You may notice that your baby sometimes stops breathing for a few seconds while sleeping. It's normal for newborns to have "periodic breathing." They usually have a period of rapid breathing followed by a period of slow breathing, then a brief pause of up to ten seconds. The cycle then repeats. Breathing pauses happen because the part of your baby's brain that controls breathing is still developing, says Lewis Kass, M.D., a pediatric pulmonologist at Westchester Pediatric Pulmonology and Sleep Medicine, in Mount Kisco, New York. Unlike sleep apnea, periodic breathing doesn't cause snoring or struggles for breath. As long as your baby seems comfortable, isn't gasping for air, and her fingernails and lips don't change color, don't worry. Usually, by 4 to 6 months, the sleep-time breathing pattern becomes more regular.