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    During the first few months of your baby’s life, pay special attention if you think she has a fever. Her immune system isn’t as good at fighting infections as it will be at 3 or 4 months of age.

    When Is It a Fever?

    Most doctors say a baby has a fever if her temperature rises to 100.4 F or above. It’s best to take her temperature rectally. Take a few readings when your infant is well to get a sense of what her normal temperature is.

    When to See a Doctor

    If your baby is under age 3 months and has a fever, take her to a doctor. For at least the first 6 months of life, call your doctor anytime she has a fever.

    At your baby’s next checkup you can ask if the doctor has a “fever policy.” That will give you a better idea about when you need to call. If you’re worried, take the better-safe-than-sorry approach: Dial him up.

    Fever is only part of the story. Sometimes a baby can be sick even if she doesn’t have a fever. A more important question is: Does your newborn show other symptoms of illness? Call the doctor if your baby:

    • Is irritable
    • Is inactive
    • Is sluggish
    • Doesn't eat
    • Has trouble breathing
    • Has a rash
    • Vomits
    • Has diarrhea

    What Causes Fever?

    Your baby could have a fever for many reasons, but the most likely is infection. Simple things such as colds can cause a fever, but so can very serious infections such as meningitis. If your baby is under 3 months and has a fever, see a doctor.

    WebMD Medical Reference