I feed my 4-month-old, burp him, and he seems content, so I put him into the crib. He sucks his fist/thumb for a while, and then after about 30 minutes he gets fussy. As soon as I pick him up, he lets out a big burp, and he's content again.
That scenario happens pretty often, and I want to know: am I failing to burp him well enough after the feeding, or is he swallowing air while he sucks his thumb?
I have searched the pediatric literature using every combination of words I could think of, and could find nothing recent (this century) about this.
Most of the papers on belching were either associated with GERD (gastroesophageal reflux) or the willful swallowing of air (called Aerophagia) that is considered more of a psychological disorder in older children and adults.
So what follows is, unfortunately, opinion.
Can sucking thumbs lead to burping?
Not likely. But
Can sucking fist lead to burping?
Sure. A fist isn't really mouth saped and sucking on it probably means there is a bit of air sucked in (you'd hear a little slurpy sound), and infants especially (yours is a baby) do swallow when there is air in the pharynx that could be swallowed. So fist sucking could be responsible for the second belch.
However, if this were the case, it would happen every time the baby sucked on his hand, not only after feeding. If your baby sucks on his hand at other times as well as after feeding but doesn't experience discomfort then, it's probably due to the air ingested with food.
Interestingly, looking up how to properly burp your baby is not particularly helpful either. It doesn't mention how long after settling (or that first burp) that a baby might still need to be burped.
So the question of your proper burping of the baby is unsettled.
Practical advice: You're probably burping your baby just fine. He may or may not be sucking in air and swallowing it while fist sucking. But he needs to suck his fist to self soothe, so please let him do it. If he gets fussy every time, burp him. Eventually they get better about not swallowing air with sucking.
If it only happens with feeds, plan to re-burp the baby maybe 5 minutes after your initial burping (before he experiences discomfort) if the baby is not sleeping. Alternately, if you hold the baby upright after feeding, this might help cut down on the fussiness/burping.
You might want to mention this to your primary health provider during your next visit. This might be a sign of GERD, though spitting up is much more likely associated with GERD than excess belching.
I would say it's a combination. It's not to say you are not burping him well enough. Sometimes after feeding air gets stuck and only comes loose after he has laid down for a while. I found with my own two kids that trying too hard to burp them directly after feeding might also make them bring up the feeding.
In my own experience with my own children sucking on things didn't cause them to swallow air, but that might be different with other children and the way they suck. I don't think the swallow reflex kicks in unless there is actually something to swallow.
