From what I've heard the enzymes causing labour are only in the core of a raw pineapple and you need to eat about 15 of them. Otherwise I drank pineapple juice all the time throughout my first pregnancy, even freshly made whilst on holidays, and its a great drink but no labour.
I read that it helps too. I tried it with my last son. I ate an whole pineapple and the only thing it did for me was make my mouth hurt from all the citrus. So I guess it depends on the person
Pineapple juice and the pineapple fruit made me go into labor but I think it depends on the baby