Pregnant women who use cocaine or heroin while taking methadone to beat their addiction may weaken their placenta, opening the door to dangerous infections that could further harm an unborn baby, researchers said on Thursday.

A pregnant woman is seen in a file photo. 
REUTERS/Mykhailo Markiv
Their study in a laboratory found that exposure to either of the drugs in the presence of methadone -- used to wean people off narcotics -- harmed the placenta and allowed other dangerous substances through the organ's protective barrier.

As the consumption of illegal drugs, especially cocaine, is increasing in many countries, our results ... may improve the practical management in monitoring pregnant women, Antoine Malek of Zurich University Hospital and colleagues reported.

More toxic substances or bacteria and viruses may cross the placenta and harm the fetus.

The placenta is an organ rich in blood vessels that develops in the lower part of the womb during pregnancy. It transfers oxygen and nutrients from the mother to the fetus and is expelled after birth.

The researchers collected placentas from uncomplicated pregnancies after caesarean section from a group of volunteers. Experiments showed that while the drugs did not increase the transfer of methadone, they did allow other toxic substances or bacteria to seep through.

The findings, published in BioMed Central's Reproductive Biology and Endocrinology, suggest this somehow compromises the protective barrier function of the placenta, the researchers said.