From the
Contract of Carriage :
5) Baggage will not be checked:
e) To an intermediate point unless the intermediate point to which the Baggage is to be checked is a permissible Stopover point at the fare paid (except if the Passenger is making a connection to the first available UA flight departing from such intermediate point and the connection exceeds four hours, the Passenger may reclaim his/her Baggage at such intermediate connecting point).