How can I get up without waking up my girlfriend?

My girlfriend is in her third trimester of pregnancy so she doesn't get a whole lot of sleep. When I get up I always wake her up and she can't go back to sleep. Occasionally I need a drink of tea or to go to the bathroom and I wake her up getting out of bed. I normally sleep with my arms around her and she will hold one of them so I'm kind of locked in place. She's a really light sleeper and has had trouble staying asleep so I just want to make sure she doesn't lose any on my account. Any suggestions? Thanks!