Researchers have shown that pre-natal exposure to cocaine and heroin increases the permeability of the placenta, increasing the passage of some chemicals into the fetus. Antoine Malek led a team of researchers from Zurich University Hospital’s Department of Obstetrics, who used a perfusion technique to study human placental tissue function in the lab.

They found that exposure to cocaine and/or heroin in the presence of methadone increased transfer of a test chemical called antipyrine across the organ. “As the consumption of illegal drugs, especially cocaine, is increasing in many countries, our results concerning cocaine and heroin causing an increased antipyrine transfer may improve the practical management in monitoring pregnant women,” said Malek.

As many people addicted to drugs find it extremely difficult to abstain from drugs when they become pregnant, maintenance treatment with methadone is often used to limit damage to the developing fetus. But methadone itself can also be dangerous, and too much fetal exposure to it can lead to harmful withdrawal symptoms in the newborn.

Malek and his colleagues sought to investigate the effects cocaine and heroin on the placenta. They found that while the narcotics didn't increase transfer of methadone, they did allow transfer of other test substances, which suggests that the barrier function of the placenta may be compromised when cocaine or heroin are present.

"More toxic substances or bacteria and viruses may cross the placenta and harm the fetus. Previous studies have reported increased prevalence of infectious diagnoses in cocaine-exposed infants,” said Malek.

These results emphasize the fact that pregnant drug users who can't abstain completely must attempt to exclusively use methadone. Combining it with other drugs could cause extra harm to their child.