On twitter I casually posted "Have you noticed that people usually give a weight when announcing births but almost never when announcing marriages or deaths."
webcowgirl pointed out, almost certainly correctly, that this is because birthweight correlates with infant mortality. I would be willing to lay money this is where the tradition comes from. But you know, in this day and age we can do better. I solemnly swear that should I ever have the misfortune to produce offspring instead of a birthweight I will announce thus:
"Accounting for birthweight, gender and age of parents, a cumulative distribution function for the infant's age at death is attached as figure 1."
See, if we're going to predict mortality, thanks to the wonders of science we can do better than just weight. I urge any prospective geek parents to try this, indeed I'll even offer to help with the graphing.
This is probably why I shouldn't have children (amongst other reasons).
Tonight I am packing glowsticks... alas, in a sad statement on my life right now, this is not because I'm off to a 2002 themed club but because I'm going to spend Halloween weekend underwater in a flooded quarry in Wales.