Uterine tachysystole

Uterine tachysystole is a condition of excessively frequent uterine contractions during pregnancy.

Because contraction counts are often measured over periods of ten minutes but averaged over periods of thirty minutes, there can be slight differences in how the cutoff is calculated. Generally it is defined as more frequently than once every two minutes. Although definitions may vary among studies, most use the terms defined by the American Congress of Obstetricians and Gynecologists (1999a) to describe increased uterine activity as follows:

• Uterine tachysystole is defined as 6 contractions in a 10-minute period.
• Uterine hypertonus is described as a single contraction lasting longer than 2 minutes.
• Uterine hyperstimulation is when either condition leads to a nonreassuring fetal heart rate pattern.

The American Congress of Obstetricians and Gynecologists amended these definitions in 2008. Uterine tachysystole is defined as 5 or more contractions in 10 minutes, averaged over a 30-minute period. The terms "hypertonus" and "hyperstimulation" are not recommended to be used.

Uterine tachysystole has been reported to follow vaginally administered Prostaglandin E2 in 1 to 5 percent of women (Brindley and Sokol, 1988; Rayburn, 1989). It can be associated with placental abruption and perhaps with uterine leiomyomas. It can also refer to hyperstimulation with oxytocin.