We had our first, and most likely only, child last October - our adorable daughter. I had hyperemesis my whole first trimester and lost 17 lbs, in and out of the hospital (and on disability at work). There's about a 95% chance of that happening again in future pregnancies - it could be better, or it could be worse.
Additionally, I had HELLP syndrome and apparently there's about a 25% chance of that happening - which is too high for me when that means my life and the baby's life is at risk.
I did EVERYTHING right - I was a very healthy weight (never had weight problems, thankfully) ate well (mostly ;) ) before and during the pregnancy (except the 1st trimester when I couldn't eat), I took my prenatals starting a year before we conceived, I read all the pre-pregnancy books and followed all the advice. It just goes to show that there are many things that are out of our control!
Additionally, our daughter was born with Beckwith-Wiedmann syndrome and had to have an omphalocele repair. Without going into too much detail, B-W syndrome is an overgrowth syndrome that puts her at a slightly increased risk of developing certain types of childhood cancer. It doesn't affect development and you can't tell if a kid has it by looking. If you're curious you can Google it - but some people may find omphalocele pictures a little disturbing.
Genetic testing revealed that there is no increased risk of future children having this, but still, going through that pregnancy was intense, and I'd be worried of anything else going wrong in future pregnancies.
Due to my HELLP syndrome, our DD was 6 weeks early and, because of that and her surgery, she was in the NICU for 4 weeks before coming home - which was not easy.
Long story short, if we have any more kids, we'll be adopting.
Edit: oh, I also had terrible postpartum depression and panic attacks due to PTSD from the pregnancy (had to spend a week in a mental hospital) and I don't think I could go through that again, either.