As alcohol is a teratogen (i.e., a substance that can cause developmental defects), any exposure of the developing foetus to alcohol could conceivably result in untoward effects.  Those range from mild to severe, and there's unfortunately no way to correlate how much you drink with how severe the outcome.  There's just no "safe" amount, so if you drink at all, you're tempting fate.

That being the case, the safest course of action is to abstain entirely.  Trust me, you do not want a child with Fetal Alcohol Syndrome.