37 weeks and have had 19 hours of diarrhea. Normal or not?

It's best to talk to your midwife anyway. I had it for 5 1/2 days, and had to be on IV fluids on the 3rd day b/c I was dehydrated despite being able to drink lots of water. I had some braxton hicks because of the dehydration. Of course that's just my experience, but just wanted to put it out there that it could be something other than early labor and to keep an eye on it if it persists. Good luck!