Q. I have been running about 15 miles a week for the last two years and have just learned that I'm pregnant. Can I continue running or should I switch to some other form of exercise or stop exercising altogether? A. Pregnant women generally have been excluded from research studies because of concerns about the health of the fetus. Therefore, little research has been done on the effects, pro or con, of exercise during pregnancy. However, as Americans are becoming more involved in physical fitness, more women are continuing to exercise throughout their pregnancy, intuitively believing that it is beneficial. I think physicians, in trying to keep up with social changes, are reexamining previously held notions about exercise and work during pregnancy.

Anecdotal reports have been published about female athletes and long-distance runners continuing to train throughout pregnancy with few or no complications. However, there is evidence from animal and some human studies suggesting that strenuous exercise may be associated with slightly reduced birth weight, up to half a pound.

Until more is learned about the effects of exercise during pregnancy, the most prudent advice is to exercise to your previous level of tolerance. New, strenuous forms of exercise should probably not be first taken up during pregnancy.