That's the thing that I don't get. If she was barren she must have realised straight away. The thing is that I don't think Igraine had fully come to terms with dying the way she did until she saw Arthur. If she'd have known she'd have had nine months to come to terms with it. Yet her feeling of betrayal from Uther and her statement that he "deceived" her suggests she didn't know until much later.

I look forward to getting to the bottom of this.