How does one deal with women who smoke or drink during pregnancy?

Some facts on both behaviors might be relevant. The March of Dimes has excellent references and statistics that may prove useful for your research.

According to statistics provided by the March of Dimes. Smoking during pregnancy can result in low-birth weight, premature birth, placenta praevia (low lying placenta), placenta abruption (placenta peels away from the uterine wall before delivery), and stillbirth. SIDS or sudden infant death syndrome is another risk associated with post-delivery infants of smoking moms. I did not find any information regarding how much tobacco use was considered safe for a pregnant mother.  So, we might assume that no levels of tobacco use are safe.

Alcohol consumption is another of those situations where personal choice is always going to be an issue. According to the March of Dimes as little as one drink per week caused a smaller brain circumference in newborn infants. Fetal Alcohol Syndrome is associated with heavy users of alcohol, but Fetal Alcohol Affect is associated with more minimal use of alcohol.

"We must prevent all injury and illness that is preventable in society, and alcohol-related birth defects are completely preventable," Dr. Carmona said. "We do not know what, if any, amount of alcohol is safe. But we do know that the risk of a baby being born with any of the fetal alcohol spectrum disorders increases with the amount of alcohol a pregnant woman drinks, as does the likely severity of the condition. And when a pregnant woman drinks alcohol, so does her baby. Therefore, it's in the child's best interest for a pregnant woman to simply not drink alcohol." (http://www.surgeongeneral.gov/pressreleases/sg02222005.html)

I will encourage you to be supportive of this pregnant person and try to avoid nagging. Pregnancy does not last forever, and maybe if this person is aware of the facts associated with her substance use, she will make the quality decision to avoid using for the duration of her pregnancy.  If this person's alcohol use is "out of control" an intervention might be useful.  As a last resort, you might consider a referral to the department of children's protective services, but, only as a last resort.