I am breastfeeding. My son is 1 month. I'll be honest it's been challenging at times but totally worth it. I'm so glad I've stuck with it. It's been a great experience thus far and it's only getting easier by the day.
Do get the book that Wanderlost recommends just in case you need it. Also, locate a weekly bf'ing discussion group that you can attend once the baby arrives. Take a breastfeeeding class before the baby arrives. A good book to have on hand for trouble shooting is <i>The Nursing Mother's Companion</i>. FInd a lactation consultant before you deliver so that when you are home you can give her a call to pop over and help you by observing your child's latch, etc. You won't have time to be calling all over town and figuring out your insurance coverage once the baby arrives.
I gained a good amount during pregnancy - 27 lbs. - so nutritionally it has been possible. You must be dilligent about eating healthily and having additional calories as your weight requires. You will be very scheduled between caring for your cf, feeding yourself and your baby. It's nearly a full time job - no joke!
My son was born on 7-10-07 weighing in at 7 lbs. 10 oz. Yesterday he weighed in at 11 lbs. 1 oz. so I feel confident that I am providing nutritionally just fine for him.
I do not think bf'ing is encouraged enough in the US. Jo is probably not from the US judging from the mum signature. At one point during my hospital stay a nurse woke me up and told me that I should feed my son 10 oz. of formula because he wasn't weighing enough?! WTF? She was so proud to show me how it was bedside right there in the drawer. I told her she could wake me every 2 instead of every 3 hours or bring me a pump that I would not be giving him any formula during this night that I would speak with a doctor in the AM. There were many apologies to me in the morning for the formula confusion. By the way, his weight was fine. He only lost 5% of his birthweight at discharge which is well within normal limits.
Each evening my husband feeds my son one bottle of breastmilk. We began this at 3 weeks of age. Son goes back and forth between bottle and breast and pacifier with no problems although we just give him the one bottle each day but when I return to work it will be all pumped breastmilk fed by the nanny during the day. I know a half dozen mothers that highly suggest adding the bottle in week 3 or 4. Some of them waited until 6 weeks with their first and they dealt with attitude from their child. Also if you must return to work at 6 wks (which I highly recommend you don't - try for 12 weeks) it's a bad time to make a big change. As my lactation consultant said, "You can add a bottle once there are no issues with breastfeeding and it it totally well established."
I think it's good to give it a try but if you are underweight with or without the pregnancy I don't know that it is a good idea. I say this because for me weight is critical for me to keep my lungs healthy. It is for this reason that I really believe Melissa did the right thing because it is my understanding she was underweight.
At this point, focus on a healthy pregnancy with a weight gain of 25-35 lbs. Many cf moms have difficulty achieving this which I think can set you up for breastfeeding challenges. If nothing else, at least it's one less bone for your doctor to pick at. Oh and I will also agree that doc's are clueless about bf'ing.