Children of Men is a violent but excellent movie about a near dystopian future where no children have been born for 18 years. No explanation is given for this premise, nor is one really needed.
As you might expect, the world is pretty down about this, fearing for the end of mankind after the current humans die in a way that doesn't seem to bother our current civilization (which is why science-fiction is the best of all metaphorical fiction genres, holding up a mirror to ourselves by changing something that we often take for granted).
The movie also presents the entire world as essentially reverted to barbarism, with the lone exception of Great Britain. But GB doesn't get off easy. They have their hands full beating up, killing, or throwing out the waves of illegal immigrants trying to get in, as well as handling the roaming gangs of thugs in the countryside who are out for a bit of the old ultra-violence.
Theo (Clive Owen) plays a man going about his business who suddenly gets "recruited" by an old girlfriend (Julianne Moore), a "terrorist" leader: she needs him to help smuggle a young woman out of the country. A young woman who is mysteriously, and miraculously, pregnant.
Along the way we meet violence, a bit of friendship, more violence, betrayal, more violence, and more violence.
Theo is an anti-hero. He does what he has to do while the forces around him are slowly circling in, but he's fragile, weak, and scared. Lots of people beat up, slice, or shoot people in the film, but he's not one of them. As a result, you feel the fear along with him.
While I disagree with the need to show so much explicit gore (not excessively much, but too much anyway), the movie is beautifully shot with many very long single shots, which gives an air of reality to the narrative.
As far as the pregnancy goes, this is just as unexplained as the premise itself. Nor is any explanation given as to what exactly will happen with a single baby born into this mess of a world. Which is all to the good.
Some people said that the best sci-fi movie of the last decade was Gattaca, but I disagree; Gattaca was an good premise but a rather poor movie shot with little flair and too tightly wrapped up. This is far better; better movie-making, and better story.