If you are thinking about getting pregnant in the near future, you may want to start curtailing the volume and frequency of your drinking, so you can gradually adjust to the lack of alcohol that a healthy pregnancy requires.
If you drank before a missed period - not to worry, nothing can happen from alcohol until the embryo implants into the lining of the uterus. Once you miss a period - no more alcohol.
Can you occasionally have a sip of wine at a party, or a half a glass of champagne at a wedding - yes. We will allow one glass of wine for cramping associated with amnioscentesis in the mid trimester. We will not allow any regular drinking (not even a glass of wine with dinner on a nightly basis), and we tell you to make sure to avoid binge drinking - even once. There is no safe threshold for alcohol in pregnancy - say no to anything but the abovementioned sip.
The worry with alcohol in pregnancy is fetal alcohol syndrome (FAS). FAS is the most common cause of preventable mental retardation and developmental problems in babies. If you have a drinking problem, speak to your doctor well before you want to conceive, so you can get the appropriate treatment and completely discontinue and stay away from alcohol throughout the entire pregnancy and beyond - it's an investment for the future in the brain and health of your baby forever.