Fetal alcohol syndrome
Doctors suggest that women who are trying to get pregnant should also drink no alcohol.  This is because a woman may not know she is pregnant for the first 4–6 weeks of her pregnancy.  Some women drink alcohol during this time, since they do not realize they are pregnant.  But drinking during the earliest part of a pregnancy can cause severe FAS because the earliest part of the pregnancy is when the fetus's brain starts developing.  This is why it is safest not to drink any alcohol if a woman thinks she might get pregnant.