TTA, good job handling yourself in that convo with H! You didn't rescue and that's huge.
I know moms can guilt us so easily but you should DB her. Listen and validate, "I understand how you could feel that way." Remember that it's her issue and you can't control or fix it.
Establish some boundaries and maintain them. "Mom, I understand that you're feeling sad right now. As you know, things are difficult for me right now. I need to focus on myself and my marriage and cannot even think about children at this time. I like spending time with you and talking with you but I will no longer talk about children. If you continue to bring it up I will excuse myself."
As a happily childfree person, I declared early on that I was not going to have children and at the time my mom was fine with it because her standard line was "You know I'm too young to be a grandmother." As the years went by she told me that I would change my mind when I met the right person. I set her straight and let her know that it was not going to happen and I would simply not talk to her anymore if she continued to bring it up. I'm not sure if she believes me now but it hasn't been discussed since then, many years ago.
If you love somebody, set them free. http://tinyurl.com/2empx2g