Christian,
Honestly, I don't know of any one thing that helped me carry my first pregnancy to term. I can say that my OB was concerned from the beginning that I would deliver early. She was sooo sure that I would not make it to full term (which anything after 37 weeks is considered term). As far as my health history goes, I've been a pretty mild case most of my life (diagnosed at 9 mos old) until my mid 20s, where I've come down a little. My first hospitalization was when I was 19 and I've gone in about once a year or so since then (give or take 6 months). At five months pregnant, 23 wks, I went into the hosp for a clean out. It had been a year and a half since my last one. We ( me and cf docs) decided to act early at the first sign of me not feeling well and pft's slipping. From then on, I proceeded with a normal pregnancy. I started dialating at 36 wks (1 cm) which my OB said was normal. I dailated 1 cm each week until Ian was born (2cm at 37 wks, 3cm at 38 wks and went into labor the next morning). The only reason my OB thought I wouldn't carry to term was the cf. I have to tell you that I was her first cf patient and that she was not very comfortable or sure of what to do with me.
I have switched to another OB since then who is also new to cf but is very caring, pro-active about my care and willing to learn and do whatever she needs to take care of me and the baby. I am also seeing a high risk OB who has worked with other cf patients at my local cf clinic. The clinic referred me to her and I love her, too. She is great. It is too bad she was not here the first time.
Sorry, I kind of went off on a tangent. Back to your concerns. Don't let it worry you too much about delivering early. Yes, it is a possibility. But, it is also a statistic. We cfers know that statistics do not always apply to everyone. We are beating the odds every day! You have done a good job staying healthy and that will go a long way in this pregnancy. Keep doing what you are doing and don't lose any sleep over it. Eat healthy, exercise, do your meds and get good sleep. I personally did not think that I was going to deliver my son too early and I was right. Good luck to us both and enjoy this time. I hope this helps you feel better.