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OBJECTIVE: To estimate the prevalence and describe on a national basis the management and outcomes of extreme obesity (body mass index [BMI] 50 kg/m or higher) in pregnancy in the United Kingdom. METHODS: A national cohort study was undertaken. Extremely obese women (BMI 50 or higher) and a comparison cohort were identified using the UK Obstetric Surveillance System. Prevalence estimates were calculated with 95% confidence intervals (CIs). Data for obese and comparison women were compared using the chi test or the Wilcoxon rank sum test. Odds ratios were estimated throughout using unconditional logistic regression. RESULTS: There were 665 women with extreme obesity in an estimated 764,387 women delivering, representing an estimated prevalence of 8.7 cases per 10,000 deliveries (95% CI 8.1-9.4). Extremely obese women had more complications than did comparison women, including preeclampsia (9% of women in the case group, 2% of those in the comparison group), gestational diabetes (11% of women in the case group, 2% of those in the comparison group), preterm delivery (10% of women in the case group, 7% of those in the comparison group), general anesthesia (6% of women in the case group, 1% of those in the comparison group), and intensive care unit admission (3% of women in the case group, 1% of those in the comparison group). Fifty percent of extremely obese women had cesarean deliveries compared with 22% of women in the comparison group. No women died. CONCLUSION: Nearly 1 in every 1,000 women giving birth in the United Kingdom is extremely obese. These women have increased risks of poor outcomes. 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 an urgent need to address prepregnancy care and weight management programs to prevent this increase in prevalence, as well as to ensure that appropriate services are in place to reduce the inequalities in pregnancy outcomes for these women.

Original publication




Journal article


Obstet Gynecol

Publication Date





989 - 997


Adult, Body Mass Index, Cesarean Section, Female, Humans, Hypertension, Pregnancy-Induced, Logistic Models, Obesity, Pregnancy, Pregnancy Complications, Pregnancy Outcome, Prevalence, United Kingdom, Young Adult