Guavas and others who have posted about drinking, the NHS guidelines are definitely that you should have none at all and have been for a few years now, although personally I don't feel this is very widely publicised and different websites (as well as different health practitioners) say different things.
Whilst I really don't want to sound judgemental or worry anyone that has already had the occasional glass of wine (and I am guilty as charged as I had a rather boozy night out just before I found out I was pg), I do take quite a strong position on the subject. Through my work I have had quite a bit of training on the effects of alcohol on the unborn child. It is true that most children who get foetal alcohol syndrome do have mothers who have real problems with alcohol, but the only real consensus on the matter is that it's a complete lottery - one child's mother could have 10 pints a day throughout and be absolutely fine, whilst another's could drink fairly moderately and be severely affected. In all likelihood, a single glass of wine over Christmas dinner would probably do no harm at all, but personally I have decided not to risk it, especially in this delicate first trimester when everything is developing at a rate of knots.
Hope I've not offended or panicked anyone, but just felt I needed to say all that!
Have a good day, all 
9+6