This is a very common question. Although alcohol is known to cause growth problems and mental retardation when the mother uses alcohol is excess (fetal alcohol syndrome), the exact amount needed to cause problems very early in pregnancy has not been determined. I go by the “All or None” philosophy. Either so much was used prior to the patient knowing that she was pregnant that it leads to a loss of the pregnancy (ALL) or no harm comes to the pregnancy (NONE).
Obviously, once you know your pregnant, you need to stop drinking, but I rarely see a problem when it is done prior to the first 6 weeks of pregnancy. In fact, drinking too much is usually how you got pregnant in the first place. 🙂