Physiological vital sign differences between well newborns greater than 34 weeks gestation: a pilot study

Background: Newborns have their vital signs measured as part of routine care. However, there is inconsistency in accepted physiological ranges for well newborns beyond the post-delivery stabilisation period which has implications for the identification of illness. Objective: To explore differences in physiological vital signs between three gestational age groups: late preterm (34 - 36), early term (37–38) and term (≥39) weeks gestation. Design: A single site prospective observational study. Setting: A postnatal ward and special care baby unit in a major tertiary hospital in Australia. Participants: Newborns from 34 weeks gestation admitted to either the postnatal ward or special care baby unit. Methods: Heart rate, respiratory rate and oxygen saturation were continuously monitored for up to 6 h. Newborn temperature and blood pressure were measured twice during the monitoring period. Results: Continuous monitoring resulted in 284,542 heart rate, 275,826 respiratory rate, 287,572 SpO values, and 60 temperature and 60 blood pressure data points. Heart rate was significantly different between gestational age groups with late preterm heart rates 13.4 bpm (95% CI 6.5–20.4) higher than term newborns. Early term heart rates were 2.3 bpm (95% CI -4.6 – 9.3) higher than term newborns, although not statistically significantly different. Heart rate was significantly different based on sex with females on average 7.7 beats per minute (bpm) (95% CI 1.9–13.5) higher than males. Respiratory rate was not significantly different between gestational age groups however, on average, was −2.0 respiration rate per minute (rpm) (95% CI -6.8 – 2.7) lower for late preterm babies and −1.3 rpm (95% CI -6.0 – 3.4) lower for early term babies compared to term newborns. SpO was not significantly different between gestational age groups, however, on average was −1.17 log units (95% CI -2.32 to −0.01) lower for late preterm newborns and −1.00 log units (95% CI -2.16 – 0.15) lower for early term newborns compared to term newborns. Respiratory rate and SpO were neither clinically nor statistically significantly different by sex. There were no significant differences between gestational age groups for temperature (p = 0.38) or blood pressure (systolic p = 0.93, diastolic p = 0.54). No significant mean differences were observed based on sex for temperature (p = 0.57) or blood pressure (systolic p = 0.98, diastolic p = 0.40). Conclusions: This study demonstrated a clinically significant higher heart rate in those born late preterm. This may have implications for current “one-size fits all” newborn early warning tools, as well as care of well late preterm infants in maternity units