Yes it can cause SIDS amoung other problems, basically when u smoke ur baby is smoking not cool!
Are you smoking cigarettes, weed, or something else? Cigarettes most definitely do affect the child, it can kill it or cause serious health risks.
Yes smoking make a baby high risk for low birth weight, premature delivery (which includes all the risks associated with premature babies), and potentially higher risk for ADD and ADHD, obesity, and maybe even miscarriage. Also second hand smoke is bad too; children who grow up in a house with smokers are more likely to be sick and have asthma problems during childhood than those who live with nonsmokers.
I know how hard it is to stop smoking, but you have to do your best. Try to remove yourself from people who smoke, if they live with you ask them to start smoking outside. (Especially if they will still live you after the baby is born. Second hand smoke can kill.) Right now, even if you can't give it up fully do your best to cut it down.