Just a thought, but with the Tardis unsure if Amy is pregnant or not, is it possible that the embryo is a Silent? Has she been impregnated "Alien" style?

If it was a Silent in there, then at first it would be seen then it would be forgotten. Not being human the Tardis may get stuck in a loop of seeing it then not seeing it.

Don't forget, when she was held captive by the Silents, they said she'd been with them several days and that she had been asleep/unconscious (forgotten the exact detail).

That'd certainly be Interesting...

They DID imply that she had a part to plan in their plan...

I love this idea! It would explain the Tardis' indecision too!

that is an interesting idea!

damn this arc is intense....love it!