Lohan, 27, said it happened during a break in the filming of her reality show "Lindsay," on Oprah Winfrey's OWN cable channel. Lohan revealed the personal information during the show's season finale Sunday.
She explained that was the reason she reportedly held up production of the series, adding that she was sick and unable to move.
Lohan began taping the OWN reality show shortly after leaving her sixth stint in rehab last summer.
The actress didn't offer any further details about her ill-fated pregnancy.
The Associated Press contributed to this report