Short, efficient, psycho, suspense thriller.
An expecting couple living in a second floor flat find their new downstairs neighbors are also expecting.
Things very quickly get out of control, and while viewers who've had newborn babies may see that it is clear people's behavior is uncomfortably not what it is supposed to be, we also get visual clues of where the story is heading. Things don't really get spelled out till the end (which may have even been unnecessary, even then, but the movie does tie all lose ends) and the movie trusts us to pick up on the clues as they are presented.
Doesn't waste your time. Check it out.