Newborn infants' cry after heel-prick: analysis with sound spectrogram

The aim of the study was to test the hypothesis that a newborn infant's cry can be used in conjunction with an instrument to measure pain. Crying due to pain was analysed after a heel-prick stimulus. In a prospective, descrip tive study, 50 healthy newborn infants were subjected to a heel-prick for p henylketonuria screening. Their cries of pain were recorded and analysed. D uration of the crying sound was analysed and, using a sound spectrogram, th e fundamental frequency and the cry melody of the first five cry sounds wer e analysed. The analysis showed that the crying sound after the painful sti mulus of the heel-prick had a significantly higher fundamental frequency an d lasted longer at the first than at the fifth cry. The first cry had a mor e varied crying melody than the fifth. There were large differences between individual cries from a single infant, as well as in the duration of each cry, total crying time, and fundamental frequencies between infants. While the first cry was more like a cry of pain, the fifth cry more resembled cry ing for reasons other than pain. The results suggest that newborn infants r eact to pain in a recognizable way. However, other stimuli may cause a simi lar reaction. Crying can therefore be used to measure pain in newborn infan ts only when the cause of crying is known.