Call a pediatrician if your newborn's rectal temperature hits 100.4 F (or 101 F if your baby is 3 months or older).
Fever can be a sign of serious illness, especially in a newborn. Call a pediatrician if your newborn's rectal temperature hits 100.4 F (or 101 F if your baby is 3 months or older). Also, watch for other signs of illness: If your baby is acting oddly, not eating or drinking, or seems to be in pain, contact a health care provider regardless of their temperature.