How do I deal with my wife's revelation that she doesn't want children?

Hi, I’ve got a problem I don’t know how to resolve…. I’ve been married since Dec ‘08. I’ve been with my wife since college, which is about 12yrs now. Before tying the not we were very sensible about things, discussed all the important issues etc. However, my wife dropped a bombshell last night. At first in our relationship we had both said we didn’t want any children. However, about a yr before we got married I explained to my then fiancée that my feelings had changed. To my delight she said hers had to but she hadn’t wanted to say anything. Last night, however, she told me that she had changed her mind & could no longer see a place for children in our future. I’m sure you can appreciate that I’m slightly shell-shocked by this change of heart & don’t know what to do. All I can think right now is that I either have to go along with this, or leave. I would greatly appreciate any advice you can offer. Thank you.