Judge Duncan Harvey and a jury of seven women and five men had initially heard that Dunn, while being restrained by Mr Dunn, had kicked Ms Wycliffe several times in the stomach.
During a police interview recorded a few hours after the assault, Dunn admitted grabbing Ms Wycliffe and kicking her twice in the head, but denied ever kicking her in the stomach.
Dunn said that even though she did not believe that Ms Wycliffe was pregnant, she would still not have kicked her in the stomach "just in case".
Crown prosecutor Moana Jarman-Taylor had told the jury Dunn and her husband separated in October 2012 and Mr Dunn had been seeing Ms Wycliffe since July 2012.
Ms Jarman-Taylor said a month or so before the attack Ms Wycliffe told Dunn that she was pregnant to him, after she had found Mr Dunn at Terynne Dunn's home.
The prosecutor said about noon on May 11 Ms Wycliffe saw Mr Dunn's car parked at the Marist Rugby Club. She found Mr Dunn next to the playing field with his estranged wife and the two women got into a dispute. Ms Wycliffe was left with a bloody nose and scratches to her face. A subsequent hospital check found that there were no problems with her unborn child.
Ms Jarman-Taylor said three weeks before the attack, Dunn had contacted Ms Wycliffe on social media site Facebook, and verbally abused her.
Dunn said in the police interview that on May 11 she had told Ms Wycliffe several times to go away and could not understand why Ms Wycliffe was at her and Mr Dunn's son's rugby game.
"I just wanted her to go," she said.
Dunn said she and her husband were working towards a reconciliation when the assault occurred.
After she pleaded guilty to the lesser charge Judge Harvey told the jury they knew what the case had been about.
"This is a court of law, not a court of morals. But there are times when it's very difficult to see where one stops and the other starts," the judge said.
He said the police rightly charged Dunn and the Crown rightly took the case to court with the initial charges, but after hearing the evidence made the correct decision to amend the charge further.
Dunn will be sentenced on July 22.