Axillary and rectal thermometry in the newborn: do they agree?

Accurate measurement of body temperature is critical for the assessment of a newborn's general well-being. In nursery settings, the gold standard rectal thermometry has been replaced by the axillary method. However, evidence pertaining to the agreement between axillary and rectal thermometry in the newborn is controversial. In this cross-sectional study, the agreement between axillary and rectal temperature in newborns, as well as the effects of neonatal, maternal and environmental factors on this agreement were investigated.

The mean difference between axillary and rectal temperatures was compared in stable term and preterm newborns using paired t-test for the means of differences, Pearson correlation coefficient (r), and the Bland-Altman plot. Stepwise multivariate regression assessed predictors of this difference in the overall group and by gestational age categories.

The study included 118 newborns with gestational ages ranging from 29 to 41 weeks, median birth weight of 2980 grams (IQR: 2321.3-3363.8). Axillary and rectal temperatures correlated significantly (r = 0.5, p = 0.000) and had similar overall means but differed in 34-36 weeks gestation newborns (p = 0.01). Correlation between both methods increased with advancing gestational age being highest in term newborns (r = 0.6, p = 0.000). Bland-Altman plots revealed good agreement in gestational ages above 29 weeks. The difference between measurements increased with Cesarean delivery (ß = 0.2; 95% CI: 0.02, 0.38), but decreased with advancing chronological age (ß = -0.01; 95% CI: -0.02,-0.01), and with gestational age (ß = -0.05; 95% CI: -0.08,-0.01).

In clinically stable term and preterm infants, axillary thermometry is as reliable as rectal measurement. Predictors of agreement between the two methods include gestational age, chronological age and mode of delivery. Further studies are needed to confirm this agreement in sick newborns and in extremely premature infants.