I've been on Celexa for a little over a year and a half, and am 19 weeks pregnant. I had the misfortune of having to switch insurance and therefore doctors (since the prior doc was thru an HMO) right when I got pregnant. I had to start all over again with finding a dr to prescribe Celexa for me when my refill ran out (I'm using midwives for the pregnancy that can't prescribe drugs).
I found that I really had to stick up for myself on this one, because most doctors and nurse practitioners know SO LITTLE about SSRIs and pregnancy. When I first went in, the dr had only just looked it up briefly in a book before she came in, and was concerned based on the blurb about pregnancy, breastfeeding, and Celexa. She said it wasn't so much the pregnancy part that worried her, it's Celexa and breastfeeding newborns. She was just going by the classification it gave, not any *real* information on the subject.
I had to go do my own research and bring it back to her. I was able to find Dr Hale's book "Medications and Mother's Milk" at the library, and some articles & studies online, some linked via Kellymom.com. The problem is that there has been so few official studies on various medications and breastfeeding (particularly because bf'ing is not much of a moneymaker for any company to help fund studies), so there's not a whole lot of concrete information. However, all of the anecdotal evidence points towards Celexa being pretty safe during pregnancy and breastfeeding. Dr Hale put it third on his list of preferred SSRIs, behind Zoloft and Paxil (though this was back in 2002). However, Paxil has been more recently discouraged in pregnant mothers (and I personally didn't have the greatest experience with it). Zoloft seems especially hit-or-miss with people, and I personally was scared to try and switch to it.
The bottom line was...
My midwives AND the nervous dr I saw did all agree that it's better to be on something if you need it, rather than subject your baby and yourself to a flailing anxious or depressed mother. And that's really what it comes down to. Nothing that I read made me think that taking the chance to go off of it or even switch was the best thing for me and my baby. That's not to say that they won't have any of the drug in their system, but it's such a negligible amount that it doesn't really seem to concern any professional that actually knows anything on the subject. Lower doses are of course best, so I would definitely recommend to try a low dose for at least a month to see if that does it for you. I'm on 20mg of Celexa, which is the starter dose, and has been the difference between functioning and not functioning for me.
Anyway, that's my experience and my two cents. HTH, and best wishes to you.