The Girls Aloud star admitted that all the girls thought Kimberley would be the first band member to fall pregnant, but that Nadine - who had her daughter earlier this month - beat her to it.
Speaking on ITV1's Lorraine today, Sarah joked: "I think we all expected Kimberely to be the first one!"
She added: "I [then] kind of thought, if it would be anyone, it would be Kimberley next, but I didn't expect it so soon!"
Since Girls Aloud split last year, Sarah has settled down in the countryside with her boyfriend Mark Foster and their pet dogs and cats.
But are babies on the cards?
"Apparently I'm next in line....not yet, not yet!" she laughed. "Maybe one day but I've still got a few more boxes to tick."
Host Lorraine Kelly remarked that she would be an honorary auntie to Nadine's daughter and Kimberley's unborn child.
Sarah replied: "And I've got three godchildren and my animals. That's enough for now!"
Stars congratulate Kimberley Walsh on her pregnancy: