When you are pg, your body releases a hormone called relaxin that is designed to alow your pelvis to spread to accommodate a growing baby and also to allow it to pass through when giving birth. There is a gap at the front of your pelvis and this is what spreads apart during birth and during the later stages of pg, you can fit a finger width in the gap if you push down on your pubic area. Some women have trouble though with the relaxin working too well and can have joint stability problems.