Braxton Hicks contractions
These actually start very early on, and you will have them even during the late first trimester of pregnancy. You will not notice them immediately because your uterus will still be tucked into your abdominal cave in the early stages of pregnancy, but they will become clear to you soon enough. At first, Braxton Hicks contractions will present as a hard feeling inside your abdomen. When you touch your belly, it will feel like stone. Some women have Braxton Hicks contractions that hurt a little during the later months of pregnancy.
During early labor, you might experience a light tightening inside your uterus that passes so quickly you wonder whether you really felt that. They get stronger and a pattern becomes clear later on, when your contractions will also last longer. Some people describe labor contractions as "surges", and this is pretty appropriate because a contraction starts lightly, peaks, and wears off again. You know how you wring out a wet towel or a t-shirt you washed by hand?
Imagine what those fabrics would feel like if they could perceive, and you'll just about have the feeling of a labor contraction. Some types of contractions are felt strictly inside the uterus, at the front of your belly. Other women have "back labor" and will feel pain in their back and hips as they are going through a contraction. Levels of pain will vary, but it is fair to say that almost every woman experiences some level of pain while she is in labor.