Yes, she did get pregnant

Your stepmom has been fucking you for nearly three weeks. While you went out to get some shopping done, Christine took her pregnancy test and got a positive result. Smiling to herself she put the test away in her underwear draw and awaited your return.

As soon as you walked through the door, Christine grabbed your arm and dragged you upstairs, closing the door she showed you the test results. You smiled and hugged her, gently kissing her forehead. "Now that you're up the duff, I think its time for my step-sisters as per our agreement."

Nodding Christine said "Leave it to me, at the moment only Britney's at home so I'll wait for her sister to come home and then we'll tell them the news."