Basically, marijuana's active ingredient, tetrahdyrocannabinol (THC), may interfere with the development of nerve cells, according to the researchers.
They included Tibor Harkany, PhD, who works in Stockholm, Sweden, at the Karolinska Institute's molecular neurobiology division.
Harkany's team studied mice and cell cultures from frogs.
According to the National Institute on Drug Abuse (NIDA), previous research has shown that some children born to women who abused marijuana during pregnancy may show signs of neurological problems in development and problems with memory and attention.
Harkany and colleagues studied a certain type of receptor in the brain. Those receptors latch onto chemicals called endocannabinoids.
The researchers explain that in a fetus, those receptors guide the development of axons, which are the long fibers of nerve cells. As the fetal brain develops, axons position themselves so they can communicate with each other.
But that process goes awry in mice with genes for impaired cannabinoid receptors. Those mice's axons didn't position themselves properly in Harkany's study. That could create communication problems between axons.
THC may mimic those effects in the fetal brain when used during pregnancy, note Harkany and colleagues. However, they didn't directly test that theory.
The study appears in the journal Science.