Some time towards the middle of your pregnancy or even earlier, you may notice the muscles of your uterus tightening. If you place your hands on your bare bump when this is happening you can feel how hard your uterus becomes.
Each tightening usually lasts for about half a minute and usually does not cause you any discomfort. You may have this sensation once or twice an hour perhaps a few times a day.They get their name from John Braxton Hicks the English doctor who first described them in 1872.