How does a baby know when it is time to be born? Carole Mendelson, an obstetrician-gynecologist and biochemist at the University of Texas Southwestern Medical Center, may have finally found the mechanism that induces labor, a discovery that could help prevent some of the half million early births that occur every year in the United States. Mendelson made the finding while studying lung surfactant, a mixture of fats and proteins that helps the lungs expand and contract. As a fetus matures, it produces more of these compounds. One of the last to peak, she noticed, is the protein SPA-1, which shows up in large concentrations only a day or so before labor begins. To determine if there is a correlation, she injected SPA-1 into the amniotic sacs of 17 pregnant mice. Fourteen of them delivered prematurely. When Mendelson treated 15 pregnant mice with antibodies that blocked the action of SPA-1, they gave birth at least 24 hours late. “Mice have a gestation period of only 19 days,” she says, “so we’re talking about a significant time difference.”
Those results show that it could be possible to block premature birth. SPA-1 is not just a surfactant, Mendelson notes; it also stimulates inflammation of the uterus. Fetus-triggered uterine inflammation is known to initiate normal labor, but any infection that inflames the uterus can cause babies to be born too soon. Both responses seem to be controlled by SPA-1. “If we know the signal, we may be able to intercept it,” Mendelson says, fighting the infection while keeping the uterus from swelling until the fetus is ready to enter the world.