Fetal distress is an emergency condition requiring rapid caesarean delivery. Hence, it has been recommended that the decision-to-delivery interval should be within 30 mins. Many previous studies have failed to show any improved outcome with short decision-to-delivery interval. The reasons are (1) most of these studies were of small scale and retrospective with limitation in design; (2) the indications for caesarean deliveries recruited in these studies were not specific for life-threatening fetal distress; (3) selection bias as clinicians tended to deliver worse cases more quickly than less severe cases; (4) correlation was analysed between adverse fetal outcome and decision to delivery interval, but ignored the bradycardia-to-delivery interval, which reflected the actual duration of fetal hypoxia. Latest studies indeed have shown that bradycardia-to-delivery interval correlated significantly with arterial pH and base excess in life-threatening fetal conditions. The longer the bradycardia-to-delivery, the poorer the arterial blood gases parameters and neonatal outcomes. This result supports that every obstetric unit should have the capability to accomplish emergency caesarean section in 30 mins of decision for fetal safety. The Royal College of Obstetrics and Gynaecology has standardised the classification of the urgency of caesarean delivery, which helps to identify those life-threatening fetal conditions that will be benefited from rapid delivery. Training in teamwork and communication, availability of anaesthetists, and operation theatre are the main factors to achieve a quick caesarean delivery.
Introduction
Fetal distress is one of the major indications for caesarean section in modern obstetrics. The duration of in-utero fetal hypoxia is regarded as the crucial factor for the development of permanent fetal hypoxic ischaemic brain damage. Hence, it has been advocated that delivery should be as quick as possible once fetal distress is diagnosed. Many professional organisations have also set guidelines that the delivery of the baby should be accomplished within 30 mins after decision of caesarean section, and made this 30-min rule as an auditing standard. Therefore, decision-to-delivery interval (DDI) and decision-to-incision interval (DII) are commonly used terms in audit or research.
Although such a proposal seems sensible, it has remained controversial over the past 2 decades, as strong clinical evidence is lacking to support the notion that a short DDI or DII is associated with improved perinatal outcomes. Furthermore, many obstetrics units have shown that emergency delivery is often not achievable within 30 mins in reality. New research, however has provided insight into this issue. In addition, to avoid the confusion caused by using different terminology such as ‘crash’, ‘urgent’ and ‘emergency’ caesarean section to describe the same category of caesarean section ( Tables 1 and 2 ), the Royal College of Obstetrics and Gynaecology (RCOG) has recently standardised the terminology and classification of urgency of caesarean sections ( Table 3 ). In this review, the origin of the 30-min rule, as well as the evidence to support or challenge this rule, are reviewed. In addition, the practical issue on how to achieve a quick delivery will also be discussed.
Grade | Term | Definition |
---|---|---|
1 | Emergency | Immediate threat to life of woman or fetus. |
2 | Urgent | Maternal or fetal compromise that is not immediately life-threatening. |
3 | Scheduled | Needing early delivery but no maternal or fetal compromise. |
4 | Elective | At a time to suit the women and maternity team. |
Term | Definition |
---|---|
Emergency | Decision made in labour for evolving fetal distress, failing labour or maternal reasons. |
Crash | Decision made if impending fetal death or serious maternal compromise anticipated (e.g. cord prolapse, abruption, uterine rupture). |
Urgent | Decision made during the 24 h before delivery because of deteriorating fetal or maternal health before the onset of labour. |
Pre-empted | Decision made more than 24 h before the onset of spontaneous labour or membrane rupture. |
Category | Definition |
---|---|
1 | Immediate threat to life of woman or fetus. Includes caesarean section for acute severe bradycardia, cord prolapse, uterine rupture, fetal blood sampling pH less than 7.2. |
2 | Maternal or fetal compromise that is not immediately life-threatening. There is ‘urgency’ to deliver the baby in order to prevent further deterioration of either the mother or baby’s condition (e.g. antepartum haemorrhage, ‘failure to progress’ in labour with maternal or fetal compromise). |
3 | No maternal or fetal compromise but needs early delivery. Includes caesarean section carried out where there is no maternal or fetal compromise but early delivery is necessary (e.g. a woman booked for planned caesarean section who is admitted with pre-labour spontaneous rupture of membranes or ‘failure to progress’ with no maternal or fetal compromise). |
4 | Delivery timed to suit woman or staff. Includes all caesarean sections carried out ‘electively’ at a planned time to suit the mother and clinicians. |
a The Royal College of Obstetrics and Gynaecology recommend to: (1) Carry out category 1 and 2 caesarean section as quickly as possible after making the decision, particularly for category 1; (2) carry out category 2 caesarean section in most situations within 75 mins of making the decision; (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.
The origins of the 30-minute rule
A few early studies in the last century evaluated the DDI time for emergency caesarean section. In the 1950s, Halsey and Douglas reported that the average DII was 43 mins, whereas Choate and Lund reported in 1968 a median DDI of 12 mins, and recommended that delivery should be achieved within 15 mins. In one-third of their deliveries, the DDI exceeded 15 mins and, in 14%, even more than 30 mins were required. According to Boehm in the fifth edition of Standards for obstetrics and gynecology published by the American College of Obstetricians and Gynecologists (ACOG) in 1982, ‘An obstetric service that generally cares for high-risk patients should be staffed and equipped to handle emergencies and to be able to begin cesarean delivery within 15 minutes.’
After the publication in 1987 of a nation-wide survey of 538 hospitals in the USA, which showed that almost all hospitals had the ability to carry out an emergency cesarean section within 30 mins, the 15-min rule was then changed to a 30-min rule in ACOG’s sixth edition of Standards for obstetric services published in 1988. This was also adopted jointly by the ACOG and the American Academy of Pediatrics in their second edition of the Guidelines for perinatal care in the same year. Subsequently, the RCOG, as well as other professional authorities, also adopted this standard, although the German Society of Obstetrics and Gynecology set the DDI at 20 mins. In the UK, the 30-min rule became a requirement by the Clinical Negligence Scheme for Trusts in 1999, and the Confidential Enquiry into Stillbirths and Deaths in Infancy recommended that obstetric units should carry out surveys of their DDI.
The scientific rationale to set the limit at 30 mins, however, has not been clearly stated in published research or critically reviewed, and hence Schauberger and Chauhan in their review commented that the 30-min rule ‘at best should be seen as a consensus of experts, not directly supported by clinical trials or experimental evidence’. Therefore, in the fifth edition of Guidelines for perinatal care published jointly by ACOG and the American Academy of Pediatrics in 2002, the emphasis was on the ‘capability’ to accomplish delivery in 30 mins, rather than as a ‘requirement’:
‘Any hospital providing an obstetric service should have the capability of responding to an obstetric emergency. No data correlate the timing of intervention with outcome, and there is little likelihood that any will be obtained. In general, however, the consensus has been that hospitals should have the capability of beginning a caesarean within 30 mins of the decision to operate.’
The distinction between ‘capability; and ‘requirement’ is crucial, as it would become a common reason for medico-legal claims if overlooked.
Although the ACOG and the American Academy of Pediatrics commented that it is unlikely to obtain data correlating the timing of intervention with perinatal outcome, some old animal experiments have shown that fetal cerebral damage would occur after a prolonged period of anoxia. For example, Faro and Windle in 1969 studied the effect of anoxia in a group of monkeys after umbilical cord occlusion, and concluded that a period of anoxia exceeding 10 mins could induce irreversible cerebral injury. Although the implication of this finding in animal experiments on the human fetus was not well addressed, this was indeed supported by case studies of fetal hypoxia caused by uterine rupture that indicated the occurrence of severe irreversible hypoxic ischaemic injury in the human fetus when the DDI was as short as 18 mins. On the other hand, a number of subsequently published observational studies that showed negative results has largely overturned the conclusion of this observation.
The origins of the 30-minute rule
A few early studies in the last century evaluated the DDI time for emergency caesarean section. In the 1950s, Halsey and Douglas reported that the average DII was 43 mins, whereas Choate and Lund reported in 1968 a median DDI of 12 mins, and recommended that delivery should be achieved within 15 mins. In one-third of their deliveries, the DDI exceeded 15 mins and, in 14%, even more than 30 mins were required. According to Boehm in the fifth edition of Standards for obstetrics and gynecology published by the American College of Obstetricians and Gynecologists (ACOG) in 1982, ‘An obstetric service that generally cares for high-risk patients should be staffed and equipped to handle emergencies and to be able to begin cesarean delivery within 15 minutes.’
After the publication in 1987 of a nation-wide survey of 538 hospitals in the USA, which showed that almost all hospitals had the ability to carry out an emergency cesarean section within 30 mins, the 15-min rule was then changed to a 30-min rule in ACOG’s sixth edition of Standards for obstetric services published in 1988. This was also adopted jointly by the ACOG and the American Academy of Pediatrics in their second edition of the Guidelines for perinatal care in the same year. Subsequently, the RCOG, as well as other professional authorities, also adopted this standard, although the German Society of Obstetrics and Gynecology set the DDI at 20 mins. In the UK, the 30-min rule became a requirement by the Clinical Negligence Scheme for Trusts in 1999, and the Confidential Enquiry into Stillbirths and Deaths in Infancy recommended that obstetric units should carry out surveys of their DDI.
The scientific rationale to set the limit at 30 mins, however, has not been clearly stated in published research or critically reviewed, and hence Schauberger and Chauhan in their review commented that the 30-min rule ‘at best should be seen as a consensus of experts, not directly supported by clinical trials or experimental evidence’. Therefore, in the fifth edition of Guidelines for perinatal care published jointly by ACOG and the American Academy of Pediatrics in 2002, the emphasis was on the ‘capability’ to accomplish delivery in 30 mins, rather than as a ‘requirement’:
‘Any hospital providing an obstetric service should have the capability of responding to an obstetric emergency. No data correlate the timing of intervention with outcome, and there is little likelihood that any will be obtained. In general, however, the consensus has been that hospitals should have the capability of beginning a caesarean within 30 mins of the decision to operate.’
The distinction between ‘capability; and ‘requirement’ is crucial, as it would become a common reason for medico-legal claims if overlooked.
Although the ACOG and the American Academy of Pediatrics commented that it is unlikely to obtain data correlating the timing of intervention with perinatal outcome, some old animal experiments have shown that fetal cerebral damage would occur after a prolonged period of anoxia. For example, Faro and Windle in 1969 studied the effect of anoxia in a group of monkeys after umbilical cord occlusion, and concluded that a period of anoxia exceeding 10 mins could induce irreversible cerebral injury. Although the implication of this finding in animal experiments on the human fetus was not well addressed, this was indeed supported by case studies of fetal hypoxia caused by uterine rupture that indicated the occurrence of severe irreversible hypoxic ischaemic injury in the human fetus when the DDI was as short as 18 mins. On the other hand, a number of subsequently published observational studies that showed negative results has largely overturned the conclusion of this observation.
Evidence opposing the 30-minute rule
After the introduction of the 30-min rule in the late 1980s and early 1990s, many retrospective studies have since challenged this rule owing to the unanimously negative finding of any improved perinatal outcome with a short DDI. Some of these studies even showed contradictory results, with a better or improved perinatal outcome in some cases, and delivery occurring beyond 30 mins compared with cases that were delivered within this time limit.
Chauhan et al. compared 61 cases of fetal distress delivered with a DII of 30 mins or less, with 56 cases where the DII was more than 30 mins, and found that the latter had a higher mean umbilical arterial pH (7.16 v 7.26), lower incidence of severe acidosis (pH < 7; 15% v 0%), and lower incidence of admission to neonatal intensive care unit (22.9% v 5.3%). The investigators attributed these better outcomes in the prolonged DII group to having more time for in-utero resuscitation by treatment modalities such as amnioinfusion or tocolytics. Interestingly, the authors had erroneously written in their abstract that ‘These adverse outcomes were observed more frequently in association with decision-incision time greater than 30 minutes’, which had misled their readers.
Mackenzie and Cooke, in their prospective cohort of about 400 women, reported that, as time between decision and delivery lengthened, there was a trend towards less acidaemia. The investigators postulated that the maternal anxiety generated by the decision for caesarean section might have provoked an increased release of maternal catecholamine, which might have, in turn, caused a reduction in placental perfusion and hence temporary fetal acidosis. The investigators, therefore, also doubted that the reliability of cord pH values as markers of fetal or neonatal wellbeing, and questioned the benefit of aiming to achieve delivery within 30 mins for all cases.
Similarly, Nasrallah et al. reported that, in a group of 83 neonates with DII of less than 30 mins, the incidences of cord pH less than 7.00, seizures, encephalopathy, and lower Apgar scores at 1 and 5 mins were higher than these respective outcomes in 28 neonates with DII of more than 30 mins. Maternal complication rate was also higher in the former group.
Bloom et al. conducted a much larger retrospective study comparing 1814 pregnancies with DDI 30 mins or less and 994 with DDI longer than 30 mins. The incidence of acidosis (pH < 7) was again higher in the former group (4.8% v 1.6%). Maternal complication rates, including endometritis, wound infection, and operative injury, were not related to DDI.
Thomas et al. on the other hand, examined the association between DDI and maternal and baby outcomes in a national cross-sectional survey of maternity units in England and Wales, and categorised the DDI according to less than 15 mins, between 15 and 75 mins, and over 75 mins. Among 17,780 singleton births delivered by emergency caesarean section between May and July 2000, no differences were found in maternal or neonatal outcome between the group with DDI within 15 mins and those with DDI between 16 and 75 mins. In the group with DDI after 75 mins, however, a significantly higher odds of a 5-min Apgar score of less than 7 was reported (OR 1.7, 95% CI 1.2 to 2.4), and a 50% increase in odds of special care was required in addition to routine care for mothers. Therefore, the investigators argued that DDI of 30 mins is not an absolute threshold for influencing baby outcome, but DDI of more than 75 mins should be avoided. The latest RCOG’s National Institute for Health and Clinical Excellence guideline also agreed with this view, and therefore recommended category 2 caesarean section to be carried out in most situations within 75 mins of making the decision.
Reports from two developing countries showed no significant relationship between poor neonatal outcome with prolonged DDI. In the prospective study from a tertiary centre in India, 121 out of 217 cases with emergency caesarean section had DDI at 30 mins or less. Compared with 96 cases with DDI over 30 mins, no significant differences were found in the incidences of low 5-min Apgar score and cord pH less than 7.10. The need for admission to NICU in the shorter DDI group, however, was significantly higher compared with the other group. In the study by Onah et al. from Nigeria, 164 women who underwent caesarean sections, and 60 women who underwent emergency caesarean sections were recruited from two hospitals, respectively. Their mean DDI, however, was 511 mins (range 45–5040 mins) and 201 mins (range 40–1050 mins), respectively, and none of these 224 cases had a DDI within the 30-min interval. With such a long DDI, it is not possible to draw any meaningful conclusion.
Reasons for lack of evidence to support the 30-minute rule
As caesarean section for fetal distress is an emergency, it is not possible to conduct a randomised-controlled trial to investigate the effect of the timing of the delivery on perinatal outcomes. Hence, the available evidence mostly consists of retrospective observational studies, for which we must interpret with caution.
The first major limitation of these kinds of studies is that some included emergency caesarean section for indications other than fetal distress, but for other non-life threatening conditions. For example, in the study by Thomas et al., which included the greatest sample size of 17,780 cases of emergency caesarean section, only 4622 (26%) were indicated for immediate threat to life of the woman or fetus, which is equivalent to Category 1 of RCOG’s classification of urgency of caesarean section ( Table 3 ). The effect of DDI on fetal outcome, if any, will be masked by most of the cases that did not have life-threatening conditions. Furthermore, in these studies, fetal distress was mostly diagnosed or suspected on the basis of continuous electronic fetal heart monitoring, a tool with high sensitivity but poor specificity for fetal hypoxia. Therefore, one would have expected a normal outcome for most cases delivered by emergency caesarean section, regardless of the length of DDI.
Secondly, clinicians often act more promptly in cases that they consider to be more severe, such as placental abruption, uterine scar rupture and cord prolapse. The DDI in these groups of cases will be shorter, but their risk of fetal hypoxia is also higher. On the other hand, when the fetal condition is less severe, the attending clinicians may allow a longer DDI. Therefore, this selection bias could give rise to a false impression of poor outcome with shorter DDI in some studies. To overcome this bias, we must focus only on those life-threatening cases, or cases with a more specific sign of fetal hypoxia (i.e. persistent fetal bradycardia).
Only a few studies, however, have attempted to address specifically cases with life-threatening conditions or Category 1 urgency ( Table 3 ). Hillemanns et al. included 109 cases with fetal bradycardia, but failed to demonstrate any temporal relationship between adverse fetal outcome and DDI. The possible explanation for this negative finding might be that the irreversible causes of fetal distress, such as cord prolapse and placental abruption, only contributed to 40% of cases and, in 26% of cases, the cause of fetal distress was unknown. It is likely that some causes of fetal distress, such as uterine hyperstimulation or post-regional anaesthetic effect, were reversible or have only a transient adverse effect. By the time the babies were delivered by caesarean section, the hypoxic condition had been resolved. Therefore, the possible adverse effects related to prolonged DDI among cases with irreversible causes would have been diluted by those cases with reversible elements. Kayani et al. analysed 33 cases with placental abruption. The investigators did find a significant improvement in fetal outcome in those babies delivered within 20 mins of decision, compared with those delivered later. Tan et al. focused on cases requiring crash caesarean section for umbilical cord prolapse, which was an irreversible cause for fetal hypoxia. No correlation was found between pH and DDI, most probably because the investigators could only recruit 14 participants, which was too few to show any statistical significance.
Finally, all the studies have investigated the perinatal outcome with DDI. The onset of fetal hypoxia, however, does not start at the time of decision but around the time of the onset of fetal bradycardia. Therefore, any relationship between the perinatal outcomes and duration of fetal hypoxia would have been masked if the analysis was confined to the DDI alone, without consideration of the BDI.
New evidence
Leung et al. recently published a retrospective study to address all the above limitations. Among the 235 cases of emergency caesarean section for fetal bradycardia, the investigators retrospectively classified the underlying pathologies into irreversible, potentially reversible and unknown groups. The irreversible group included cord prolapse, placental abruption, uterine rupture, pre-eclampsia and failed instrumental delivery. The potentially reversible conditions included iatrogenic uterine hyperstimulation, post-regional anaesthesia, and aortocaval compression. Among those cases with irreversible cause of fetal bradycardia, the investigators clearly showed an inverse relationship between umbilical arterial pH and base excess with BDI. The arterial pH dropped by 0.011 per min of BDI. Interestingly, the investigators did not show any statistical relationship between the blood gases parameters and DDI, even in the group of irreversible causes. Furthermore, in the group of reversible and unknown causes, no relationship was found between blood gases parameters and BDI or DDI. The investigators also showed that, in the irreversible group, the mean BDI and DDI was 11 mins and 10 mins, respectively, which were significantly shorter than those in the other two groups (16 mins and 11 mins, respectively).
The results of this study clearly demonstrated the fallacy shown in the previous studies. First, clinical evidence showed that, in case of fetal distress caused by irreversible conditions, fetal condition does deteriorate with time, and swift delivery is essential in these situations. Second, the shorter BDI and DDI in the irreversible group indicated that the clinicians did decide and act more promptly with these diagnoses. On the other hand, in potentially reversible conditions, the clinicians tended to observe for a longer period of time before making any decision. The relative delay in delivery might have allowed more time for the babies to recover. Hence, by the time of delivery, the babies’ condition seemed to be better. This accounted for the selection bias in the previous studies.
The subsequent study by Kamoshita et al. also echoed the finding of Leung et al. They examined the effect of the interval between onset of sustained fetal bradycardia and caesarean delivery on long-term neonatal neurologic prognosis in 19 pregnancies, including five cases of umbilical cord prolapse, four cases of placental abruption, three cases of uterine rupture, one case of maternal respiratory failure and six cases of other causes. The mean BDI was 20.5 ± 8.9 mins, whereas the mean DDI was 11.4 ± 3.9 mins. The investigators also found that BDI but not DDI was inversely correlated with umbilical arterial pH at delivery. All the studies assessing the perinatal outcomes with DDI or DII are presented in Table 4 for comparison.
Authors | Year of publication | Year of study | Countries | Study design | Case mix | Case number (DDI and DII ≦30 mins v DDI and DII >30 mins unless specified otherwise) | Result (short DDI and DII group compared with long DDI and DII group) (Apgar scores unless specified otherwise) | Mean and median DDI and DII (mins) | DDI ≤ 30 mins (%) |
---|---|---|---|---|---|---|---|---|---|
Schauberger and Chauhan | 1994 | 1985–1991 | USA | Retrospective | Emergency caesarean section not specified. | 47 v 28 | Lower Apgar scores; no difference in maternal morbidity. | 29.1 | 63 |
Chauhan et al. | 1997 | 1991–1993 | USA | Retrospective | Emergency caesarean section fetal distress. | 61 v 56 | Lower Apgar scores; lower pH; more admission to neonatal intensive care unit. | 37.1 | 52 |
MacKenzie and Cooke | 2002 | 1996 | UK | Prospective | Emergency caesarean section fetal distress and non-fetal distress. | 100 fetal distress; 230 no fetal distress. | Lower pH. | Crash caesarean 27.4; fetal distress 42.9; non-fetal distress 71.1. | <40 |
Tan et al. | 2003 | 1992–2002 | Singapore | Retrospective | Crash caesarean for cord prolapse. | 34 | No correlation between DDI and pH (only 14 cases had pH). | 20 | 76 |
Nasrallah et al. | 2004 | 1999–2001 | USA | Retrospective | Non-reassuring fetal heart rate, umbilical cord prolapse, placental abruption, placenta previa with haemorrhage, or uterine rupture. | 83 v 28 | Trend of Low pH, low Apgar scores, more seizure and encephalopathy. | 20 | 72 |
Holcroft et al. | 2005 | 2001–2003 | USA | Retrospective | Emergency caesarean section non-reassuring cardiotocography. | 34 emergent; 83 urgent | pH positively correlated with DDI. | Emergent 23; urgent 36 | No data |
Hillemanns et al. | 2005 | 1988–1997 | Germany | Retrospective | Crash caesarean section; prolapsed cord (21%) and placental abruption (20%) were the most frequent reasons for emergency cesarean section but in one-quarter of cases (25.7%). | 109 | Apgar scores positively correlated with DDI; pH and DDI no significant correlation. | 10 | 100% |
Bloom et al. | 2006 | 1999–2000 | USA | Retrospective | Non-reassuring fetal heart rate, umbilical cord prolapse, placental abruption, placenta previa with hemorrhage, or uterine rupture | 1814 v 994 | Lower pH, more intubation in delivery room. | No data | 65 |
Thomas et al. | 2004 | 2000 | UK | Retrospective | All emergency caesarean sections divided into three groups: DDI < 15 mins; DDI 15–75 mins; DDI > 75 mins. | 17,780 | No difference between less than 15 mins group and 15–75 mins group; >75 mins group higher odds of low Apgar score and need of special care for mothers. | No data | No data |
Kayani et al. | 2003 | 1990–1999 | UK | Retrospective | Placental abruption. | 33 | Better neonatal outcome in babies delivered within 20 mins compared with those after. | No data | 88 in 30 min 55 in 20 min |
Onah et al. | 2005 | 2003 | Nigeria | Prospective | All emergency caesarean from two hospitals. | 224 (none of them within 30 mins). | No significant difference. | Respectively 511 and 201 in two different hospitals. | None |
Roy et al. | 2008 | 2002–2007 | India | Prospective | Non-reassuring fetal heart. | 121 v 96 | No difference in Apgar scores, pH but neonatal intensive care unit admission rate higher. | 38.2 | 56 |
Leung et al. | 2009 | 2005–2008 | Hong Kong | Retrospective | Crash caesarean section for fetal bradycardia. | 236; irreversible causes of fetal bradycardia 39; potentially reversible cause 22; unknown cause 174. | pH and base excess (BE) inversely correlated with bradycardia-to-delivery interval in the group with irreversible causes; no relationship between pH, BE and DDI in another group. | 11 | 100 |
Kamoshita et al. | 2010 | 2002–2003 | Japan | Retrospective | Crash caesarean section for fetal bradycardia. | 19 | pH inversely correlated with bradycardia-to-delivery. | 11.4 | No data |

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