During pregnancy, uterine contractility is tightly regulated to prevent premature labor. In the early stages, progesterone maintains uterine quiescence. As pregnancy progresses, the uterus undergoes Braxton Hicks contractions, which are irregular and usually painless. These "practice contractions" prepare the uterus for labor. During labor, oxytocin and prostaglandins increase, leading to strong, regular contractions that facilitate childbirth.
