The visitors took a two-goal lead at Ewood Park through Njazi Kuqi and Neil Kilkenny but a Jemal Johnson brace, the second from the penalty spot, levelled the scores.
Birmingham defender Marcos Painter put Birmingham 3-2 ahead but a late equaliser from Jonathon Douglas earned Rovers a share of the spoils and kept them at the top of the Reserves league table.
Rovers: Enckelman, Barr, Gray, Douglas, Harkins, Nolan, Sakali, Flitcroft, Johnson, Garner, Byrom. Subs: Treacy, Drench, Stopforth, Rowntree, Welch.
Birmingham: Doyle, Cottrill, Alsop, Painter, Davies, Howland, Wright, Kilkenny, Till, Kuqi, Birley. Subs: Legzdins, Blake, Oji, Howell, Mark Hall.