Cocaine, like nicotine, tends to constrict blood vessels, sometimes with dire consequences. Constriction of blood vessels is thought to be responsible for certain fetal abnormalities associated with cocaine abuse including failure to form part of the intestines and failure to form the limbs properly. Congenital heart defects and urinary tract abnormalities have also been observed. The effects on the fetus' central nervous system varies from major disruptive brain anomalies to the disordered behaviors seen in newborns. Newborns tend to have depressed interactive behavior and have difficulty organizing their responses to the outside world.
Research is currently underway to study the long-term effects of cocaine use during pregnancy.
Opiates Heroin and methadone are the most frequently encountered drugs in this class used during pregnancy. Although neither causes congenital abnormalities, they pose a significant threat not only because use of heroin involves needles and thus may increase the risk for HIV infection but also because withdrawal can be fatal to the fetus. Also, there is an increased incidence of inflammation and infection of the placenta and the uterus. Opiate use is also associated with an increased risk of premature labor and delivery, low birth weight, fetal distress, and neonatal infections. The addicted babies will undergo the Neonatal Withdrawal Syndrome.