Characteristics of uterine activity in nulliparous labour.

Uterine activity was studied in 40 nulliparous Chinese women who were in normal labour and had a normal delivery. A catheter-tip pressure transducer coupled with a uterine activity integrator was used to observe and quantify uterine activity. Normal labour progress was defined as labour progressing within 2 h to the right of a line drawn at 1 cm/h in the active phase. A wide range of uterine activity was recorded with varying degrees of co-ordination. The minimum level of uterine activity likely to be associated with labour progress was 650 kPas/15 min at 3 cm cervical dilatation. The median level in the active phase of normal labour was 1440 kPas/15 min. There was a strong correlation between measurements in kPas/15 min and Montevideo units/15 min (r = 0.71, P less than 0.001). No significant increase was found in basal tone.