Enlargement of the opening of a tubular structure. This usually refers to the cervical dilation that occurs during labor. The opeining of the cervix must go from essentially 0 centimeters to about 10 centimeters, the usual size required for the baby to pass through the cervix, which forms part of the birth canal. The first stage of labor is that part of labor during which the cervix dilates up to 10 cm or is completely dilated. This usually takes several hours and is shorter with subsequent pregnancies.
BabyZone: Labor and Delivery