The objective of this study was to determine the influence of fetal growth on the fundamental frequency (F(0)) of neonatal crying in a group of healthy full-term infants. The spontaneous cries of 131 infants were audio recorded during the first week of life, and subsequently submitted to acoustic analyses. The individual cry utterances produced by each infant were measured for minimum, mean, and maximum F(0). The infants were placed into one of three groupings (low, average, high) based on body size indices according to the ponderal index (PI), the ratio of body weight to body length (BW/L), and body weight (BW) alone. The F(0) features of infants in each subgrouping of body size were compared and contrasted. The results indicated that features of cry F(0) were found to decrease marginally as a function of increased body size, with significant group differences confined to maximum F(0). The BW index appeared to be the most sensitive measure in differentiating infant groups according to body size. In general, neonatal body size appears to have a slight, although nonsignificant influence on the vocal F(0) of crying in healthy full-term infants. Any body size-related changes in cry F(0) are likely to be found for maximum F(0) and may reflect stress-related variations in nervous system activation.
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