I strongly believe pumping before hand with Paris enabled me to breastfeed successfully (before external interference) because even though I had PCOS and was borderline GD and had PCOS (apparently all things that stop milk coming in) my milk was in abundance by the second day. Seth whom I didn't pump for prior to his birth my milk didn't come in till 48 hours post birth.

If you're worried it can't hurt, providing its not too before EDD as it can cause contrax, and as my OB said to me if it starts labour that isn't the real deal and the cervix isn't ready it can cause problems in itself.