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If you hear gulping noises, the baby may be eating too quickly and swallowing air. Swallowing excess air can cause an infant's stomach to distend, leading to hiccups. Take frequent breaks to slow the feeding session. The infant's lips should cover the areola, not just the nipple. An insecure latch can cause the baby to swallow air. This allows air in the bottle to rise to the bottom and away from the nipple. You may also want to consider using collapsible bag inserts for the bottle that are designed to reduce air swallowing. If the hole is too big, the formula will flow too quickly, and if it is too small your baby will grow frustrated and gulp air. If the hole is the proper size, a few drops should come out when you tip the bottle.
Listen to the infant during feedings. Check that the baby is latched on correctly if you are breastfeeding. Tilt the bottle to 45 degrees when bottle-feeding. Check the hole in the bottle's nipple when bottle-feeding.