Empirically derived relationships between body size variables and cardiac dimensions have not been published previously for a large sample of male and female athletes. This process would inform scaling practice and facilitate intra- and inter-group comparisons of cardiac data. Therefore we investigated the relationships of body mass (BM), height and body surface area (BS) with a range of cardiac dimensions derived by echocardiography in 464 male and female elite junior athletes (age range 14-18 years; sporting allocation included rowers, cyclists, footballers, tennis players, swimmers and a miscellaneous group). Initial linearity checks suggested that most of the relationships between the body size variables and cardiac dimensions were non-linear, thus precluding the simple ratio standard approach to scaling. Multiple log-log least-squares linear regression confirmed commonality of slopes (between males and females, across the age range and between sporting groups) for all relationships involving BM and BS. Subsequent analyses of the slope exponent (b) for left ventricular dimensions supported previous data and were dimensionally consistent (LVM-BM, b=0.91+/-0.11; LVM-BS, b=1.44+/-0.19; where LVM is left ventricular mass), except for left ventricular internal dimension in diastole (LVIDd) (LVIDd-BM, b=0.25+/-0.04). Data for the left atria internal dimension (LA) were also dimensionally consistent (LA-BM, b=0.29+/-0.09); however, this was not the case for the right ventricular internal dimension in diastole (RVIDd) (RVIDd-BM, b=0.76+/-0.14). It is possible that these results were due to a study-specific limitation in the data range (LVIDd) and the geometric peculiarities of RVIDd compared with LVIDd. The gender/age/sporting groupxbody size interaction factor for virtually all relationships between height and cardiac dimensions was significant (P<0.05), and thus whole-group b exponents could not be generated. Generally these data support previous small-sample research with athletes, and suggest that allometric scaling, as opposed to simple ratio scaling, should be adopted in studies of cardiac dimensions in athletes. This should allow, with minimal mathematical difficulty, the production of body-size-independent cardiac indices to be evaluated in laboratory or clinical work. Further research is required to develop normative 'allometrically derived' cardiac indices, and care should be taken to determine relationships in specific population groups as well as to confirm commonality of slopes in multiple group comparisons. Caution is expressed regarding the use of height as a scaling variable in future research.

Introduction International evidence shows that Asians have increased diabetes risk at a lower body mass index (BMI) than European Whites.1 UK guidance for routine gestational diabetes screening does not consider this BMI difference in risk. A proportion of high risk Asian women are therefore unscreened for diabetes in pregnancy, and potentially wrongly assigned to low risk care leading to inequalities. This study describes trends in first trimester obesity using the WHO BMI criteria for Asians. Methods Retrospective epidemiological study using data from 34 maternity units in England between 1995 and 2007. Obesity classification was BMI >27.5 kg/m2 for Asians, and >30 kg/m2 for all other ethnic groups. χ2 analyses were used for trends over time. Logistic regression for odds of first trimester obesity among ethnic groups adjusted for maternal age, parity, deprivation and employment. Results Black and South Asian women have a significantly higher incidence of first trimester obesity compared with White women, and this is increasing at a more rapid rate over time in Black women. The proportion of South Asian women classified as obese doubled from 10.6% to 20.5% when using the WHO criteria for Asians compared with the general population BMI. Following adjustment for population demographics, Pakistani women had the highest odds of first trimester obesity (OR 2.19, 95% CI 2.08 to 2.31). Conclusion Current gestational diabetes screening in the UK excludes half of the South Asian population at high risk. There should be further consideration of ethnic groups when defining the BMI categories to be used when developing clinical guidelines and services.

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