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The association between maternal size and outcomes for women undergoing for caesarean section: a multicentre prospective observational study (The MUM SIZE Study)
Board Board 1 / Wed 12:35, 11 May 2016

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Obesity is defined by World Health Organization (WHO) as a body mass index (BMI) of ≥ 30 kg.m-2. Obesity rates in women of childbearing age are increasing and this is thought to contribute to adverse pregnancy outcomes.1-3 During pregnancy, however, BMI may naturally increase leading to incorrect classification of term women according to WHO BMI categories and a reluctance of clinicians and researchers to use these BMI categories at term. Also, the rate of caesarean section is increasing which, when combined with increased BMI, may lead to adverse maternal and neonatal outcomes, increased theatre times and increased hospital costs.  There is little research in this area. Our aim was to investigate associations between maternal size (using term pregnancy specific BMI cut-off values which were 5 kg.m-2 higher in each WHO category), and clinical, theatre utilization and health economic outcomes for women having caesarean section.


Following ethics approval, consent and trial registration (ACTRN1261300060876) we undertook a prospective multicentre observational study in women undergoing all categories of caesarean section. We recorded BMI at initial antenatal visit and delivery. Linear regression models accounting for clustering within hospitals and confounders, and health economic models were used to analyse associations between delivery BMI and total theatre time, surgical and anaesthesia times, maternal and neonatal adverse outcomes, total hospital costs, and theatre costs.


1505 women were recruited from a total of 1978 eligible participants (76%). The final sample size was 1457 participants (97% of the recruited number of women). Mean gestation was 38 weeks. Mean BMI increase (booking to delivery) was 4.0 kg.m-2. For each unit BMI increase total theatre time increased by 0.6 min (minutes) (p<0.001). Approximately 1 in 20 women were super-obese (BMI ≥ 45 kg.m-2) and they had a 30% (17 min) longer total theatre time (p<0.001), 20% (8 min) longer surgical time (p<0.001) and a 40% (10 min) longer anaesthesia time (p<0.001) compared with normal BMI (23.5 - < 30 kg.m-2) women. Increased delivery BMI was associated with increased risk of maternal intensive care unit (ICU) admission (OR=1.07, p=0.046) but no increase in neonatal admission to higher acuity care (HDU). Total hospital, and theatre costs were increased by 15% (p=0.032) and 27% (p=0.001) respectively in super-obese compared to normal BMI women.


High BMI is associated with increased total theatre time, surgical and anaesthesia time, increased maternal risk of ICU admission and increased total hospital and theatre costs. These clinical risks, time impacts and costs need to be considered in pregnant women. To do so we must record maternal BMI at term.

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