Interpretation
The simple hierarchical classification system used in the study (Figure 1, Supplement 1) classifies intrapartum CS by the condition of the fetus, rate of progress during labour and the use of oxytocin in an inclusive and mutually exclusive manner.10, 12 This is in contrast to a systematic review of indication-based classifications9 which identified only two out of twelve studies using a mutually exclusive system 14, 15. Generally, this review found low reproducibility in classification (disagreement in 45% of the cases [range 8%-83%]). The studies utilizing a mutually exclusive classification 14, 15 incorporated some elements of the TGCS into their indication system (previous CS and breech), but did not differentiate between suspected fetal distress according to use or non-use of oxytocin and whether the suspected fetal distress was a primary factor or only occurred as a result of treatment of dystocia. Both types of suspected fetal distress were accounted for appropriately in the current study.
Detailed indications for intrapartum CS in Norway have been previously reported based on the mandatory data collection in the Medical Birth Registry of Norway.16-18 Interestingly an analysis of the period 1967-84, classified 31 indications into seven high level groups (mechanical, uterine, presentation, asphyxia, other fetal, maternal, acute placental). More than one category though was present in 35% of all CS.16
A comparison of Scotland, Sweden, USA and Norway during the time period 1980-90, chose the first relevant in a hierarchy of five indications (previous CS, breech presentation, dystocia, fetal distress, or other) as the primary indication and were classified accordingly. The number of CS with multiple indications was not reported. 17
A nationwide study in 1998-99 reported indications for CS using a pre-determined set of 31 indications with up to four choices per case.18 In all three studies the classification systems were also totally inclusive, but not mutually exclusive. Both the arbitrary hierarchy 17 and the subjectivity related to combinations among a set of indications 16, 18 make a comparison impossible. Moreover, there was no division of CS into those performed before and during labour and features characterizing women according to the TGCS (breech presentation, previous CS) were partly mixed with indications. 16-18
A Slovenian study applied a modified version of the ICSCS used in the current study on deliveries in the TGCS group 1. 19They found intrapartum CS classified as Dystocia-Efficient uterine action - CPD to be more prevalent as compared to Norway (3.1% vs. 0.2%). 19 Different clinical approaches to vaginal operative delivery could explain this: instrumental delivery was performed four times more frequently in Norway compared to Slovenia.20
In a Swedish registry-based study on women in TGCS Group 1 and 2a for the period 1999-2010 multiple indications accounted for 14% of all intrapartum CS and an indication was missing in as many as 18% of deliveries. 21
Other studies, based on either national or multicenter data did not apply indications within the TGCS and their subgroups,22, 23 making it impossible to differentiate pre-labour CS from those performed intrapartum. Multiple indications per CS were also common and while they might provide a more complete explanation of the clinical situation, they are not useful for classification, comparison and learning from each other.