Instrumented uterus and corresponding EMG and IUP correlation. Top: Chronically instrumented uterus of a pregnant cynomolgus monkey in situ at GD 120, showing two bio-potential electrodes attached to the myometrium for measurement of electromyograms (EMG, scale: electrodes are 1 cm apart) . A tube was inserted into the amniotic cavity for registration of the respective intrauterine pressure (IUP). Bottom: Correlation between uterine EMG (blue) and IUP (red). Typical bursts and corresponding contractions occur every 3–6 min. The highest spontaneous activity was observed in the night close to birth. Note the close relationship between bursts of electrical activity in the EMG and increases in IUP, here in the presence of OT infusion.