I'd do it early, I get a few people call me as soon as they are pregnant, and some around 13 weeks. Of course you get those last minute ones too who have a last minute freak out LOL but earlier is better as Doulas need to plan everything 9 months ahead of time

Plus more time to get to know your doula. Most doulas only do 1-2 births a month due to family commitments so they can book up quick.
__________________
Kelly Winder
Creator of
BellyBelly.com.au & the
BellyBelly Pregnancy Centre
Birth Attendant (not taking new clients for 2008/2009) and Single Mum to Two Gorgeous Children
"Ante-natal care has degenerated to antenatal scare. There has been far too much focus on the worst-case scenario to the point where our thinking has become distorted and we've lost sight of normality." -- Dr Andrew Bisits, Director, Obstetrics Unit, John Hunter Hospital (Newcastle).