I hired mine at 12wks and it was THE BEST move we made. It depends on the experience and personality. As said in prior posts, the earlier the better so you can find someone who has the experience and the personality that will work WITH you.
I had preterm labor my last pregnancy two days after I called the Doulas office. My experience with the hospital and medical staff was horrific and yet again, as high risk, I do not have options but to go to the SAME hospital and the same perinatologists office because there are no others locally to take me being high risk.
I want as natural as possible. I refused drugs during my last labor and hope to refuse drugs this time as well. The Doula has been a blessing and she's helping me to cope with the loss of our son while also the joy of our new baby. She has come up with a plan to deal with the medical staff, keep me out of the room I was last in, and keep the medical staff from intervening when I don't want them to "unless life or death for me or the baby".
I feel "safe" knowing there is someone to advocate for OUR wants and needs and it's the best investment we've made thus far.
Enjoy looking for Doulas. I bet you'll wreap the benefits. Had I waited any longer, my doula wouldn't have been able to take me. She's the most qualified and only takes a handful of patients because she travels the U.S. training other Doulas. I'm blessed to have her with me and am looking forward to my new experience with as natural an approach as I can get in a hospital atmosphere.