Uterine Hyperstimulation is a serious complication of labour induction. It is defined as as single contractions lasting 2 minutes or more, or five or more contractions in a 10 minute period. It can cause impairment to uteroplacental blood flow, and result in uterine rupture, placental abruption and fetal heart rate abnormalities.
Studies show that misoprostol can cause hyperstimulation, although the rate appears to be no different to when other cervical ripening drugs such as dinoprostone are used. For example, a study by Wing D et al. showed that there was a significant increase in the incidence of hyperstimulation in women administered a fixed dose of oral misoprostol compared to women administered oxytocin. This said, 7.5% of women administered fixed oral misoprostol experienced hyperstimulation, which is not abnormally high for women undergoing labour induction.
However, the hyperstimulation rate with titrated oral misoprostol may be lower than other induction agents. In a study by Ho M et al., titrated oral misoprostol was compared to oxytocin. There was no significant difference in prevalence of hyperstimulation between the two groups, and the incidence was greatly reduced compared to the previous study using fixed oral misoprostol.
This suggests that misoprostol can be a potential risk for hyperstimulation, but if it is administered in a titrated dose, the risk can be reduced greatly. This is, in part, the reason for the inclusion of oral misoprostol as one of the recommended induction agents in the 2011 WHO Induction of labour guidelines.