Thanks for the tea question! I would avoid green tea at all times during pregnancy.
The caffeine in green tea is a stimulant, and will transfer to the fetus.
To my knowledge, it will not bring on labour during a pregnancy, but it will send your baby into a caffeine induced frenzy. A nice cup of some safe Herbal Tea for Pregnancy would be a better choice.
Bringing on labour is not advised with herbs or medications. How about a nice long walk? Many people swear by this technique and the fresh air will do you and your baby some good.