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.