You have to support your children, so yes. We have a few friends that are gay, and whilst they have told there parents now, the lead up to telling them was quite stressful. As it turned out though they had no need to worry. In fact one of our friends has an even better relationship with his mother now that he is so open and honest about his situation. His only problem now seems to be his relationship with his partner, who I feel is just using John's emotions. This can happen in any relationship, but it's sad to see one of your friends getting used. (Carole is quite forward about it and has told him to leave him on numerous occasions )
I guess if your partner is one you really want to be with, then you should introduce her to your Mum. You will probably be pleasantly surprised in the love and support she gives you.