I'm all for moderation, and I'm not about to berate someone for the (very) occasional drink during pregnancy.  But there are also very good physiological reasons for total abstinence during pregnancy.  For instance:  

Alcohol readily crosses the placenta, and is found in the same concentrations in both maternal & fetal bloodstreams.

But the fetal liver cannot break down alcohol, so it persists in the fetal bloodstream much longer, increasing the duration of exposure.

Although the worst effects (such as Fetal Alcohol Syndrome) are seen with heavy, repeated exposure, effects continue to be seen at lower doses.  At this point there is no known threshold below which you see absolutely no effects of alcohol exposure.

At least in the US, the medical community (e.g. American Academy of Pediatrics, American College of Obstetricians and Gynecologists, Surgeon General of the US, March of Dimes, etc.) is unified in recommending total abstinence.

Of course, every woman needs to make her own informed choice, and moderation may be fine for many women.  But you should at least be aware that there are genuine risks involved.

When I was pregnant many years ago with my first (1989), I asked my OB if I could have one drink for my 21st birthday.  She told me yes and then told me no more.  She said drinking in moderation wouldn't harm the baby, but moderation differs from one person to another.  For one woman, moderation might be 4 glasses of wine a day, for the next, it might be 4 glasses of wine a month.  It was easier to just say--just say no.  

And Renee is right, no one knows just how much alcohol can cause problems.  

I did take communion and went to a wine tasting with my third, but I think I had one taste of wine.  

To each his own, but why risk it.

My wife was actually told by the nurse that she should have a small glass of wine at night to relax during the 3rd trimester.

Most women I know have said the same thing.

The people that freak over it are generally men.  We've been beaten with the idea that it is the worst thing a woman can do while pregnant that we go a tad overboard.

Personally I was glad when my wife took the advice, it helped her relax and it didn't make me feel as bad about doing keg stands in the livingroom.

Wow! Times have changed.  When I was pregnant (35 years ago) my doctor told me to have a glass of wine or a beer every single night.  He said this reduced stress in the mom.  I am not a big drinker so I didn't take him up on that but I would have if I had been a drinker.  they also used to tell us that beer was a healthy drink.  Times have changed.

Folks in England aren't sure, but they've been telling pregnant women to stay away from them anyway (what

Folks in England aren't sure, but they've been telling pregnant women to stay away from them anyway (what