Fever in newborns (0-4 weeks old)

What causes a fever?

Fever is an abnormal elevation of body temperature that results from signals sent by the immune system and affect the temperature centers of the brain. These signals are an indication of inflammation that can be a marker of infection (viral, bacterial, parasitic or fungal). In the very young, this can be the only sign of a serious infection, for this reason, when a newborn has a fever, they need to be evaluated by a medical professional

What temperature defines a fever?

Fever is defined as a measured body temperature of 100.4F (38C) or higher. The most accurate method for measuring a temperature in infants is rectally, followed by the forehead (temporal). Oral measurements are difficult in this age group and those in the armpit/ear are not as accurate.

Instructions on how to measure a rectal temperature can be found on this AAP website

What happens if my newborn (0-4 weeks) has a fever ?

Due to age and a relatively immature immune system, newborns have a significant risk for developing serious/invasive bacterial infections (i.e bacteremia, meningitis, UTI). The source of these infections can stem from events while in the womb, during delivery or thereafter. The risk for a serious bacterial infection increases in those whom are premature (born less than 37 weeks old), had medical complications during/after delivery and/or exposed to maternal infection. For this reason, anytime a newborn has a fever, they require a visit to an emergency room where thorough evaluation can be undertaken. Based on AAP guidelines, infants less than four weeks should have blood work, urine tests and lumbar puncture (based on age and other risks) completed. It is also recommended that they are treated with empiric antibiotics+/-antivirals and observed in the hospital while awaiting results, especially within the first 3 weeks of life.