I didn't get any with my first two, but I did get one a few days after my third was born. Didn't happen right away, which seemed odd to me. I honestly don't know if there's a way to prevent them, but I think what Amy said is bound to help - don't push unnecessarily hard, if you can help it. But, that baby's got to get out one way or another - don't hold back if you need to push, just to avoid hemorrhoids! I think that avoiding straining in the days right after birth is important too. Keep up your fibre and fluids.

If you get them.... get attention for them ASAP! I left mine for a while, hoping they'd go away, and they HURT SO BADLY! Mine was external, which is the nasty kind, I guess. Anyways, the midwife prescribed proctofoam which has a pain reliever, as well as something to help heal the hemmorhoid, and it was wonderful! If you end up needing it, see if you can get that stuff.

Hope all goes well at your birth!