The 2001 study... (BMJ 2001;322:1330) (Highlighting is my own and i have picked relevant parts of the text. Link to full article here )
Objectives: To audit interval from decision to delivery in urgent caesarean section to determine whether the current standard of 30 minutes is achievable routinely; to determine whether delay leads to an excess of admissions to special care.
Results: In the continuous audit 478 of 721 (66.3%) women were delivered in 30 minutes and 637 (88.3%) within 40 minutes; 29 (4.0%) were undelivered at 50 minutes.
Conclusions: The current recommendations for the interval between decision and delivery are not being achieved in routine practice. Failure to meet the recommendations does not seem to increase neonatal morbidity.
When an urgent caesarean section is performed, it is widely advocated that the interval between the decision to operate and delivery of the baby should be less than 30 minutes. The recommendation states that a unit should be able to be ready to perform a caesarean section within 30 minutes, implying that the interval between decision and delivery may be a little longer
Fewer babies were admitted to special care when the interval between decision and delivery was shorter, but not when prematurity was excluded as a reason for admission to special care
The numbers in this audit indicate that delay is an unusual cause of neonatal problems. It could be that the time taken to deliver makes no difference. This is scientifically unlikely, as a compromised baby is going to deteriorate if left in an unfavourable environment. However, it may be that for the most part a baby can recover from any additional compromise caused by the delay. Delays of up to 50 minutes seem to be an unlikely cause of problems for an infant.
Some more recent stats on this (Pearson et al 2011 link )
68% Category 1 deliveries were achieved within 30min and 66% Category 2 within 75min
8% Category 1 and 4% Category 2 neonates were acidotic or asphyxiated. The risk of acidosis was not reduced by delivery within 30min for Category 1 (OR 0.56; 0.11–2.81), or within 75min for Category 2 (OR 2.72; 0.6–25.1).
Conclusions
Our data suggest that clinical triage is effective, with the more compromised fetus delivered more rapidly using general anaesthesia. For Category 1 deliveries a 30min target DDI is appropriate, although those born after longer DDI did not show developmental impairment.
Current NICE guidelines on unplanned C section decision to delivery intervals;
1.4.3.1 Perform category 1 and 2 CS2 as quickly as possible after making the decision, particularly for category 1. [new 2011]
1.4.3.2 Perform category 2 CS2 in most situations within 75 minutes of making the decision. [new 2011]
1.4.3.3 Take into account the condition of the woman and the unborn baby when making decisions about rapid delivery. Remember that rapid delivery may be harmful in certain circumstances. [new 2011]
Most recent stats (England NHS births 2012/13)
Unplanned C section was 13% of all births over 37 weeks
Unplanned C section was 1% of all birth episodes where the duration of delivery episode was 1 day or less (it is 25% where the duration of the delivery episode is 2 + days)