Many substances including alcohol, nicotine, and other drugs of abuse can have negative effects on the developing fetus because they are transferred to the fetus across the placenta. For example, nicotine has been connected with premature birth and low birth weight as has the use of cocaine. Heroin exposure results in dependence in the newborn, requiring treatment for withdrawal symptoms. It is often difficult to tease apart the confluence of factors that go with drug abuse during pregnancy—poor nutrition, inadequate prenatal care, stress, and psychiatric comorbidities—all of which may impact fetal development.