Reviewed on 3/09/2010
It is always best to avoid drug exposure during pregnancy, especially during the first three months, but having said that, I find very little evidence that smoking marijuana during pregnancy is as harmful to babies as smoking cigarettes or drinking alcohol. In fact, last year the British Journal of Obstetrics and Gynecology published results of a study involving more than 12,000 women that looked at the association between using marijuana before and during pregnancy and the outcome of pregnancy. The researchers found that five percent of the women reported smoking marijuana before or during their pregnancies. Those who continued to smoke marijuana at least once a week before and throughout pregnancy gave birth to babies whose birth weights were slightly lower than the other women's babies although the difference wasn't statistically significant. There were also no statistically significant differences in the birth-length and head circumference of the babies born to the women who smoked pot. Based on these observations, the researchers concluded that smoking pot during pregnancy wasn't associated with increased risks to the babies.
However, those findings may not tell the whole story. Earlier studies suggested that babies born to women who used marijuana during pregnancy display altered responses to visual stimulation, increased tremors, and a high pitched cry, which may indicate problems with nervous system development. During pre- and early school years, youngsters exposed to marijuana during pregnancy have been reported to have more behavioral problems and difficulties with sustained attention and memory than other children.
Researchers don't know if these effects disappear or persist as children grow. There is also a chance that other problems may come to light later since some parts of the brain continue to develop into adolescence. Bottom line: There is no hard evidence that marijuana is as dangerous as tobacco or alcohol when used during pregnancy, but it's always best to err on the side of caution.
Andrew Weil, M.D.