What stage of pregnancy is smoking and drinking the most damaging?

Would it be more dangerous to do these things at the beginning or the end of a pregnancy? I know that fetal alcohol syndrome for example is more damaging during certain months of pregnancy but I do not know which ones.

This is pure curiosity as a biology major.

Kate Moss to quit smoking for pregnancy

Kate Moss to quit smoking for pregnancy
British supermodel Kate Moss is trying hypnotic therapy to help her give up cigarettes so that she can start trying for a baby with her fiance, Kills rock band guitarist Jamie Hince.

Read more on Sify News

Smoking moms tied to lasting kids’ sleep woes

Smoking moms tied to lasting kids’ sleep woes
Mothers who smoke during pregnancy are more likely to have children with sleep problems from birth all the way through age 12, new research shows.

Read more on Reuters via Yahoo! News