This change typically occurs at night, suggesting neural control, and significantly increases intrauterine pressure. Some women may experience contractions before labour is due. These are Braxton Hicks contractions, which are sometimes referred to as "false labour." There are several endogenous compounds involved in coordinating uterine contractility in labour, including oxytocin and prostaglandins. Oxytocin
The hormone oxytocin has been identified as inducing uterine contractions, and labour in general. Oxytocin is produced by the body naturally and since the 1950s has also been available in synthetic pharmaceutical form. In either form, oxytocin stimulates uterine contractions to accelerate the process of childbirth. Production and secretion of oxytocin is controlled by a positive feedback mechanism, where its initial release, either naturally or in pharmaceutical form, stimulates production and release of further oxytocin. For example, when oxytocin is released during a contraction of the uterus at the start of childbirth, this stimulates production and release of more oxytocin and an increase in the duration, intensity and frequency of contractions. This process compounds in intensity and frequency and continues until the triggering activity ceases. Prostaglandins
The concentration of prostaglandins in the blood plasma and amniotic fluid increases during labor. These inflammatory mediators encourage myometrial contractions to induce labor. Prostaglandins are also related to the changes in gap junction formation and connexin-43 expression during labor. In orgasm
Uterine and vaginal contractions usually take place during female sexual stimulation, including sexual arousal, and orgasm.
Monitors
Uterine contractions can be monitored by cardiotocography, in which a device is affixed to the skin of the mother or directly to the fetal scalp. The pressure required to flatten a section of the uterine wall correlates with the internal pressure, thereby providing an estimate of it.A type of monitoring technology under development at Drexel University embeds conductive threads in the knitted fabric of a bellyband. When the fibers stretch in response to a contraction, the threads function like an antenna, and send the signals they pick up to an embedded RFID (radio-frequency identification device) chip that reports the data. Mechanism
Resting state
The resting membrane potential (Vrest) of uterine smooth muscle has been recorded to be between −35 and −80 mV. As with the resting membrane potential of other cell types, it is maintained by a Na+/K+ pump that causes a higher concentration of Na+ ions in the extracellular space than in the intracellular space, and a higher concentration of K+ ions in the intracellular space than in the extracellular space. Subsequently, having K+ channels open to a higher degree than Na+ channels results in an overall efflux of positive ions, resulting in a negative potential. This resting potential undergoes rhythmic oscillations, which have been termed slow waves, and reflect intrinsic activity of slow wave potentials. These slow waves are caused by changes in the distribution of Ca2+, Na+, K+ and Cl− ions between the intracellular and extracellular spaces, which, in turn, reflects the permeability of the plasma membrane to each of those ions.