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2 Aug, (foodconsumer.org) - Women who use marijuana at the time of conception or very early in pregnancy face an increased risk of miscarriage or ectopic pregnancy, a new study suggests.

Marijuana’s active ingredient called tetrahydrocannabinol (THC) interferes with the body signaling system and prevents the implantation of the fertilized egg in the womb, the study said.

University of Nashville researchers warned that smoking marijuana at a delicate time immediately before or after conception might lead to miscarriages or ectopic pregnancies. The cannabinoid receptors, CB1 and CB2 are located in the brain and are also present in sperm, eggs, and newly formed embryos.

When the psychoactive ingredient of marijuana, tetrahydrocannabinol (THC), binds to these receptors a chain of events is set into motion. This culminates in the "high" experienced by smoking pot. During early pregnancy a molecule called anandamide, which occurs naturally, activates CB1 and CB2.

Anandamide is vital for normal embryonic development. It is synthesized by an enzyme called NAPE-PLD and is broken down by another enzyme called FAAH.

The current study led by Professor Sudhansu Dey of Vanderbilt University in Nashville, Tennessee, found that the production and breakdown of anandamide is a sensitive process and any alteration could lead to complications like preventing normal embryo development, transport into the womb and implantation.

The researchers studied the effect of THC in mice and found that affects the body in much the same way as high levels of anandamide. The signaling process goes haywire and thus prevents the embryo from being implanted in the womb.

In mice the researchers suppressed the activity of FAAH enzyme. This meant that high levels of anandamide accumulated in the body. These high levels of anandamide prevent the embryos from completing their passage to the uterus, thus compromising the pregnancy.

"Marijuana exposure may compromise pregnancy outcome," said Dey, the corresponding author of the study, published in the August issue of the Journal of Clinical Investigation.

"This is a major finding, that if you block FAAH and disturb anandamide levels, there is a compromised pregnancy outcome. This occurs very early during pregnancy, right from the start of fertilization. This may explain tubal pregnancies, it may be one cause of retention of embryos in the oviduct."

Dey said that all embryos in mice that were administered THC failed to reach the womb. "Our present findings have high clinical importance, since embryo retention in the fallopian tube is a significant cause of ectopic pregnancy in women, the incidence of which has markedly increased during the past decade," he added.

"I think the effect should not be permanent but smoking marijuana means the THC level might go up and interfere with early pregnancy, even before fertilization."

In an accompanying commentary in the same journal, Herbert Schuel from the State University of New York, said the study was thought provoking since many of the drugs currently in development or in use to suppress appetite or trigger weight-loss are known to have similar effects like THC on anandamide signaling.

Such drugs needed to be used with caution, he said. The present study "provides insight into normal mechanisms that regulate early development of the embryo and its transport through the oviduct to the uterus," he added.

Marijuana or pot is not freely available in the US, but it is still one of the most widely abused illicit drugs in the world, and often by pregnant women. Most drugs have some adverse effect on pregnancy, but marijuana tops that list.

Previous studies have suggested that pregnant women who smoke pot can pass on memory problems including attention deficiency to their offspring. Additionally, March of Dimes says that using marijuana in pregnancy is linked to low birth weight and to symptoms in the baby, such as excessive crying and shaking.

The conclusion reached by the study is that pregnant women are better off staying away from smoking pot. If you are already pregnant, there is no evidence that marijuana smoking in the past will harm your baby, but like many other factors, this is again unpredictable.

Ectopic pregnancies occur when the fertilized egg fails to reach the womb. There are many causes for this condition and marijuana is not the only one. However the fact that the drug is involved in this process means that the risk of ectopic pregnancy is enhanced.

Dey put it very aptly when he said that the effect of THC on fertilized egg "raises concern that the adverse effects of maternal use of marijuana could be seeded very early in pregnancy."

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