A newborn baby’s health is a frequent source of worry for parents. Infants younger than three months have developing immune systems and cannot fight off infections as effectively as older children. For this reason, a fever in this age group is treated with greater seriousness. Understanding how to accurately recognize a fever and what steps to take next is a fundamental part of newborn care.
Defining a Newborn Fever
A fever in an infant aged 0 to 90 days is defined by a specific temperature threshold accepted by healthcare providers. This threshold is a rectal temperature of 100.4°F (38°C) or higher. This exact number is the established marker for concern in a newborn, regardless of how well the baby may appear. This measurement is considered the most reliable indicator of a true elevation in core body temperature for this age group.
This temperature is treated as an urgent medical event due to the potential for a serious underlying infection. The initial signs of severe bacterial illness, such as sepsis or meningitis, can be subtle in a young infant. A fever may be the only initial symptom, and infections can progress rapidly. Any reading at or above 100.4°F requires immediate attention from a medical professional.
Measuring Temperature Accurately
The most precise method for measuring a newborn’s temperature is using a digital multi-use thermometer rectally. Accuracy is paramount in infants under three months, which is why other methods are not sufficient for a definitive diagnosis. Devices that measure temperature via the ear canal are not reliable until a baby is at least six months old. Readings taken from the armpit are the least accurate and should only be used as a preliminary screening tool.
To perform a rectal temperature check, use a clean digital thermometer and petroleum jelly for lubrication. Place the baby on their back with their legs pulled up toward their chest, or on their stomach across your lap. Gently insert the lubricated tip into the rectum, no more than one-half to one inch, or until the silver tip is no longer visible. Hold the thermometer in place until the device beeps, which typically takes around ten seconds. After the reading, clean the thermometer thoroughly with cool water and soap or rubbing alcohol.
Recognizing Other Signs of Illness
While a temperature reading is definitive, a newborn may show other signs of illness even before a fever registers. Behavioral changes are often the first observable indicators. An infant who is unusually sleepy or lethargic and difficult to wake for feedings may be ill, as reduced energy is a common symptom.
Feeding habits provide another clue, such as refusing multiple feedings or having a weak suck. Respiratory distress can manifest as rapid breathing, a throaty noise, or a pulling in of the skin between the ribs with each breath. Changes in skin color, such as paleness, blotchiness, or a grayish hue, can signal a serious issue. A sharp decrease in wet diapers, defined as no urination in eight hours, suggests dehydration and requires immediate attention.
Urgent Action Steps
If a rectal temperature measurement in a newborn under three months reaches 100.4°F (38°C) or higher, contact your pediatrician immediately. This is not an instance for observation or home remedies, as the risk of a serious infection is too high. Have the temperature reading, the time it was taken, and the method used ready to share with the provider.
Healthcare professionals often advise against giving any fever-reducing medication without their explicit instruction. A doctor may instruct you to proceed directly to the emergency room, particularly if the baby is younger than two months old. Immediate medical attention is necessary if the infant displays severe symptoms, such as being unresponsive, having difficulty breathing, or exhibiting a seizure.