[conservababeJen]

At this very early stage it could prevent pregnancy before there is even an identifiable gestational sac

Which happens at 6 to 10 days, so at 2 weeks (14 days) it's too late.
eh?

[SarahW]

No. You can't presume she conceived instantaneously upon capture.

Conception typically doesn't happen the moment you have sex. In fact, it can take days from sexual contact for actual conception to occur, not even addressing the fact She might have ovulated days after capture.

It COULD prevent pregancy prior to there being an identifiable gestation sac.

But even if implantation were BEGUN, that is not the same thing as completed. These drugs do interefere with implantation.