Position your baby on his/her back on a changing table. Spread apart your baby’s buttocks with one hand. Use the other hand to grasp the thermometer between you middle and index finger. Gently insert the bulb of the thermometer about 1 inch (2.5cm) into the rectum or until the tip of the thermometer disappears. Keep a firm grasp on the buttocks by cupping them with the palm and fingers of the hand that is holding the thermometer.