We recently took our infant on several flights.
On AC/UA flights, no problem gate-checking the stroller, and having
it returned to the gate ( on some flights in a very timely manner, on
others after everyone had deplaned!). TG - fast return at gate.
But beware: MF and CA gate checked the stroller, but only returned
it at the baggage pick-up area! Not good if you are doing in transit
connections!!!