Spontaneous activities of female versus male newborns.
This study explored potential sex differences in all activity spontaneously emitted by newborns. 2 groups of full-term infants (14 uncircumcised males, 15 females), equally distributed along several physical and demographic variables, served as subjects. Each newborn was observed for a total of 8 hours during the 2 days following birth. Observational procedures were stringently controlled and interobserver reliability ranged from .84 to .98. Results showed higher levels of wakefulness, facial grimacing, and low-intensity motor activity for males. Of marginal significance, both low-intensity and high-intensity oral activity was higher for males. In addition, a marginally significant interaction effect (sex X interfeeding interval X day) was found for high-intensity oral activity (crying). Independent of sex, high-intensity activity increased in the evening and over an interfeeding period, and low-intensity oral activity increased over days. The pattern of results indicates that even uncircumcised males may be slightly more irritable than females, and thus more active. Potential implications of these findings are considered.
D002940:Circadian Rhythm; D003448:Crying; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009043:Motor Activity; D012737:Sex Factors