Bush, now age 92, has decided not to seek additional medical treatment and will instead focus on comfort care. She has six children, including former President George W. Bush.
The short statement did not indicate the nature of Mrs Bush's illness but said that she had had a series of recent hospitalisations.
Former first lady Barbara Bush attends the UNICEF Audrey Hepburn Society Ball honoring her on November 6, 2015, in Houston. Jim McGrath, who issued a statement, said that she is surrounded by a familyand appreciates the messages and prayers she's been receiving from people. The other was Abigail Adams, wife of John Adams and mother of John Quincy Adams.
She is also grandmother to George P. Bush, the current land commissioner of Texas. Her husband was president from 1989 to 1993. He is 93 years old and also has been in failing health in recent years.More news: Donald Trump is losing it on Twitter over James Comey
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The former first lady has reportedly been battling chronic obstructive pulmonary disease and congestive heart failure.
"Barbara and I are so sorry we can't be there for your Inauguration on January 20th", Bush wrote at the time. He also served as a congressman, Central Intelligence Agency director and Ronald Reagan's vice president.
The couple met at a Christmas dance in 1941, when Barbara Pierce was 16 and George Bush was 17. Her father was the publisher of McCall's and Redbook magazines. After leaving the White House, Barbara Bush and her husband retired to Houston. After World War II, the Bushes moved to Texas where he went into the oil business.