Hrm... That makes no sense on many levels.

Logically I wouldn't think that a human female pregnancy hormone could affect a plant.
Second, if by some miracle the hormone could affect a plant... how would the seeds be receiving such hormones? osmosis through the shell?
Third... Why waste good birth control?

Really, med-user, you're not the first person to want to have all-female seeds. If there was such a simple way to do it, then don't you think every grower would be doing it? Just plant several seeds, and toss the lads as you find em.