Today show presenter Sarah Abo has left the breakfast program ahead of schedule to begin maternity leave, after experiencing a series of health scares that have left her in and out of hospital in recent days.

Co-hosts Sylvia Jeffreys and Charles Croucher broke the news to viewers on Wednesday morning, passing on a message directly from Abo, who had been hoping to return to the studio to farwell her audience in person before heading off.

High blood pressure forces Sarah Abo off the Today show sooner than planned

Jeffreys told viewers that Abo had experienced a "curveball" the previous week, revealing the presenter had been dealing with high blood pressure and had been hospitalised as a result.

"She wanted us to share that while her little man isn't here just yet, last week she received a bit of a curveball with high blood pressure, and she's been in and out of hospital," Jeffreys said on air.

Croucher added that Abo is currently being cared for by her medical team, and that doctors have instructed her to rest — ruling out any chance of a farewell appearance in the studio.

"They've asked her to rest. Sarah was hoping to return to the studio to say goodbye to you all and head off on maternity leave. We were looking forward to saying goodbye to her, but doctor's orders mean that that's not possible right now," Croucher said.

Abo, who had been a prominent face on the weekday breakfast show, was photographed at her baby shower in Carlton, Melbourne, in recent weeks ahead of the arrival of her son.

Abo's departure adds to significant upheaval on the Today show

The news comes at a turbulent time for the program, following the high-profile exit of co-host Karl Stefanovic. It is understood Nine terminated Stefanovic's multimillion-dollar contract after he interviewed British far-right figure Tommy Robinson on his podcast in June.

Nine chief executive Matt Stanton addressed staff on the matter, saying it was "the right time for Karl to move on from the Today show and Nine." Stanton acknowledged the significance of the change, noting Stefanovic had been "a fixture on our screens for over two decades."

With both Abo and Stefanovic now off the desk, the breakfast show is navigating a period of considerable change in its presenting lineup. Nine's Melbourne newsreader Tom Steinfort and Croucher have been filling in for Stefanovic in recent weeks, while no permanent replacement has been announced.

What happens next for the Today show lineup?

Nine has not yet confirmed who will permanently step into Stefanovic's role. It is understood the network has been making internal plans since Stefanovic notified management some months ago of his intention to leave. Historically, Nine tends to promote from within its own stable of talent, making it unlikely an external figure would be brought in to take the seat.

In the meantime, viewers can expect the current fill-in arrangement to continue while the network works through its options — and while Abo focuses on her health and the imminent arrival of her baby.

The Today show's audience has been left to wish Abo well from a distance, with her on-air family of colleagues conveying her warmest regards in lieu of a personal goodbye.