Rectal or axillary temperature measurement: effect on plasma bilirubin and intestinal transit of meconium.

Physiologic jaundice (5-6 mg/100 ml plasma bilirubin) is common and considered normal in newborn infants during the first week postbirth, but is considered abnormal in older infants. Early meconium passage correlates with lower plasma bilirubin concentrations. Rectal stimulation during rectal temperature measurement may aid passage of meconium containing potentially toxic, absorbable bilirubin. In this study, 100 clinically normal infants were assigned randomly to groups for rectal or axillary temperature measurement. The time of first meconium passage, time of first all-yellow stool, and total plasma bilirubin were compared between groups. Bilirubin was measured during metabolic screening at 48-80 h postbirth (mean 69 h in both groups). By this time 30 infants in the rectal group, but only 17 in the axillary group, had passed yellow stools (p = 0.011). The rectal group had lower mean (+/- 1 SD) bilirubin (5.5 mg/100 ml +/- 2.7 vs. 6.5 +/- 3.0, p = 0.042), and a trend toward earlier first meconium (5.9 h +/- 5.0 vs. 7.3 +/- 5.9, p = 0.096). For clinically normal infants in the first 48-80 h postbirth, these data suggest that rectal stimulation accompanying rectal temperature measurement enhances intestinal bilirubin excretion because of more rapid meconium passage.