Original Article Comparison of maternal abdominal subcutaneous fat thickness and body mass index as markers for pregnancy outcomes: A stratified cohort study Ashwin SURESH, 1 Anthony LIU, 2 Alison POULTON, 2 Ann QUINTON, 3 Zara AMER, 3 Max MONGELLI, 3 Andrew MARTIN, 4 Ronald BENZIE, 3 Michael PEEK 3 and Ralph NANAN 2 1 Melbourne Medical School, The University of Melbourne, Melbourne, Victoria, 2 Discipline of Paediatrics, Sydney Medical School – Nepean, The University of Sydney, Nepean Hospital, Penrith, 3 Discipline of Obstetrics, Gynaecology and Neonatology, Sydney Medical School – Nepean, The University of Sydney, Nepean Hospital, Penrith, and 4 National Health and Medical Research Council (NHMRC) Clinical Trials Centre, The University of Sydney, Sydney, New South Wales, Australia Background: Obesity in pregnancy is associated with a number of adverse outcomes. The effects of central versus general obesity in pregnancy have not been well established. Aim: To compare subcutaneous fat thickness (SFT) with body mass index (BMI) as a marker for pregnancy outcomes. Methods: A stratified retrospective cohort study was performed on 1200 pregnancies, selected from a total of 4862 nulliparous, nonsmoking women between 2006 and 2010. SFT was measured on routine ultrasound at 18–22 weeks gestation. BMI and SFT measurements were compared for estimating risks for obesity-related pregnancy outcomes using logistic regression adjusted for maternal age. Results: The median SFT was 18.2 mm (range 6.3–50.9 mm), the median BMI was 23.8 kg/m 2 (range 15.2–52.5), and the correlation between SFT and BMI was 0.53. For every 5 mm increase in SFT and every 5 kg/m 2 increase in BMI, the odds ratios for developing gestational diabetes mellitus were 1.40 (CI 1.22–1.61, P < 0.001) and 1.16 (CI 0.95–1.40, P = 0.1), for caesarean section 1.28 (CI 1.16–1.40, P < 0.001) and 1.16 (CI 1.05–1.28, P = 0.003), large for gestational age 1.28 (CI 1.16–1.47, P = 0.001) and 1.10 (CI 0.95–1.28, P = 0.16) and cumulative adverse obesity-related pregnancy outcomes 1.16 (CI 1.10–1.28, P = 0.002) and 1.05 (CI 0.95–1.16, P = 0.45), respectively. Conclusion: SFT at 18–22 weeks gestation is better than BMI as a marker for obesity-related pregnancy outcomes. As SFT is considered a surrogate measure for visceral fat, these results suggest that central obesity is a stronger risk factor than general adiposity in pregnancy. Key words: central adiposity, obesity, pregnancy, subcutaneous fat. Introduction Between 35 and 60% of women of reproductive age are considered to be overweight or obese in developed countries. 1 Maternal adiposity is associated with a range of adverse pregnancy outcomes. 2,3 To estimate maternal adiposity, clinicians generally use the body mass index (BMI). BMI is a measure of general adiposity and makes little reference to body fat distribution. 4 However, body fat distribution is highly relevant in assessing obesity-related outcomes 5,6 and is commonly categorised into central fat and peripheral fat. 7,8 Accordingly, central obesity correlates better with most obesity-related complications. 9 In contrast, peripheral obesity has been suggested to abrogate or even to be protective for some weight-related risks. 7 CT, MRI, body densitometry or waist-to-hip ratio are considered better markers for central obesity than BMI, but impractical as screening tools in pregnancy. 6 Alternatively, abdominal subcutaneous fat measurements can be used as a surrogate measure for central obesity, 10,11 as it correlates with a range of cardiovascular and metabolic risk factors. 6,12 The abdominal subcutaneous fat thickness (SFT) can readily and accurately be measured by ultrasound. 13 In most developed countries, ultrasound measurements are routinely performed on all pregnant women at 18– Correspondence: Dr Anthony Liu, Sydney Medical School – Nepean, The University of Sydney, Nepean Hospital Penrith, NSW 2750, Australia. Email: liua@wahs.nsw.gov.au Received 13 February 2012; accepted 28 June 2012. 420 © 2012 The Authors ANZJOG © 2012 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists Australian and New Zealand Journal of Obstetrics and Gynaecology 2012; 52: 420–426 DOI: 10.1111/j.1479-828X.2012.01471.x Te Australian and New Zealand Journal of Obstetrics and Gynaecology