Contractions start in the muscles of the uterus, specifically at the top of the uterus, and then move downward. This wave-like tightening begins at the upper part of the uterus and spreads down through the abdomen

. During a contraction, the uterus tightens and the abdomen becomes hard, then relaxes and softens as the contraction ends

. These contractions help to dilate (open) the cervix and move the baby down the birth canal during labor

. Early in pregnancy, contractions may occur but are usually not felt; they become stronger, more regular, and more painful as labor progresses

. Braxton Hicks contractions, which are practice contractions, also start similarly but are generally painless and irregular, often felt as a tightening that starts at the top of the bump and spreads downward

. In summary, contractions begin at the top of the uterus and move downward through the abdomen as the uterus tightens and relaxes during labor