Fetus May Signal to Start Birth Process

A developing fetus may signal when it is ready to be born by releasing a chemical produced by the lungs, according to a new study by U.S. researchers.

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.

Writing in the Proceedings of the National Academy of Sciences, Dr. Carole Mendelson of the University of Texas Southwestern Medical Center at Dallas 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 preterm 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 preterm labor,” Mendelson said.

Mendelson said understanding more about this process may help lead to the development of therapies that could prevent preterm labor.

In mice, the developing fetal lung starts producing SP-A at 17 days gestation and mouse pups are born at 19 days. The developing human fetus starts producing excess SP-A at 30 to 32 weeks in a normal 40-week gestation.

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, whereas blocking it delayed delivery.