When I was 5 months prego with my second child, my mom moved to Nevada (from CA). I was so mad! How could she leave her only grandbabies to live in Las Vegas? Didn't she want to see them grow up? There were all kinds of questions and lots of emotions to deal with. I was in a crappy marriage and having another kid. All I needed was to be abandoned by my mother to boot!
So here I am 9 years later. Mom is still in Vegas. I am out of the crappy marriage. Everyone is much happier. I got over being mad when we got to go visit and she would come out here. And we actually (believe it or not) have a stronger relationship now than we ever had! We see eachother maybe twice a year but talk ALL the time.
The point is, everything happens for a reason. My mom told me that she left so I could live my life and not have her constantly stepping in. It was nice because when I left my husband, she was limited in her influence. If we had to have "face-to-face" conversations about it she might have been able to talk me into staying a bit longer (SHe hated my husband but thought at least being with him was better than being alone...she would have been WRONG!) She also doesn't get to criticize me for the way I raise my children and she can enjoy them when she does get to see them instead of feeling that she has to have a hand in raising them.
I know this has no real bearing on how to control your emotions but I thought a little perspective might help. To be truly honest, there is no real way to control your emotions while pregnant because your hormones are going nuts! Find yourself some distractions. Start scrapbooking pictures of your mother and siblings so that when the baby does come, you can both look at pictures and the baby will recognise them when you do see them. There are many ways to put a positive spin on this situation, you just have to weed through the emotions to find them. ;) Best of luck and congratulations!