I did this a few years ago - Christmas was coming and it was a definite maybe (eratic periods but a longer gap than usual). Enjoyed the Christmas spirit ... a little too much ... and bled. Thought I was due my period, but bleeding stopped and a few days later the little lines appeared :)
Baby was fine but looking back I feel dreadful. 
Christmas is coming ... there could be a slight chance of another maybe on the cards (although guessing not just yet)
So - enjoy the lead up to the festivities ... or test at every feeling sickness/pound gained to avoid drinking at a few weeks gone? 