The circadian rhythm of "urgent" operative deliveries

Even operative deliveries defined as "urgent" show marked diurnal variation with a significant increase during regular working hours.

To investigate the diurnal variation of urgent operative deliveries and its potential implications on the outcome of newborns.

We conducted a retrospective study of all deliveries in a public hospital from 1 January 1990 to 31 December 1998. Delivery mode variables analyzed were spontaneous vaginal delivery, urgent cesarean section and operative vaginal delivery. Deliveries were stratified hourly throughout the day. The rate of operative deliveries was calculated and the analysis was then performed according to the daily routine shifts of the medical staff. Birth weight and Apgar scores at 1 and 5 minutes were retrieved as outcome measures.

The rate of urgent cesarean deliveries increased significantly between 8 a.m. and 2 p.m. (150%-230%) from that predicted. The lowest rate of urgent cesarean sections was found between 5 a.m. and 6 a.m. (5.3%). Mean birth weight in spontaneous deliveries was higher in the morning hours than during the night shift (3,293 +/- 520 g vs. 3,277 +/- 510 g, respectively, P < 0.005). Apgar scores of newborns delivered by urgent cesarean section during the morning were higher compared to those delivered during night shifts and the rate of low Apgar scores was lower in the morning than in evening and night shifts.

Our results indicate a marked diurnal variation in urgent operative deliveries, caused perhaps by varying definition of "urgency" according to the time of day.