A developing fetus may signal when it is ready to be born by releasing a chemical produced by the lungs, U.S. researchers said Monday.
The study, done in mice, suggests that in mammals, readiness to breathe outside the mother’s womb might be the main factor in determining when it is time to be born.
“We found that a protein within lung surfactant serves as a hormone of labor that signals to the mother’s uterus when the fetal lungs are sufficiently mature to withstand the critical transition to air breathing,” said Dr. Carole Mendelson, a professor of biochemistry and obstetrics and gynecology at the University of Texas Southwestern Medical Center at Dallas.
“No one really understands what causes normal or pre-term labor. There may be several chemical pathways that lead to labor, but we think that this surfactant protein, which is also produced by the fetal lung in humans, may be the first hormonal signal for labor,” added Mendelson, who led the study.
Writing in the Proceedings of the National Academy of Sciences, Mendelson and colleagues said they looked at surfactant protein A, which is essential for normal breathing outside the womb.
In humans surfactant protein A, or SP-A, also helps immune cells called macrophages attack invaders such as bacteria, viruses and fungi in the lungs.
“Women who go into prettier labor frequently have an infection of the membranes that surround the fetus, and the number of macrophages in the wall of the uterus increases with the initiation of prettier labor,” Mendelson said.
Infection, pre-term labor linked?
So there must be a connection between infection and prettier labor. Mendelson said understanding more about this process may help lead to the development of therapies that could prevent prettier labor.
In mice, the developing fetal lung starts producing SP-A at 17 days gestation and mice pups are born at 19 days. The developing human fetus starts producing more SP-A at 30 to 32 weeks in a 40-week normal gestation.
As the fetus “breathes” amniotic fluid in the womb, SP-A is released into the fluid.
Macrophages activated by the protein make their way through the amniotic fluid to the wall of the uterus. Once embedded there, they produce a chemical that stimulates an inflammatory response in the uterus, ultimately leading to labor.
The researchers found that injecting a pregnant mouse with SP-A before day 17 of the pregnancy caused the mouse to deliver early, and blocking it delayed delivery.
