MYTH: Alcohol or drugs taken after the first trimester will not affect the unborn baby.
FACT: Most organ development is completed a few weeks after the first trimester. Brain development continues throughout pregnancy and after birth. Exposure to substances any time in the pregnancy can affect the baby’s brain.
MYTH: One drink in pregnancy is enough to harm the unborn baby.
FACT: A safe amount of alcohol in pregnancy is not known. It is unlikely, though, that a single drink before a mother knew she was pregnant could damage her unborn baby.
MYTH: There is no hope for a baby exposed to heavy drug and alcohol use.
FACT: There is always hope. Drug and alcohol use in pregnancy affects each baby differently.

Source: MOTHERISK, http://www.motherisk.org/women/alcohol.jsp#two