Speaking to TV Guide, Drew confirmed that Cristina will discover that she is pregnant.
"It's going to create a huge amount of drama between Cristina and Owen," she said.
"It became clear a few episodes ago that he was really excited to have children and she was like, 'Are you kidding? Do you know me? No, never'. That is going to present a huge issue in their relationship and marriage."
Drew also suggested that Meredith's decision to tamper with the Alzheimer's trial will have a big impact on the characters. She has said that Alex will face consequences for telling Owen about Meredith's behaviour.
"Last year, the finale was about something external coming in and forcing our characters to cling to one another for dear life," she said. "This finale is about something internally that implodes and ends up breaking relationships and tearing people apart."
Drew explained that there will be "drama" when Cristina finds out what Meredith did and that Derek will also be unhappy about the revelation.
She added that the characters will find out who has been made chief resident in the episode and suggested that April still has a chance of getting the role.
"Alex has just tattled on Meredith and she has just screwed with the Alzheimer's trial, but there will still be tons and tons of drama associated with this whole run for Chief Resident," she said.
The season finale of Grey's Anatomy, which Drew has previously said will "shock" fans, airs tonight at 9/8c on ABC. In the UK, the show continues on Wednesdays at 10pm on Sky Living.
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