Your partner is going to have a baby and you feel emotionally locked out. Granted you will not be fielding the morning sickness with dry crackers or feeling the fatigue or labor pains, but there are ways that you can feel part of the pregnancy. She is not trying to lock you out purposely; you just need to find ways to take an active role.
Many of these ideas will have you not only helping your partner but allowing you to feel more involved than you may have normally felt. The first important thing to remember is that you should ask questions. Be a part of the excitement and planning from the very beginning. Ask her when the baby is due and talk to her about her feelings. Help her make a list of things to ask the obstetrician.
After the first visit to the doctor, make it your responsibility to ask her daily if she remembered to take her prenatal vitamins and if she had enough rest that day. (But don't be a nag about it; just let it come up in normal conversation!) Read baby care books with her.
Make plans for the future of your new family. When the pregnancy is further along, discuss possible names and find out if you can do anything like helping to get a nursery prepared. There are certain things she will be under doctor's orders not to do, and those might include things like breathing paint fumes or lifting heavy objects.
Pamper the expectant mom. As the pregnancy gets further and further along, she may have lost the morning sickness, so ask if there is any food she is craving that will not make her feel ill like it would have done when morning sickness was a problem. (This is not necessarily accurate for all women. Some have "morning sickness" all day long and others experience it the whole 9 months, not just the first 3 or 4 months.)
In addition to asking if there is any food or drink you can get for her, find out if she would like a massage. Often in the later stages of pregnancy, a mom-to-be will experience backaches that a gentle rub may ease. Another problem is swelling feet, so a foot rub would be a gift she will adore if her feet have been hurting all day.
The main goal is to make and keep her comfortable. Would she enjoy a warm bath? Fill the tub for her. Maybe she would rather lie down and read a book instead of going to the grocery store which had been the planned activity. Ask her for a list of essentials and get those groceries for her.
Remember that at least during the last few weeks or months of the pregnancy, she may have trouble getting comfortable to sleep. If you can do anything to help her be able to catch a nap once in a while, she will be forever grateful.
One thing that she just may appreciate more than anything else is knowing that you are excited about the new arrival, too. If you want to be part of the pregnancy, make sure you are there for the not-so-pleasant happenings (aches and pains, nausea, insomnia, etc.) as well as the fun dreaming and planning.