Results:
Three hundred fifty-one infants completed the study. Prone sleepers acquired motor milestones at an earlier age than supine sleepers. There was a significant difference in the age of attainment of rolling prone to supine, tripod sitting, creeping, crawling, and pulling to stand. There was no significant difference in age when infants walked.
Conclusions:
The pattern of early motor development is affected by sleep position. Prone sleepers attain several motor milestones earlier than supine sleepers. However, all infants achieved all milestones within the accepted normal age range. Pediatricians can use this information to reassure parents. This difference in milestone attainment is not a reason to abandon the American Academy of Pediatrics' sleep position recommendations.