The affects of drinking alcohol while pregnant have been studied extensively.
There are two camps, one which maintains that even small amounts of alcohol is lethal for the baby and women who would like to get pregnant, are pregnant or are nursing a baby should completely abstain from alcohol consumption. The most lethal affect of alcohol consumption on babies is what is called fetal alcohol syndrome (FAS) which causes damage to the body and the the brain and adversely affects the growth and development of babies throughout their lives.
The other set of researchers have not been able to identify any direct link between light to moderate alcohol consumption and an increased risk of harm to the baby. The possibility of acquiring FAS is only in cases where the mother consumes excessive amounts of alcohol and is in a way addicted to it.