Antepartum ambulatory tocodynamometry: the significance of low-amplitude, high-frequency contractions.

The clinical significance of low-amplitude, high-frequency contractions was examined during pregnancy in 142 women who underwent daily ambulatory tocodynamometry between 23-36 weeks' gestation. The results indicate that patients destined to develop preterm labor had this contractility pattern significantly more often than did their counterparts who delivered at term (13.5 versus 9.2%; P less than .01). Parity and gestational age had no effect on the occurrence of low-amplitude, high-frequency contractility, but this pattern was also significantly more prevalent in the presence of multifetal gestations, independent of the occurrence of preterm labor. The institution of tocolytic therapy was accompanied by a 50% decrease in the proportion of time occupied by low-amplitude, high-frequency contractions. Although this contraction pattern occurred significantly more often among patients who later developed preterm labor, calculations of its predictive values, specificity, and sensitivity indicate that its presence has relatively limited clinical significance.