What is the Pelvic Floor?
The pelvic floor is a sling of muscles, ligaments and sheet-like tissues that forms the base to your pelvis. It stretches from your front public bone to the back of your spine and creates the base support for your whole core cylinder.
The pelvic floor is fairly reactive; it can stretch in response to weight, it supports your bladder, bowel, and uterus (womb), and is designed to bear the weight of pregnancy. It gives you control when you empty your bladder and bowels, which is very handy in the later stages of pregnancy.
It also plays a role in hip and core stability by engaging with or helping other muscles of your core react.
Thought like any muscle, the muscles or tissues can become overstretched and weak if they are not exercised.
http://paternosterpilates.com/pregnancy-and-the-pelvic-floor/