May 6 (HealthDay News) -- Researchers report they have identified a marker that might predict which pregnant women will pass meconium during delivery.

Meconium is essentially a baby's first bowel movement, excreted in the womb, and often expelled with the amniotic fluid. It is considered a sign of fetal distress. A small percentage of newborns inhale a mixture of meconium and amniotic fluid, which can lead to serious lung injury or infection.

"Meconium in and of itself is not necessarily a bad thing," Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City, explained. "It's a bad thing when you have meconium complications like aspiration. It's like being born with the umbilical cord around the neck. Twenty-five percent of babies are born this way, but for most of them, it's not a big deal. It's the same thing for meconium. Only a small number of [babies born with] meconium-stained fluid actually aspirate."

In fact, 11 percent of babies aspirate meconium-stained fluid, but the situation is not dire in all cases.

It's unclear how this latest finding will actually help physicians and expectant mothers during delivery.

"At this point, I don't know what we're going to do with this data," said Wu. "It's not like you would do anything differently or perform a C-section. We need additional studies in order to find a clinical intervention that can help."

The findings were expected to be presented Tuesday at the American College of Obstetricians and Gynecologists annual meeting, in New Orleans.

For this study, researchers from Lincoln Medical Center in the Bronx, N.Y., drew blood to measure levels of a hormone, inhibin-A, in 19 pregnant women who had had a normal pregnancy and delivery.

Inhibin-A levels were higher in four women who had normal pregnancies but who passed meconium during delivery. The test was conducted during the second trimester.

SOURCES: Jennifer Wu, M.D., obstetrician/gynecologist, Lenox Hill Hospital, New York City; May 5, 2008, presentation, American College of Obstetricians and Gynecologists annual meeting, New Orleans