Your support is essential in dealing with this unhealthy behavior. You understand the dangers of substances to the unborn child and mother. Examine the mother's history and experiences with substances. Enlist the help of a doctor by going with her to her monthly check ups. Enlist the help of her family and friends. If addiction is the problem, help her seek counseling to quit or remain abstinent during pregnancy. Try not to be judgemental, but encourage her by your concern for her health as well as the unborn child. The dangers of these behaviors are well documented as seen in the link below, and the foundation March of Dimes that promote healthy behaviors for pregnant women. I commend your interest in this topic of concern for healthy babies!
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.
If you know them you should try to convince them about the harm it could bring about to the baby. Smoking and drinking during pregnancy is very dangerous not only to the mother but also to the baby as well since the baby is actually connected to the mother in the womb. If you know her well it would be best to warn her about the damage she can do to her baby
Mapriem's answer is excellent.
But remember, there is a little over-exaggeration about this subject. I remember a friend of mine who smoked about four cigs a week while pregnant and people were fussing and panicing and telling her she was 'killing her baby' etc and making her life a misery. But she wanted to smoke 20 a day and was doing very very well! Nobody was supporting her, only being negative! The occasional cigarette or the occasional drink is not going to harm the foetus.
On the other hand, large quantities of cigarettes, alcohol or any other drug are a serious threat to the unborn child's and the mum needs firm help and support - not criticism and nagging.