I made this mistake. My best friend can't have children, and her first failed IVF attempt coincided with the birth of my first child, more or less.
She asked me to come round, without the baby, for a bit, to talk about anything other than babies.
I had a 3 week old (or something like that, he was tiny) at home and while I totally intended not to mention him at all, he was in the end all I talked about. I honestly didn't mean to, but my life revolved around him at that point.
She didn't say anything at the time, but a bit later when she was feeling better, she got in touch and told me how I made her feel. I felt terrible. Of course she didn't want to hear about my baby, and despite my best attempts I had completely railroaded her.
I apologised, and made a much bigger effort not to talk about him if needed. We do talk about him of course (he's 7 now, so it wa a while ago now) and she is his Godmother, as it goes.
She is in the process of adopting, but if she wasn't, then I would continue to avoid talking about babies and stuff even thought that leaves little for me to talk about sometimes (I have a very dull life).
I am sure your friend didn't realise that she brought the conversation round to her pregnancy so much, she may simply not have thought about it at all like that. If you don't feel you can talk to her, can you perhaps write her a letter? Tell her that you're really pleased for her etc but that you're hurting and perhaps could she dial down the baby talk for a bit, especially at this time of year?
Honestly, when my friend mentioned it to me, I only felt bad that I'd hurt her. I was in no way offended, and I would hope your friend feels the same way.