Audit of the influence of body mass index on the performance of epidural analgesia in labour and the subsequent mode of delivery.

OBJECTIVE: To assess the influence of body mass index (BMI) on the performance of epidural analgesia in labour and the subsequent mode of delivery.

DESIGN: A retrospective audit of prospectively collected quality assurance data.

SETTING: The delivery suite of Leeds General Infirmary, Leeds, UK. This is a 4500-delivery teaching hospital unit.

POPULATION: All women receiving epidural analgesia during labour in our unit between April 1997 and December 2005.

METHODS: Epidural recipients were divided into BMI groups according to World Health Organization (WHO) categories and compared for indices of epidural performance and mode of delivery.

MAIN OUTCOME MEASURES: Midwife and patient satisfaction scores with epidural analgesia, epidural resite rates, and mode of delivery.

RESULTS: Data from 13 299 epidural recipients were analysed. Using WHO definitions, 22.8% were of normal body mass, 41.9% were overweight, 31.9% obese, and 3.4% morbidly obese. Epidurals were more likely to fail as BMI increased, as judged by midwife satisfaction scores (P < 0.001) and epidural resite rates (P < 0.01). This trend was not seen for maternal satisfaction scores using the WHO BMI categories. However, if women with BMI below 30 kg/m2 were grouped together, a significant trend was found (P < 0.01). BMI had no influence on vaginal instrumental deliveries, but caesarean section rates rose from 11.5% in women of normal BMI to 29.2% in the morbidly obese women (P < 0.001).

CONCLUSIONS: Obesity increases the incidence of analgesic failure and the need for resite of epidurals. The caesarean section rate among epidural recipients increases dramatically as BMI rises.