Her partner, Cyrus Sutton, an American professional surfer and filmmaker, featured in the photos.
Fellow Australian actor Teresa Palmer congratulated Lucas in the comments, writing: “Can’t wait to see you as a mother and for these little babies to be together. We love you guys xxx.”
Fans also wished Lucas joy.
“Another perfectly healthy and beautiful 40-year-old woman having a baby. Don’t let anyone tell you there is a deadline by 30,” one said.
Lucas was on Home and Away from 2003 to 2006, playing the character Tasha Andrews.
She starred alongside Chris Hemsworth, whom she dated before his Hollywood breakout, the Daily Mail reported.
Lucas previously had roles in American films such as Transformers: Revenge of the Fallen and Daybreakers.
In 2020, she made headlines for refusing to test for Covid while on the film set of Bosch and Rockit.
Lucas said on a podcast that she thought it was fine not to get tested because “my immune system has just become so solid from my way of life, how I live and eat and think”.
She had previously stated that she “doesn’t trust” vaccinations, News.com.au reported.
In 2020, she spoke at an anti-5G rally in Byron Bay about her concerns that the technology could compromise privacy and usher in “a regime of total surveillance”, the outlet reported.