The Lions came away from the Easter weekend with another four points under their belts after a draw on the road against Preston North End before returning to The Den and defeating Hull City.
They now face another trip away but they face a Blues side who are woefully out of form and who lost their last match 6-1 against Blackpool, so Gary Rowett may fancy his chances massively against a former club.
Millwall quiz: Does The Den have a bigger or smaller capacity than these 20 stadiums?
He will have some dilemmas going into the contest though – let’s look at two that he could be weighing up.
Who replaces Malone?
Almost an ever-present in the Millwall side this season having missed just four league matches, Scott Malone will be absent for the trip to St. Andrew’s due to an injury.
Malone scored his first goal of the season on Monday against Hull in somewhat fortuitous circumstances, but then he had to hobble off not long later.
It means that Rowett needs to select who replaces him, with the obvious choice being Murray Wallace shifting over to the left wing back role and bringing Shaun Hutchinson back into the fold in the back three.
There’s no-one else to really play that role for Rowett, but he could spring a major curveball and change the formation, which would mean Wallace playing as a left-back in a back four and an attack-minded player comes in for Malone instead.
Kieftenbeld or Saville?
After starting the previous two matches, Maikel Kieftenbeld dropped out of the starting 11 against Hull to be replaced by George Saville, and that ended up being a change that contributed to a winning result.
Kieftenbeld though is an ex-Birmingham player so he would be very much up for this particular fixture should he come back in for Saville – but there’s always the chance that they could feature in the same team.
If Rowett wanted a more solid midfield then perhaps Tyler Burey could drop out of the attacking midfield role and Saville could push further forward in Jed Wallace’s absence, but with how fragile Birmingham have been in defence lately it’s perhaps not the right match to withdraw an attacking presence like Burey for a central midfielder.