Speaking from my own shores experience, people are getting married because they had the kinds so young.
Nothing makes me smile more than seeing a pram pushing couple. The screaming bastard, writhing in his own soiled nappy and the faces of the parents, defeated, destroyed human beings, knowing their own futures are now gone to the fact they were irresponsible in a night of passion. (Passion being latin for 3 minutes of disapointing premature ejaculatory sex)
Even then, knowing their one night stand means they are forever linked, married to one another since no one else will want a single parent. I sure as hell wouldnt raise another mans 12lb mistake, nor do I see any woman being enthralled to be with a guy who on weekends has to babysit a child he has as much affection for as a throw pillow.
The best situation is when you see the above, on top of which, the pale faced, sleep deprived possibly drunk mother has the tell tale signs of a second baby bump!