Tbh I dunno. The research I read just said they couldn't really seperate the two, not enough people take it before being 40wks to determine this. Sounds dodgy but have a scout round google, I try and have a look on google scholar so you get research papers rather that forums etc which give people opinions etc.
At end of day it's another one of those things where it's up to you if you want to risk it. Xxx