The visitors fell behind to Clayton Donaldson’s 43rd-minute penalty before Michael Morrison added a crucial second – a goal McCarthy labelled a “disgrace” – shortly after the break.
Ipswich did pull a goal back with 20 minutes to go, through Adam Webster, and McCarthy felt his side were denied an legitimate equaliser by the officials to further sour his mood after just three wins in 14 league games.
“Birmingham’s second goal was a disgrace,” he said.
“The penalty also came from a corner and I thought we had a perfectly legitimate goal late in the game.
“The referee gave a foul against Christophe Berra who appeared to back into Ryan Shotton who had not jumped.
“But this is typical of what has been happening this season. We didn’t play badly and deserved something from the match.
“We need a little luck from somewhere. We didn’t start the game in the second half when we gave away the second goal which made it an uphill battle.
“The substitutes made a real impact and I was pleased with the improving form of Tom Lawrence.
“As a team we have not played badly in recent weeks but we have given away some soft goals as we did against Birmingham.”
Birmingham’s win was soured by a leg injury to goalscorer Donaldson, who was taken from the pitch a minute after his penalty.
The striker is set to be sent for a scan on the injury and Birmingham will be hopeful of good news after a steadying win following heavy losses to Newcastle and Barnsley.
“We knew had to get a result,” first-team coach Mark Sale said.
“We played well in stages but Ipswich didn’t give us much time on the ball.
“After scoring the two goals we then conceded a goal and we were a little nervy in the last 15 minutes.”