I asked my OB about this JIC I was to need an C/sect I'd request getting that done too, and he said he doesn't like to do them as they have a higher failure rate. Something to do with everything down there being larger than normal and the ends of the tubes finding eachother and rejoining.
I'm sure he said that the failure rate of tubal ligation done during a c/sect was about 1:100 but if done 6 months post birth it is 1:600.