A good cry lets baby test out their lungs for the very first time. In actual fact, babies “practice” the motion of crying before birth, as if they instinctively know that this will cause their lungs to expand.
Before your little one is born, it takes in oxygen through the placenta via the umbilical cord, but the moment the baby leaves the womb, it’s on its own, so to speak. Natural instinct kicks in; we must breathe or we will die. So your baby does the only thing it can; it gives a good scream. The lungs will fill up with air and for the very first time expand to their full capacity.