If you think a parakeet is pregnant how do you get it in a birdhouse?

You don't. Parakeets are birds. They do not get pregnant, as reproduction is done through the laying of eggs. The eggs take about three weeks to form properly in the body, but this is not called "pregnancy". They look the same when they are laying eggs as when they aren't. In other Words, birds don't "hold" their eggs inside their bodies and they do not show a big belly to indicate that eggs are on the way.

Birds which are getting close to laying an egg become more lively, excitable and playful. You need to provide it with a nesting box in its cage.