If a woman is confined to bed rest during pregnancy, there is a likelihood of significant bone loss, the results of a new study indicate.

Dr. Joanne H. E. Promislow, of the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, and colleagues measured bone mineral density at approximately 16 and 36 weeks of pregnancy in 181 women receiving prenatal care.

The researchers found that, overall, bone loss averaged between 0.4 percent and 1.9 percent during the 20-week period, depending on where the measurements were taken.

A total of 34 women (19 percent) experienced bone loss exceeding 5 percent, the team reports in the American Journal of Obstetrics and Gynecology.

On average, women who were prescribed bed rest had average losses of 4.6 percent, compared to 1.5 percent among women who did not go on bed rest. Women who were prescribed bed rest were 6.5 times more likely to experience bone loss of 5 percent or more during the 20-week period.

“These strong findings generate the need for additional study with more detailed information on bed rest duration and compliance, and on recovery of bone mass after pregnancy,” the investigators conclude.

In fact, they suggest that the benefits of bed rest for specific pregnancy complications should be looked at more closely, because of the “the potential for harm.”

SOURCE: American Journal of Obstetrics and Gynecology, October 2004.