Risk of uterine rupture after the partographic 'alert' line is crossed--an additional dimension in the quest towards safe motherhood in labour following caesarean section.

To determine if prolonged active phase of labour is associated with increased risk of uterine scar rupture in labour following previous lower segment caesarean section, a retrospective cohort study (1988-91) was done to analyse active phase partographs of 236 patients undergoing trial of labour following caesarean section, 7 (3%) of whom had scar rupture. After onset of active phase (3 cm cervical dilatation), a 1 cm/h line was used to indicate "alert". A zonal partogram was developed by dividing the active phase partographs into 5 time zones: A (area to the left of "alert" line), B (0-1 h after "alert" line), C (1-2 h after "alert" line), D (2-3 h after "alert" line) and EF (> 3 h after "alert" line). The relative risk of uterine scar rupture was calculated for different partographic time zones. The relative risk of uterine scar rupture was 10.5 (95% confidence interval 1.3-85.5, p = 0.01) at 1 hour after crossing the "alert" line; 8.0 (95% confidence interval 1.6-40.3, p = 0.009) at 2 hours after crossing the "alert" line; and 7.0 (95% confidence interval 1.6-29, p = 0.02) at 3 hours after crossing the "alert" line. In women undergoing trial of labour following caesarean section, prolonged active phase of labour is associated with increased risk of uterine rupture. A zonal partogram may be helpful in assessing this risk in actively labouring women who cross the partographic "alert" line.