How much can I drink if I am pregnant ?

No safe amount. There is no research that has identified a 'safe' amount of alcohol in pregancy. You have to consider that everything you put in your mouth, you give to your baby. So it's probably better to abstain while pregnant.
A bit. The official position of the american college of obstetricians and gynecologists is that you don't drink at all in pregnancy. There's no data, however, to suggest that minimal alcohol intake is harmful to a baby. In europe light alcohol intake is not discouraged in pregnancy. Fetal alcohol syndrome is associated with heavy alcohol use. The official line is no alcohol at all.