Not technically breaking the rule

Lucy and Natsu have a drunken one night stand the night Lisanna returns to the guild and the next day Lisanna and Natsu start dating, but six weeks later when Lucy starts getting morning sickness. She knew that she was pregnant but she couldn't tell Natsu because he was with Lisanna and she had told Lucy that if she went near Natsu and the guild again that she wouldn't even live long enough to regret it, and that scared Lucy so she hadn't been to the guild since. That was a week ago when Lucy wasn't sure if she was pregnant or not, and nobody had came looking for her until she had already moved.