And then we have stage three, which lasts about ten to 15 minutes. So let's begin with stage one. So in stage one is when special hormones are released by the body and they stimulate the contraction of the walls of that uterus. Remember, the wall of the uterus not only has that endometrium, but it also contains smooth muscle. And that smooth muscle is capable of contracting. And so in the first stage of the birthing process, also known as labor, this is when the contraction of that uterus begins.