What affects does a pregnant woman have on her baby if she smokes?

Marijuana:

• Common slang names: pot, weed, grass and reefer
• What happens when a pregnant woman smokes marijuana? Marijuana crosses the placenta to your baby. Marijuana, like cigarette smoke, contains toxins that keep your baby from getting the proper supply of oxygen that he or she needs to grow.
• How can marijuana affect the unborn baby? Studies of marijuana in pregnancy are inconclusive because many women who smoke marijuana also use tobacco and alcohol. Smoking marijuana increases the levels of carbon monoxide and carbon dioxide in the blood, which reduces the oxygen supply to the baby. Smoking marijuana during pregnancy can increase the chance of miscarriage, low birth-weight, premature births, developmental delays, and behavioral and learning problems.
• What if I smoked marijuana before I knew I was pregnant ?According to Dr. Richard S. Abram, author of Will it Hurt the Baby, "occasional use of marijuana during the first trimester is unlikely to cause birth defects." Once you are aware you are pregnant, you should stop smoking. Doing this will decrease the chance of harming your baby.