Balancing act: excess steroids during pregnancy may pose risks for offspring.

A baby born prematurely risks having underdeveloped lungs that leave the newborn vulnerable to serious health problems. For that reason, a pregnant woman who shows signs of delivering very early often receives steroid hormones, which speed her fetus' lung maturation. Physicians have debated the appropriate dose of the steroid medication.

Now, researchers working with monkeys report that large doses of one of the steroids often given to pregnant women can have deleterious effects on offspring.

The researchers gave 42 pregnant monkeys a small, medium, or large dose of the steroid drug dexamethasone in their chow during the second half of pregnancy. Sixteen other pregnant monkeys received no steroids.

Seven stillbirths occurred among the steroid-exposed monkeys, but there were no stillbirths in the unexposed group.

Although no birthweight differences showed up among the four groups, at ages 8 to 12 months, monkeys that had been exposed to the larger two doses of dexamethasone in the womb weighed less and had shorter leg bones than did the unexposed animals, the researchers report in the April Journal of Clinical Investigation.

Moreover, at 12 to 14 months, the monkeys receiving high or medium doses of the steroid had higher blood pressure and fewer--and smaller--insulin-producing cells in their pancreases than the control monkeys did.

The medium- and heavy-exposure monkeys also overproduced insulin when given sugar and had more fatty tissue--even though they weighed less overall--than the unexposed animals did.

"This does look like insulin resistance; says study coauthor Jonathan R. Seckl, an endocrinologist at the University of Edinburgh. Insulin resistance is a prediabetic condition in which cells fail to process glucose efficiently. The findings suggest that heavy steroid exposure in the womb can introduce physiological effects that persist long after birth, he says.

Obstetrician Alan M. Peaceman of Northwestern University's School of Medicine in Chicago notes that past studies of babies born at least 1.5 months premature have established that those getting the steroid drugs in utero "did significantly better than those who didn't get them." The hormones jump-start the production of a viscous substance that the lungs require to develop flexibility.

Peaceman acknowledges risks from steroid treatment during pregnancy, as rodent studies and clinical observations had suggested. In each patient, he says, "we are weighing the benefits versus the downside of steroid use."

Seckl agrees that steroids provide a benefit in many pregnancies. "The issue is, if some steroid is good, more is not necessarily better," he says.

In past decades, obstetricians sometimes gave multiple courses of steroids rather than a single course of two doses 24 hours apart, as now recommended by the National Institutes of Health. Doctors had thought that steroids' salutary effect on the fetus wore off after a week or so, Peaceman says. But he notes that recent findings suggest that a single course of steroids carries benefits longer than that.