Sex differences in the ontogeny of sleep apnea during the first year of life

Respiration and behavioral sleep states were studied in full term, normal infants under natural circumstances over the first year of life. Sixteen male and 12 female infants were observed during an interfeeding period in the hospital at 2 days of age; in the home during a 7-hr period whenever the infants were put down to nap on weeks 2, 3, 4, and 5; and in the home during the first 2 hr of overnight sleep at 3, 6, and 12 months of age. From analog recordings of respiration, all apneic episodes, or respiratory pauses, of 2 sec or longer were measured. Analyses of these data were made for active and quiet sleep states separately. During active sleep, female infants had higher frequencies of apneic episodes and greater total duration of apnea during observations at all ages through 6 months of age; during quiet sleep females had greater frequency and duration of apnea through 3 months of age. The two sexes did not differ with respect to the mean length of apneic episodes in either sleep state. However, females had longer single apneic episodes in both sleep states throughout the first year. The two sexes also differed in their predictability of apnea levels. Female infants were predictable at all ages from one observation to another throughout the first year of life. For the male infants, there were significant correlations within the first 5 weeks and between 6 months and 12 months; however, the correlations from between the first 5 weeks and 6 months were not significant. The results of this study of infants during naturally occurring sleep periods indicate a differential ontogeny of apnea in normal male and female infants. Females had higher levels of apnea and more predictable apnea characteristics than males through 6 months of age. These early sex differences in respiratory function may have implications for the occurrence of SIDS, which has the highest incidence during the first 6 months of life.