The purpose of this study was to assess differences in sound spectra of crying of term newborns in relation to different pain levels. Fifty-seven consecutively born neonates were evaluated during heel-prick performed with different analgesic techniques. Crying was recorded and frequency spectrograms analyzed. A pain score on the DAN (Douleur Aigue do Nouveau-ne) scale was assigned to each baby after the sampling. Three features were considered and correlated with the corresponding DAN scores: 1) whole spectral form; 2) the fundamental frequency of the first cry emitted (F-0); and 3) root mean square sound pressure normalized to its maximum. After emission of the first cry, babies with DAN scores >8, but not with DAN scores less than or equal to8 (p < 0.001), showed a pattern ("siren cry") characterized by a sequence of almost identical cries with a period on the order of 1 s. A statistically significant correlation was found between root mean square (r(2) = 89%, p < 0.01), F-0 (r(2) = 32%, p < 0.05), siren cry (r(2) = 68.2%, p = 0.02), and DAN score. F-0 did not show significant correlation with DAN score in the subset of neonates with DAN scores less than or equal to8 (r(2) = 1.4%, p = 0.94), and babies with a DAN score >8 had a significantly higher F-0 than those with lower DAN scores (p = 0.016). An alarm threshold exists between high (>8) and low (less than or equal to 8) DAN scores: crying has different features in these two groups. When pain exceeds a DAN score of 8, usually a first cry at a high pitch is emitted, followed by the siren cry, with a sound level maintained near its maximum.
