I didn't even know yet, but when I declared to a friend over dinner that I didn't think I would make a good parent, like you stated in your post, and had decided that I would not have children... I was already on the way. And single.

I am a parent of an adult child. My bpd really did affect the parenting I provided, as it affected the parenting I received. But.. I was not in any kind of treatment until my son was a teen and needed treatment. We both ended up on medication and therapy, although he could not (would not) participate fully in therapy and I was not in helpful therapy (or not ready for therapy) so the help was minimal. Knowing the depth of the issues now, I fully believe that if I had been in therapy during my parenting years and that support and modelling, I could have been a better parent.

Still, what exposure we did have, helped our relationship and every holiday and birthday he writes lovely and meaningful expressions of appreciation for my parenting in his own words. It amazes me often that he doesn't despise me (as I did my mother, pure projection here.)

He still struggles. I still struggle. I think the dysfunction of bpd existed for several generations before me and has been passed down to another generation. I think if I had been in therapy that could have been avoided. Passing down misperceptions and twisted thinking is inevitable, but I think therapy for each of us could have helped us both with that.

Support is good for any parents. Many get that from the close relationships with family and friends, something I didn't have much of because of my inability to form close relationships. But for most of his formative years, we lived in a really friendly and supportive neighborhood and my son had a great bunch of kids to be friends with. That was really good for both of us.

There is also this: when I had another person to look out for, be responsible for, it also gave me something to focus on outside of myself and a tender relationship that I'd never had. Being a mother gave me a sense of purpose and identity. I was good at infant mothering and loved it; it got harder when my son grew and became more complex. Now he is grown and lives far away, and I feel the lack of identity again.

Well, an early morning ramble I guess. I don't know that bpd should preclude a person from being a parent. There is much joy and fun and fulfillment in parenting. Even the best intentioned and non-bpd parents screw up and don't have the advantage of the knowledge we have gained in our treatment and self-exploration.
It is hard, I guess, to write about this with the perspective I have now, that is different than when I was young.