Why does baby hiccup in sleep?

Baby hiccupping in sleep is quite common and usually normal. There are a few reasons for this:

Your baby's breathing centers haven't fully matured yet. Hiccupping is actually a kind of "breathing reset" — it reopens tiny air sacs in the lungs (alveoli) and regulates the oxygen-carbon dioxide balance. This mechanism exists in adults too, but shows up more frequently in babies because their breathing is more irregular.

Especially in the newborn period (0-3 months), babies breathe in sleep following what's called periodic breathing: fast for a while, then slow, sometimes with 5-10 second pauses, then a deep hiccup. This is a normal part of development.

When should you worry? If your baby has bluish discoloration during or between hiccups, has trouble breathing (flaring nostrils, ribs pulling inward), or is persistently fussy and you hear labored breathing even when awake, consult your pediatrician. Hiccupping alone is just something all healthy babies in the world do—it's ordinary.