These findings suggest that the combination of iKMC and DCC contributes to improved cardiovascular and respiratory adaptation in the transition to extrauterine life, in line with previous studies that have documented the physiological benefits of these interventions in vulnerable neonates [3, 12, 13].

Although our results showed a 14% higher heart rate (HR) in neonates receiving iKMC, this finding should be interpreted within the hemodynamic context of birth transition. In the third trimester, fetal HR typically ranges between 120 and 160 bpm, reflecting the high sympathetic tone of intrauterine life. From this perspective, the increased HR observed in the iKMC group may indicate a more physiologic transition from fetal to extrauterine circulation. iKMC contact may contribute to this process by reducing external stressors and mimicking the uterine thermal, tactile, and olfactory environment. Further studies, including autonomic markers such as HR variability or stress-related biomarkers, are needed to validate this interpretation.

The autonomic nervous system plays a key role in the fetal-to-neonatal transition, influencing HR regulation and oxygenation. Previous research has shown that iKMC modulates autonomic activity, promoting greater sympathetic-parasympathetic balance and reducing physiological stress in the neonate [14, 15]. In addition, KMC has been documented to enhance central nervous system maturation, which promotes HR regulation and cardiorespiratory stability in preterm and low birth weight neonates [16, 17]. An observational study showed that iKMC significantly reduced SpO2 and HR variability, compared to incubator care. In addition, KMC accelerates the maturation of vagal tone and improves state organization, suggesting faster maturation of the autonomic system [18].

DCC optimizes placental transfusion, increasing blood volume and improving oxygenation during the first minutes of life. A recent study by Padilla et al. (2021) [5] demonstrated that DCC is associated with higher SpO₂ levels and faster stabilization of HR, reducing episodes of bradycardia and tachycardia in term neonates.

Our data align with previous findings by Ashish et al. in neonates ≥33 weeks, where DCC was associated with higher SpO₂ values during early postnatal life [19]. In our cohort, a trend toward improved oxygenation was observed in iKMC + DCC infants although it didn’t reach statistical significance

iKMC contact improves thermoregulation and reduces temperature variability in preterm neonates [17, 19,20,21]. In our cohort, neonates exposed to iKMC showed significantly higher temperatures at all measured intervals, with the most pronounced difference observed at 10 min postpartum (+0.32 °C, *p* = 0.003).

The study has several limitations. HR during the fetal-to-neonatal transition was measured using pulse oximetry, a technique widely used in clinical practice because of its availability and ease of application. However, several studies have highlighted the limitations of this method, especially in the first minutes of life when it can experience delays in obtaining a stable signal and tends to underestimate the actual HR [22, 23]. In contrast, electrocardiography (EKG) provides a more accurate and faster HR signal, crucial for timely clinical decision-making during neonatal resuscitation [24, 25]. Recent literature supports the superiority of EKG over pulse oximetry for detecting bradycardia, particularly in preterm neonates [22], and suggests that using both technologies together significantly improves accuracy in hemodynamic monitoring [24, 25]. Consistent with these recommendations, phase II of the study has incorporated EKG monitoring to assess HR during neonatal transition, aiming to align the methodology with the latest scientific evidence and improve the accuracy of cardiovascular monitoring. Additionally, the generalizability of our findings is limited because infants who required resuscitation or advanced stabilization at birth were excluded [26,27,28]. Therefore, our results apply specifically to clinically stable moderate and late preterm neonates born after uncomplicated pregnancies. Future studies should include a broader spectrum of MLPT infants, including those requiring stabilization, to better assess the effects of iKMC and delayed cord clamping across the full range of clinical presentations.

Conclusions

Combining iKMC and DCC promotes hemodynamic stability during fetal-to-neonatal transition in MPLT infants. In our cohort, iKMC was associated with a significantly higher HR and earlies achievement of a stable SpO2 in the first minutes after birth. These findings underscore potential short-term physiological benefits of applying both interventions simultaneously. Further research is necessary to evaluate their long-term clinical effects and applicability in different delivery settings. applicability to neonates requiring stabilization maneuvers.