Objective: This study aimed to evaluate the developmental occurrence of inspiratory phonations (IPs) in the spontaneous cries of healthy infants across the first 10 weeks of life.
Study design: This is a populational retrospective study.
Participants: The spontaneous crying of 17 healthy infants (10 were male) was retrospectively investigated.
Materials and methods: Sound files of spontaneously uttered cries that were repeatedly recorded once per week for across the first 10 weeks of life were retrospectively analyzed. Frequency spectra and waveforms were used to identify the occurrence of IPs and to measure the duration and fundamental frequency (fo) of each instance of IP.
Results: A consistent number of IPs were identified across the 10-week period. All infants were observed to produce IPs in their spontaneous cries, although the frequency of occurrence was not consistent across infants. A marked sex difference was observed with female infants producing a higher number of IPs compared to males. The duration and fo of IPs did not differ significantly across the 10 weeks or between sexes.
Conclusions: The production of IPs is a regularly occurring phenomenon in healthy, normally developing infants' spontaneous crying. The proportional difference in the production of IPs between female and male infants, observed for the first time here, is postulated to be linked to sex-based differences (including steroidal hormones) in respiratory anatomy and physiology.
Keywords: Cry; Fundamental frequency; Infant; Inspiratory phonation; Sex difference.
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