The effect of parity on uterine activity in labour.

Uterine activity was studied in 40 multiparous Singapore women of Chinese origin who were in normal labour and had a normal delivery. A catheter tip pressure transducer coupled with a uterine activity integrator was used to quantify uterine activity. Normal labour progress was defined as labour progressing within 2 h to the right of a line drawn on the partogram at 1 cm/h in the active phase of labour. A wide range of activity was observed. The median level of uterine activity rose from 815 kPas/15 min at 3 cm dilatation to 1731 kPas/15 min at 9 cm dilatation with an overall median level of 1130 kPas/15 min. The 10th centile value rose from 430 kPas/15 min at 3 cm dilatation to 923 kPas/15 min at 9 cm dilatation. Profiles of dilatation-specific activity values were constructed. These values were significantly lower than in a comparative group of nulliparous patients. The parous uterus requires to expend significantly less effort to effect normal vaginal delivery than its nulliparous counterpart.