ooner or later it will happen: Your baby is going to get a fever. But how do you know the difference between “hot and cranky” and a temperature due to illness?

It’s been nearly 300 years since German physicist Daniel Gabriel Fahrenheit invented the first mercury thermometer, and yet even in this digital age parents are somewhat confused about how to correctly take a baby’s temperature. Most pediatricians will tell you that the most accurate way to get a reading is with a rectal thermometer, but there are less “invasive” ways of getting the job done, too.

TYPES OF THERMOMETERS
The American Academy of Pediatrics (www.aap.org) discourages the use of glass mercury thermometers because of the possibility of mercury exposure. There are several safer alternatives:

• Digital Thermometers
  Safe, easy to use, and not too expensive, these readily available thermometers can be used for rectal, oral, or axillary (armpit) readings. Many baby books tell you not to use the same thermometer for rectal and oral, but most of us don’t need to be reminded of that.
  
  A digital thermometer gives a reading in about 20-60 seconds, and although this may seem like an eternity when you’re dealing with a squirming, feverish child, that’s fast in the world of thermometers. Digitals often come with a flexible plastic tip for added comfort.

• Pacifier Thermometers
  This is kind of like the baseball hat with built-in umbrella version of baby thermometers - a 2-in-1 contraption where neither function is handled particularly well. By combining a pacifier with an oral thermometer, you get a reading that takes three minutes to register and is usually between 0.2-0.5 degrees lower than core temperature. They are difficult to use with a fussing child and generally not recommended.

• Tympanic Thermometers
  These look like they came out of a first-aid kit on Battlestar Gallactica. Designed to take an instantaneous reading inside the ear canal by aiming infrared light at the eardrum, they deliver the news in seconds. Tympanics can be difficult to position, though - making them a poor choice for a child who won’t sit still - and they’re rather expensive ($25 - $50). Also, variations in earwax buildup can interfere with the reading. If used properly, these thermometers can work well for adults, but babies have very narrow ear canals and most pediatricians agree that tympanic thermometers should not be used with children under a year old.
• Temporal Artery Thermometers
  This type uses a transducer to get a reading off the forehead and is considered very accurate (though not as accurate as a rectal reading). They are expensive ($40-$50), but readily available at most medical supply stores. Some doctors caution, however, that fever-stressed babies may clamp down their skin’s blood supply, resulting in a falsely cool reading.

TAKING A READING
Before you get started, try to keep your baby calm and relaxed for 30 minutes or so. Crying and screaming can elevate body temperature and cause a falsely high reading. Avoid hot or cold drinks prior to an oral reading for similar reasons - though this precaution is not necessary when taking rectal, axillary, or tympanic readings.

An AXILLARY READING is preferable if your child has diarrhea or simply won’t sit still for a rectal reading (can you really blame him?). You can use a digital oral or rectal thermometer for an underarm reading. Be sure the underarm skin is dry and place the tip of the thermometer well up into the armpit, holding the arm snugly over it and pressing the elbow against your baby’s side. Distract your baby with carefully choreographed dance moves designed to hold a child’s attention for 60 seconds.

If your child is old enough to use a TYMPANIC THERMOMETER, try to get one with a feedback guide that helps you obtain the correct position - or ask your doctor for a demonstration. It’s a good idea to get comfortable with whatever method you’re going to use so that you’re prepared when that first fever comes.

According to The Cradle Advisory Board member JJ Levenstein, MD, FAAP, “The core, or true temperature of a baby is only reliable if taken rectally.”

Dr. Levenstein recommends the following method:

Lubricate the tip of your thermometer with a little petroleum jelly or KY jelly. Lay your baby on his/her tummy on a comfortable surface. Insert the thermometer 1-inch into the baby’s anus and pinch the buns together (this prevents baby from pooping on you). Use your other hand to put gentle pressure on baby’s lower back (decreases the wiggle factor). Wait a minute or two for your thermometer to beep, remove it and read it. If it registers 100.5 degrees or more, that is considered a fever.

Since different parts of the body will read different temperatures, “normal” depends on where you take the reading. In general, oral normal is 98.6 degrees, rectal is 99.6 degrees, and axillary is 97.6 degrees.

Children with fevers generally tend to be grumpy, fussy, and hard to console. Their sleep patterns become disrupted, they may show a decreased appetite, and appear listless or droopy. If you suspect a fever and find yourself without a thermometer, Dr. Levenstein says, “The best places to check for tactile temperature are a child’s belly or knees. The top of the head, especially in a young child, is the body’s radiator for losing excessive heat and energy on a regular basis and can’t be relied on to always predict a true fever.”

So get yourself a thermometer because sooner or later you’re going to need it. And although they lack a certain charm, rectal readings with a good digital thermometer are still considered the gold standard. Even if the process sounds daunting at first, with some guidance you can get past it in the name of parenthood and go for the gold.