ObjectiveTo generate a global reference for caesarean section (CS) rates at health facilities.DesignCross‐sectional study.SettingHealth facilities from 43 countries.Population/SampleThirty eight thousand three hundred and twenty‐four women giving birth from 22 countries for model building and 10 045 875 women giving birth from 43 countries for model testing.MethodsWe hypothesised that mathematical models could determine the relationship between clinical‐obstetric characteristics and CS. These models generated probabilities of CS that could be compared with the observed CS rates. We devised a three‐step approach to generate the global benchmark of CS rates at health facilities: creation of a multi‐country reference population, building mathematical models, and testing these models.Main outcome measuresArea under the ROC curves, diagnostic odds ratio, expected CS rate, observed CS rate.ResultsAccording to the different versions of the model, areas under the ROC curves suggested a good discriminatory capacity of C‐Model, with summary estimates ranging from 0.832 to 0.844. The C‐Model was able to generate expected CS rates adjusted for the case‐mix of the obstetric population. We have also prepared an e‐calculator to facilitate use of C‐Model (www.who.int/reproductivehealth/publications/maternal_perinatal_health/c-model/en/).ConclusionsThis article describes the development of a global reference for CS rates. Based on maternal characteristics, this tool was able to generate an individualised expected CS rate for health facilities or groups of health facilities. With C‐Model, obstetric teams, health system managers, health facilities, health insurance companies, and governments can produce a customised reference CS rate for assessing use (and overuse) of CS.Tweetable abstractThe C‐Model provides a customized benchmark for caesarean section rates in health facilities and systems.

The difference in density between the cerebrospinal fluid (CSF) and local anaesthetic solutions should be considered as a means of restricting drug distribution in the subarachnoid space. Conventional spinal anaesthesia may not be suitable for routine use in outpatients and anaesthetists should familiarise themselves with techniques that are associated with a rapid recovery profile. Using a small dose of either hypobaric or hyperbaric local anaesthetic injected at low speed through a directed needle in patients lying in the lateral position for 15 to 30 minutes can result in preferential development of spinal anaesthesia on the operated side. Unilateral spinal anaesthesia may be indicated for short procedures involving only one of the lower limbs. Potential haemodynamic benefits have increased interest in methods achieving unilateral spinal anaesthesia, because hypotension is a common complication of spinal anaesthesia with larger doses of local anaesthetic 1. When haemodynamic change was compared between bilateral and unilateral spinal block from the same dose of hyperbaric bupivacaine (8 mg), the frequencies of hypotension were 22.4% and 5%, respectively 2. The advantages of unilateral or selective versus conventional subarachnoid anaesthesia are better haemodynamic stability 1,2,5,6 , faster motor and sensory recovery 2-4 and decreased urinary retention 3,4,6,7. Unilateral spinal anaesthesia is associated with a lower rate of cardiovascular complications due to less sympathetic block than bilateral spinal anaesthesia 5. The patients' satisfaction with the unilateral technique appears high 3,4,8,9. The rationale behind our approach was to produce spinal anaesthesia restricted to the operative side alone and to obtain surgical anaesthesia just sufficient for the duration of surgery. The primary