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Your Baby's Temperature and Fever

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

Reviewed by Dan Brennan, MD on May 27, 2015

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