I am very passionate about natural childbirth, and when I start talking, I don't have an easy time restraining my strong feelings about some things, lol. But having said that, I'm realizing a few things:
It's important to be in the conversation in a way that will minimize defensiveness (which is what it sounds like you want to do). I try to make it known that I have read/researched a lot, own books on the subject and know the local scene as far as birth centers, midwives, doula practices... So that an interested friend knows she could ask me if *she* wants the conversation.
If we are talking about a previous experience of hers, I try to remember the good advice of looking for *some* positive thing to say about a way in which she *was* strong, positive, proactive, etc. Esp in a negative brith experience (which as we know could have been natural or interventive!), it's important to pull out the positive aspects in it -- to look at anything you would like the same. The to build on that, ways it could be different.
If I could get one thing in, it would usually be a referral to something specific that has more ifo than I could ever share in a conversation. Like:
'Hey, I have X birth video at home, which helped my dh feel more relaxed about how birth can go right --would you want to borrow it?'
Or, 'I loved reading whatever I could when I was pregnant! One great website I stumbled on was maternitywise.org.'
Or, 'I have heard such neat things about __ who is a Bradley (or whatever) teacher. Lemme know if you want her number.'
Or I would lend someone The Doula Book.
I wonder, if you feel out the pg coworker for example and she seems open to conversation about epidurals, you could throw in a little known factoid, which might make someone wonder what else they haven't been told. I often share my frustration that more people don't know that epidual anethesia raises maternal temps, leading often to newborn workups for infection. I emphasize that every woman should be able to make her choices, but that I wish care providers were stronger on informed consent. I feel like that puts the emphasis on the care provider's burden as educator, not the Mom's ignorance. Does that make sense?
Anyway, just wanted to say it's something I'm constantly trying to figure out. I'm turning 30 this year, so friends all around me are getting pg. And just having completed doula training makes me a dangerous person to talk to!