What does temporary pregnancy means?

Embryo withered: Nobody knows how many conceptions don't survive, but maybe it's 20% or 1 out of 5. The ones that survive long enough to implant will give a positive pregnancy test. An embryo that fails to implant doesn't cause a positive test. If a test is positive and then negative after some days, we can assume an embryo implanted and withered. A positive test could also be a false positive (no conception).