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Surveillance of extreme obesity in pregnancy

Principal investigator
Marian Knight (NPEU)
Peter Brocklehurst (NPEU), Jenny Kurinczuk (NPEU)
Obesity, Severe maternal morbidity and mortality
Department of Health
Start year
End year
NPEU Contact
Marian Knight


Obesity is now recognised to be an important public health problem throughout the developed world. Obesity is rising rapidly in the UK in all age groups, including women of reproductive age. The proportion of women aged 25-34 with severe obesity (equivalent to a weight of about 110Kg in a woman of average height) has increased from 1.3% in 1994 to 2.2% in 2004. Retrospective database analyses in Canada , Australia and the UK have identified a number of risks associated with pregnancy among obese women. Women are at risk of a number of complications of pregnancy, including pre-eclampsia (high blood pressure and protein in the urine), blood clots and diabetes, and have higher rates of labour induction, delivery by caesarean section, general anaesthesia and anaesthetic complications. Obese women are also at increased risk of poor pregnancy outcomes, including stillbirth and neonatal death. Recent reports of the UK Confidential Enquiry into Maternal Deaths have also highlighted obesity as a factor in increasing numbers of maternal deaths in the UK. The majority of current studies focus on women with moderate obesity; the aim of this study was to investigate the management and outcomes of women who were extremely obese (BMI 50 kg/m2 or greater).

Key findings

  • Nearly one in every thousand women giving birth in the UK is extremely obese, defined as a BMI of 50kg/m2 or greater.
  • These women are at risk of a number of severe morbidities, including pre-eclampsia (aOR 4.46, 95%CI 2.43-8.16), gestational diabetes (aOR 7.01, 95%CI 3.56-13.8), and intensive care unit admission (aOR 3.86, 95%CI 1.41-10.6).
  • Obese women were also more likely to have interventions which put them at risk of severe morbidity, including caesarean delivery (aOR 3.50, 95%CI 2.72-4.51) and general anaesthesia (aOR 6.35, 95%CI 2.63-15.3).
  • Basic equipment was not universally available for the care of these women, and this, together with the increase in prevalence of obesity, has important implications for maternity service provision. There is a need to address pre-pregnancy care and weight management programmes to prevent this increase in prevalence as well as to ensure appropriate services are in place to reduce the inequalities in pregnancy outcomes for these women.
  • After adjustment, there were no significant differences in anaesthetic, postnatal or neonatal complications between women with planned vaginal delivery and planned caesarean delivery, with the exception of shoulder dystocia (3% versus 0%, p=0.019). None of the infants born following shoulder dystocia were reported to have any long term complications.
  • There were no significant differences in any outcomes in the subgroup of women who had no identified medical or antenatal complications.
  • This study does not, therefore, provide any evidence to support a routine policy of caesarean delivery for extremely obese women on the basis of concern about higher rates of delivery complications, but does support a policy of individualised decision-making on the mode of delivery based on a thorough assessment of potential risk factors for poor delivery outcomes.


Journal Articles