Baby hiccups are caused by a contraction of the diaphragm followed by the quick closing of the vocal cords. The sound of the vocal cords closing is what creates the familiar “hiccup” noise.
Since hiccups tend to bother adults, families assume they will in turn bother their baby as well.
The good news, babies are typically not affected by hiccups at all. In fact, many babies will even sleep through the hiccups without being disturbed.