We are also Jewish and expecting a baby in July. I told my family last week that if it turns out to be a boy we will not be circing. My mom got a little cold about it, but accepted it. She warmed up to it after a long discussion about things. We talked about how Jews are finding many ways to make males and females more equal, even when it goes strictly against the bible (think of how your ketubah now allows you to end your marriage and not just your husband).
What if you told your mom that in an effort to make females equal to men you decided to circumcise your daughter, if you have one? My mom was mortified at that thought, and I explained to her that now it was time for males to be given the same right to bodily integrity as females. I had to have a bit of an anatomy lesson with her, which was slightly uncomfortable. I think as a culture we are so used to the term "foreskin" and think of it as just skin. I really taught my mom about the function and purpose of a foreskin, and how it is attached, and that was a major eye opener for her.
As Jews, we use symbolism for many things. For instance, did you mom sacrifice an animal on Passover? Likely not. I'm sure she had a symbolic shank bone on her seder plate instead. It is time that we started giving our sons the same bodily integrity that we give to our daughters. There is no reason that we can't offer a symbol of our covenant with god to replace the barbaric practice of permanently removing a healthy and functioning part of their organs.
Does your mom keep strict kosher? Honor the sabbath? Do you? How will not honoring those impact the Judaism of all involved?
The truth is, your child will be Jewish because you are Jewish. Male circumcision is not a requirement to being Jewish.
It is a shame that your mom waited until this point in your pregnancy to dump this on you. When you are comfortable with it, maybe sit her down and go over some of this stuff with her. Maybe now, so she will attend the naming ceremony, but maybe later. Do it when you feel capable of a calm conversation with her, when you are in a place that you can walk away if you need to.
I don't know your mom, but I can't imagine that she will just walk away from you and her grandchild over this issue. She might miss out on an important milestone (the naming), but I can't imagine it will be permanent. We are fighting a very long held system of beliefs and way of doing things without question. It takes a lot to get our parents to open up to the fact that their thoughts on this subject might be wrong. Especially if you have a circ'd father or brother.
Hang tough! You are not alone. Times are changing, slowly but surely. Someday, circumcision will be something that is performed symbolically. And it will be because of parents like us, who stood up for our sons and had voices that were heard. People are listening. I didn't come up with this on my own. If my first child had been a boy, he would have been circ'd (thankfully, we had a girl). But, I listened to what others were saying. And others will listen to what we are saying. It might take a while for your mom to listen, but she will calm down. And she might even start to come around.
Good luck and congratulations on your baby!