While most people recover without medical intervention, the risk of severe complications, including hospitalisation and death, is highest in very young babies.
Er bod y rhan fwyaf o bobl yn gwella heb ymyrraeth feddygol, mae'r risg y bydd cymhlethdodau difrifol, gan gynnwys mynd i'r ysbyty a marwolaeth, ar ei huchaf ymhlith babanod ifanc iawn.