The likelihood of a good outcome of fertility treatment is reduced if either the man or the woman uses marijuana, compared with couples that don’t use it, the results of a new study suggest.

If these study findings are confirmed by additional research, we would recommend that physicians tell couples to not use marijuana for at least one year before starting fertility treatment, Dr. Hillary S. Klonoff-Cohen from University of California, La Jolla, told Reuters Health.

Klonoff-Cohen and colleagues investigated the possible effects of marijuana use on the outcomes of 221 couples who underwent in vitro fertilization (IVF) or gamete intrafallopian transfer (GIFT) treatment for infertility. The findings are published in the American Journal of Obstetrics and Gynecology.

At least 10 percent of men and women smoked marijuana in the year before the fertility procedure, the authors report, and 3 percent of women and 0.5 percent of men reported smoking marijuana the day before the procedure.

Longer marijuana use over a woman’s lifetime reduced the number of eggs that could be retrieved and the number of embryos that could be transferred, the results indicate.

Women who smoked marijuana during the year before the procedure had 25 percent fewer eggs and about one fewer embryo transferred, compared with women who didn’t smoke marijuana during that year, the researchers note.

Similarly, marijuana smoking by the man during the year before the procedure was associated with approximately one fewer embryo transferred, the report indicates.

Any lifetime use of marijuana by both partners was associated with a 19 percent decrease in eggs retrieved, compared with couples who never smoked marijuana.

Furthermore, Klonoff-Cohen’s group found that if the man or the woman had ever used marijuana, their infant had a significantly lower birthweight, compared with individuals who had never used marijuana. This effect seemed to increase with higher or more recent marijuana use.

“Marijuana has been implicated with low birthweight, although the results are inconsistent,” Klonoff-Cohen commented. However, this is the first report of a relationship between marijuana use by the father and low infant birth weight, so our findings need to be verified by larger studies.

“We are currently evaluating the effect of marijuana use on intracytoplasmic sperm injection patients,” Klonoff-Cohen added.

SOURCE: American Journal of Obstetrics and Gynecology, February 2006.