Monitoring a newborn’s well-being requires recognizing changes in body temperature. A fever in an infant under three months old is not a simple symptom to manage at home and requires immediate medical attention. Because a very young infant has an immature immune system, what might be a mild infection in an older child can quickly become a serious health issue. This article provides guidance on identifying, accurately measuring, and responding to a fever in your newborn.
Defining a Newborn Fever
A fever in a newborn is defined by a specific temperature threshold. For an infant less than three months old, the standard medical definition is a temperature of 100.4°F (38°C) or higher, typically confirmed with a rectal measurement. This relatively low temperature is considered a medical emergency because the newborn’s body has limited ability to fight off a serious bacterial infection.
Since the developing immune system cannot effectively contain an infection, bacteria can spread rapidly into the bloodstream, potentially causing sepsis. Therefore, a fever in this age group is treated with caution as a sign of a serious underlying illness, such as a urinary tract infection, pneumonia, or meningitis.
Accurate Temperature Measurement Techniques
Obtaining an accurate temperature reading is paramount, and for infants under three months, the rectal method is considered the most reliable gauge of core body temperature. Use a digital thermometer, which is safer and more accurate than older glass mercury thermometers. To prepare for a rectal reading, lubricate the tip with a small amount of petroleum jelly.
The baby should be positioned either on their back with their legs held up, or on their belly across your lap. Gently insert the lubricated tip into the rectum about one-half to one inch, or until the silver tip is no longer visible. Hold the thermometer securely until the measurement is complete, and never leave the baby unattended during this process.
While other methods like axillary (armpit) or temporal (forehead) readings can be used for an initial check, if any suspicion of a fever exists, the measurement must be confirmed with the more precise rectal method.
Recognizable Physical Symptoms
Changes in a newborn’s behavior or appearance can signal a possible illness before a temperature is taken. Parents might observe a significant change in alertness, such as unusual lethargy or difficulty waking the infant. Conversely, the baby might display increased irritability, crying inconsolably or sounding different than typical fussiness.
Physical cues include skin that is flushed, warm to the touch, or clammy and sweaty. Other warning signs are changes in feeding habits, such as poor feeding or refusal to take the breast or bottle. Parents should also watch for changes in diaper output, as fewer wet diapers can indicate dehydration.
Immediate Steps After Confirmation
When a rectal temperature confirms a reading of 100.4°F (38°C) or higher in a newborn under three months old, immediately seek medical attention. Contact your pediatrician or proceed to the nearest emergency department right away. A medical evaluation, often including diagnostic tests, is necessary to rule out a serious bacterial infection due to the severity of fever in this age group.
Before administering any medication, consult with a healthcare professional. Fever-reducing medicines are discouraged for infants under three months until a full medical evaluation is performed, as they can mask the fever and delay diagnosis. Be prepared to state the baby’s exact temperature, the time it was taken, the method used, and any other symptoms observed. Never give aspirin to an infant or child, as it is linked to Reye syndrome.