How much interference can you tolerate and how much risk would you take?

You say this might be the last time you do this, so obviously it's important to get it the way you want it, if possible. BUt as Mel points out, none of us are psychic so only you can know what is tolerable and what isn't.

You could take iron (liquid is best to avoid constipation, though it's not cheap!) the last 4-6 weeks of pregnancy, and take calcium (which muscles need to contract - taking large doses in labour can be helpful too) for the same period, you could think seriously about taking a bite of raw placenta as soon as it appears, get a homeopath to prepare remedies for you to hasten the 3rd stage and work on foetal positioning so that this birth can be as easy as possible on your uterus. You could use clary sage inhalation in the 3rd stage to help the uterus contract...i could go on!

Or you could have a canula placed and not have anything run through it unless you are bleeding.

Or you could decline the canula and hope for the best.

I think you need to sit down seriously and work out HOW important a natural 3rd stage is to you. It doesn't matter if it seems a "little" detail to others, you need to be honest with yourself about how much you care about it. I hope to have 3 babies in total, and if none of them are freebirthed i'll be disappointed. I know lots of women go through so much and just want a live infant to take home after their labours, but i am walking my road, not theirs, and birthing a baby entirely on our own (DP and I) would be magical to me.

Work out how much it means to you, and from there you'll be able to work out how much you're willing to do or risk to get it.

Bx