In a sharp change to his campaign tactics, Mr Romney, who has tried to rise above squabbles with rivals, began alluding to Mr Gingrich's personal life to try to reverse his surge in the opinion polls.
In a television advert to be broadcast in Iowa, the socially-conservative state first to vote in the contest, Mr Romney said he had been married to his wife Ann for "42 years", to a slide show of family pictures.
"If I'm President of the United States, I will be true to my family, my faith and our country," he said.
In a speech in Washington, Mr Romney described his "42-year marriage" as one of the "defining constants in my life". He added: "My commitments are firm, and they do not falter."
Mr Gingrich divorced his first wife, Jackie, in 1980 as she was in hospital recovering from surgery to remove a tumour. She had previously suffered from cancer.
After marrying his second wife, Marianne, he had an affair with Calista Bisek, a staff member 23 years his junior, even while leading an inquiry into President Bill Clinton's liaisons with Monica Lewinsky.
He eventually married Miss Bisek in 2000 following a divorce from Marianne, who had been diagnosed with multiple sclerosis eight months earlier. Read on and comment » | Jon Swaine, Washington | Wednesday, December 07, 2011
