Uterine contractions are part of the natural delivery process (i.e. not by caesarean section). It has been found that the hormone oxytocin induces uterine contractions and works in general. Oxytocin is produced naturally by the body and has also been available in synthetic dosage form since the 1950s.   In both forms, oxytocin stimulates uterine contractions to speed up the birth process. The production and secretion of oxytocin is controlled by a positive feedback mechanism, in which its initial release, naturally or in dosage form, stimulates the production and release of additional oxytocin. For example, when oxytocin is released during a contraction of the uterus at the beginning of childbirth, it stimulates the production and release of more oxytocin and an increase in the duration, intensity and frequency of contractions. This process multiplies in intensity and frequency and continues until the triggering activity ceases. Understanding the normal contraction pattern is also useful for defining work stoppage, which has a different management depending on the stage. For example, a stopped latent phase is an indication for the increase with oxytocin, while a stopped active phase is an indication for caesarean section.
The definition of true work stoppage requires an analysis of the adequacy of uterine contractions, which requires the use of an intrauterine pressure catheter. Active phase shutdown has specific requirements that include four or more hours of appropriate contractions or six or more hours of insufficient contractions. These definitions are essential for clinicians because they dictate management algorithms. CST, developed by Ray and Freeman8 in the early 1970s, measures fetal response to maternal contractions. Late slowdowns after contraction may indicate fetal hypoxia as a result of uteroplacental insufficiency. Childbirth involves redesigning the ECM of the cervical wall so that it softens and expands in response to the ascending circumferential force of myometric contractions, increased intrauterine pressure, and gravity. Changes in the biomechanical properties of the cervix begin before the onset of active labor and can be divided into three phases: softening, maturation and dilation. Softening of the cervix occurs by restructuring the architecture of collagen and gradually increases after the middle of pregnancy, which leads to a gradual thinning of the cervical wall and shortening of the cervical canal (that is, the distance between the uterus and the vaginal openings). Although the tensile strength of the cervix is maintained during the softening phase, the rate of softening and decrease in cervical length, which can be monitored by ultrasound, can affect the time of birth, as cervical shortening in the middle of pregnancy is a powerful predictor of preterm birth.
In contrast, cervical dilation occurs at birth and within a few hours during active labor. This dramatic biomechanical change significantly reduces the ability of the cervix to resist traction and, as a result, the cervical canal expands in response to labor contractions and simultaneous downward pressure from the fetus (usually the fetal head). Finally, dilation becomes sufficient to allow myometric contractions to force the conceptus into the vaginal canal and subsequent delivery. After birth, the cervix is reconstructed to restore the rigid ECM architecture and narrow canal. Uterine contractions that occur throughout the menstrual cycle, also known as endometrial waves or contractile waves, seem to affect only the subendomeric layer of the myometrium.  If implantation does not take place, the frequency of contractions remains low; but with menstruation, the intensity increases significantly between 50 and 200 mmHg, creating labor-like contractions.  These contractions are sometimes called menstrual cramps, although this term is also used for menstrual pain in general. These contractions can be uncomfortable or even painful, but they are usually much less painful than contractions during labor. Painful contractions are called dysmenorrhea. Progesterone: It decreases permeability to calcium, sodium and potassium and modulates intracellular binding to calcium, making less calcium available to the calmodulin-MLCK system by increasing the rate of cAMP synthesis.
It is important for the maintenance of pregnancy, since it causes uterine relaxation in early pregnancy, and its functional withdrawal leads to an increase in the estrogen-progesterone ratio, which causes an increase in the concentration of prostaglandins that triggers labor.  A CST is positive if more than 50% of contractions are followed by a late slowdown. Overstimulation of the uterus, defined as contractions that occur more often than every 2 minutes or last more than 90 seconds, should not be present. Ambiguous CST occurs when overstimulation is stopped or when occasional late slowdowns are detected. A negative CST is a CST where no slowdown is detected. Strong uterine contractions compress the uterine blood vessels and prevent continuous bleeding at birth. There is evidence, albeit from animal models, that the fetus may contribute to changes in uterine activity by (1) affecting its influence on placental asteroid hormone production, (2) mechanical stretching of the uterus, and (3) secretion of neuropituitary hormones and other stimulators of prostaglandin synthesis. It is believed that the last common pathway for labor is the activation of the fetal hypothalamic-pituitary-adrenal axis.
What is interesting, however, is the observation that spontaneous labor occurs in women, even if a fetus is anencephaly (without a functional pituitary gland), suggesting that intact neuropituitary function is not a prerequisite for the onset of human labor.77 Contractions are usually evident. They are usually easy to distinguish from fibroids because fibroids are usually more inhomogeneous and often deform the outer uterine contour. However, since contractions may rarely be inhomogeneous and the outer uterine contour rarely swells, it may be necessary to observe a change over time to prove that the area is a contraction (see Fig. 20-22B, 20-23B and 20-24B). Contractions last a variable period of time, rarely more than 1 hour, and a repeated study within 30 minutes often shows a sufficient change to confirm the diagnosis. If a contraction continues, a longer time interval, even a study on another day, may rarely be necessary. Does the pelvis seem sufficient for the infant? A delay in the active phase indicates either an insufficient effort of contraction of the uterus to enlarge the cervix, or a mechanical obstruction of childbirth. Obviously, this is a critical issue, because therapeutic alternatives are very different. If the pelvis is clinically small and/or the fetus is large and labor appears severe (e.B.
intense uterine contractions that occur every 2 minutes), the choice is caesarean section. .