How to take a baby’s temperature.

The AAP says:

• Rectal is the most reliable and accurate for infants, especially under 3 months.
• Oral, ear or forehead (temporal) readings can be used, with 100.4°F (38°C) still as the fever cutoff.
• Underarm readings may have a lower cutoff for a fever.
• Ear thermometers should be avoided under 6 months.
• Fever strips aren’t reliable.

Ask your doctor or nurse to show you the rectal method once, rather than learning it at 3 a.m.

The AAP gives these thresholds for when to contact your pediatrician:

• 3 months or younger: a rectal temperature of 100.4°F (38°C). Call right away.
• 3 to 6 months: 101°F (38.3°C) or higher.
• Over 6 months: 103°F (39.4°C) or higher.

These are triggers to call, not a diagnosis. How your baby looks and feeds matters as much as the number.

Don’t wait on a number if your baby seems very unwell. The NHS has a full list of when to get urgent medical help for babies and children under 5. The AAP says to call 911 if a febrile seizure doesn’t stop within 15 minutes or your child has trouble breathing.

Read the instructions that came with your thermometer, because each type works a little differently, and don’t take a reading right after a bath or while your baby is bundled up and crying hard. Wait a few minutes after a feed or a cuddle. Write down the reading, the time and the method used. The AAP’s cutoffs differ a little by method, so the doctor will want to know how it was taken.

The AAP says that if your child is especially miserable or has a fever above 100.3°F (38°C) that you think comes from teething, you should consult your pediatrician rather than assume. It also says that suspected heatstroke needs 911 or the emergency department right away. A very warm room or too many layers can raise a baby’s temperature, so check the room and the layers first, but don’t use that as a reason to delay a call for a baby 3 months or younger.

• Your baby’s age and last weight, if you know it
• The temperature, how you took it, and the time
• How they’re feeding and how many wet nappies they’ve had
• Other signs: rash, cough, vomiting, unusual sleepiness or fussiness
• Any medicine you’ve given, with the time

The AAP’s thresholds rise with age: 100.4°F (38°C) at 3 months or younger, 101°F (38.3°C) at 3 to 6 months, and 103°F (39.4°C) over 6 months. A young baby’s fever can be the only sign of a serious infection, which is why the AAP asks you to call right away for the youngest group. At any age, a baby who is hard to wake, struggling to breathe or won’t feed needs help whatever the number says.

A monitor can’t take a temperature. What it can do is let you see and hear your baby from another room, so you notice restlessness, fast waking or unusual crying earlier, and know when to go in with the thermometer. For the crying side, how to soothe a crying newborn covers when crying is a sign to call.

The nursery phone in a dark room shows what the phone’s camera can see; most phone cameras have no night vision, so a small night light may be needed.