What causes labor to begin?

Researchers believe that the most important trigger of labor is a surge of hormones released by the fetus. In response to this hormone surge, the muscles in the mother’s uterus change to allow her cervix (at the lower end of her uterus) to open.

In other words, when a woman goes into labor on her own, it’s a powerful signal that her baby is ready to be born and that her body is ready for labor.