They say October has the most birthdays of any month. In fact October 5th is the day with the most births. That is not hard to imagine considering that February is the conception month. When it's dull and grey and there's nothing to do well... babies are conceived.
Its something to think about when writing your characters-whether you set it in February or October.
What else causes a bump in births? Blackouts. Blizzards. War? Can you think of more? Cheers~