Grapple Saving Throws

Does you roll the saving throw to resist being grappled, at a disadvantage if the creature attempting the grapple is 2 sizes or more larger? For example, a Large creature grappling a Medium creature. 

No since the rules don’t say so and it would significantly buff a lot of larger creatures with grapple abilities like the Purple Worm.

This would be absolutely brutal for a character that is neither Strength nor Dexterity based. Your poor Life Domain Cleric would have almost no chance of breaking loose if he gets grabbed. Don't use that rule.