Caffeine is a vasoconstrictor if memory serves... And I wouldn't personally have any concerns about drinking it during labor regardless. But I know when I labored with my daughter my stomach was a bit touchy. I never felt really sick, but not much seemed appealling either, and while a long labor, I ate very little. For me, black coffee, and especially black teas, are pretty harsh on an empty stomach, so I just really doubt I'd want them during labor (although I'll ordinarily partake of either.) On the other hand, sounds a heckuva lot better than throwing up orange juice, which is beyond gross to me in the reverse direction, LOL.