In the book, due to be published on Tuesday, she also reflects on early struggles in her marriage to Barack Obama as he began his political career and was often away.
"He doesn't have a birth certificate, or if he does, there's something on that certificate that is very bad for him", Trump said during an interview with Fox News host Laura Ingraham in 2011.
It is one of the most awaited books about United States politics in years, and Obama does not mince words about her husband's successor - and his involvement in promoting the idea that Barack Obama was born overseas.
Someday I will write a book. "We had to do IVF".
In the book, which will be released on November 13, Obama reveals that she assumed Trump was "grandstanding" when he announced his presidential run in 2015.
Roberts' candid conversation with Obama about her journey to motherhood and more from her memoir, Becoming, will air during a prime-time ABC News special, Becoming Michelle: A First Lady's Journey with Robin Roberts, on Sunday, Nov. 11, at 9 p.m. ET.
"Donald Trump, with his loud and reckless innuendos, was putting my family's safety at risk", she added.
Yet she is also candid about the bleaker periods of her marriage, revealing for the first time that the couple sought counseling when their relationship was under stress. "But it was also unsafe, deliberately meant to stir up the wingnuts and kooks", Michelle wrote.
California wildfire leaves town in ruins, thousands flee
She captured photos of low-hanging black smoke stretching for miles as she and her boyfriend evacuated Paradise. Fire officials said some structures have been destroyed in addition to injuries.
She recalls her reaction when she heard Trump's Access Hollywood video where he brags about assaulting women, saying her "body buzzed with fury after hearing that tape".
"This was my pivot point", she writes.
Michelle Obama is not a fan of U.S. President Donald Trump.
Obama also reiterates that politics isn't for her, alluding to her previous dismissal of a potential 2020 presidential run.
She also can't believe so many women voted for a "misogynist" after all Trump has said. She writes about Mr Trump following Mrs Clinton around the stage, standing nearby and "trying to diminish her presence".
Widely praised as a gifted orator and communicator, Obama has long said she has no interest in running for office, although she held a few campaign-style rallies before the midterms urging people to register to vote.
And while Trump suggested Obama left him with "old and tired" military equipment, Harvard University professor Matthew Bunn noted that it was Obama who, in 2015 "laid out a $1 trillion plan to modernize every aspect of the US nuclear arsenal over the next 30 years".