Towards the end of your pregnancy you will notice that your bump is sometimes very hard. The uterus is a muscle. At the end of pregnancy that muscle is completely stretched. That muscle responds to any stimulus, such as lifting heavy shopping bags out of the car, a full bladder, running after your toddler. A muscle that is stimulated pulls together. This is a tightened belly, not labor. The fibers of the uterine muscle are not working together.
During a contraction your uterus pulls together too, but in a different way. The muscle fibers work together then. Contractions move in a wave-like motion from the top of the uterus to the bottom. Some women describe contractions as strong menstrual cramp. It comes, rises to a peak and ebbs away again. During a contraction your baby is pushed deeper into your pelvis, the head presses the cervix, causing dilatation.
Contractions are effective when labor progresses with 1 cm per hour or more. This can only be checked with a vaginal examination.
No matter how painful, how long, how hard you need to work coping, contractions are only effective contractions when they lead to adequate progress of labor. Nothing is more frustrating than painful contractions (that perhaps some professional will call ‘good contractions’ because they are long and painful) for nothing. You are breathing like you were taught, your husband is rubbing your back, only to find out that labor is not progressing. Cooperation between the muscle fibers is not good. This happens especially in women who give birth for the first time.
When labor is not progressing sufficiently, even if you are still under 3-4 cm, corrective interventions like rupturing your membranes or augmentation with oxytocin are advised.