No, drinking pineapple juice will not induce labor. The main ingredient in pineapple, which is thought to increase the chances of both conception of pregnancy and spontaneous labor, is called bromelain.
Scientifically speaking, a woman would need to consume a total of 7 pineapples to take in enough bromelain to induce labor. The highest concentration of bromelain is contained in the core of the pineapple.
Due to the way juice is processed, most commercial brands of pineapple juice break down the bromelain to barely perceptible levels. Fresh pineapple juice would, however, contain higher levels of bromelain.
In most cases, though, natural methods of induction will not work unless a woman’s body is ready for labor. Even medical induction often fails if the mother and baby are not ready for birth.