I'd trust your gut. I had the feeling this whole pregnancy that this baby was going to be smaller than my others, and she was! 12 oz smaller than DS and a full pound smaller than DD. So if you aren't measuring bigger and have a feeling baby isn't as big, then I wouldn't stress. That being said, I really don't believe that a S&S will do much if your body isn't ready anyways. So of you are teetering on the edge of labor, then it might work but if you're a good ways out I don't think it will make much of a difference.