Development of night time temperature rhythms over the first six months of life.

Continuous recordings of night time rectal temperature were made at regular intervals over the first six months of life in 49 babies. In the first two weeks of life rectal temperature changed little overnight, but by 6 weeks of age rectal temperature at bedtime was significantly higher than later in the night. By around 12 weeks of age sleeping deep body temperature fell below 36.5 degrees C, and by 16 weeks of age all babies exhibited a consistent rhythm of rectal temperature. This fell by about 0.8 degrees C within two hours of bedtime, and then remained low until an hour or two before waking. As babies got older the mean interval between bedtime and first disturbance of parents got longer. Sleeping rectal temperature fell below 36.5 degrees C at about the time babies slept for seven hours. From 6 weeks of age, as individual baby's rectal temperatures fell more with sleep, sleep got longer.