The journalist and broadcaster shared her news with listeners on air this afternoon.
South Africa-born Du Plessis-Allan, who moved to New Zealand in her pre-teens, married political editor Barry Soper in 2009.
“I have something to tell you... don’t worry it’s not bad news,” she said. “The news is that I am pregnant.”
Although Du Plessis-Allan said it was scary, she and her husband were excited to meet “the wee mate”.
Du Plessis-Allan said she was due in February and expecting a boy.
While many listeners might be worried she will be off the airwaves for sometime, Du Plessis-Allan joked that her boss had kindly given her a week of maternity leave.