Because an inch or a pound can make a pretty significant difference in where your baby falls on the charts, your child is measured very carefully. It can be tricky to get reliable and accurate numbers – especially if your baby is very squirmy! – but most doctors and nurses are experienced at it.
The doctor or nurse takes three measurements:
After you undress your baby completely – that's right, no diaper – the doctor or nurse places her on a scale (either a traditional beam scale or an electronic model). Weight is measured in pounds to the closest ounce or in kilograms to the nearest tenth of a kilo.
While your child is lying down, the doctor or nurse measures her from the top of her head to the bottom of her heel. Some doctors use a special device with a headboard and a movable footboard for more accurate results.
To measure your baby's head, the doctor or nurse places a flexible measuring tape where your baby's head has the largest circumference – just above the eyebrows and ears, and around the back of the head where it slopes up prominently from the neck.
Why does the size of your baby's head matter? Because the size of her skull reflects the growth of her brain.
So if a baby's brain isn't growing and developing normally, her head circumference may not be increasing as it should. On the other hand, if the skull grows too quickly, it could be a sign of a problem like hydrocephalus (the buildup of fluid in the brain). Both conditions are unlikely, but important to rule out.
By the way, babies' heads are disproportionately large compared to adults' heads, so don't worry if your baby's head looks big to you. Consider your own proportions, too: If you or your partner has a large or small head, your baby might, too.