Existing maternal obesity guidelines may increase inequalities between ethnic groups: a national epidemiological study of 502,474 births in England

Abstract

Background: Asians are at increased risk of morbidity at a lower body mass index (BMI) than European Whites, particularly relating to metabolic risk. UK maternal obesity guidelines use general population BMI criteria to define obesity, which do not represent the risk of morbidity among Asian populations. This study compares incidence of first trimester obesity using Asian-specific and general population BMI criteria.

Method: A retrospective epidemiological study of 502,474 births between 1995 and 2007, from 34 maternity units across England. Data analyses included a comparison of trends over time between ethnic groups using Asian-specific and general population BMI criteria. Logistic regression estimated odds ratios for first trimester obesity among ethnic groups following adjustment for population demographics.

Results: Black and South Asian women have a higher incidence of first trimester obesity compared with White women. This is most pronounced for Pakistani women following adjustment for population structure (OR 2.19, 95% C.I. 2.08, 2.31). There is a twofold increase in the proportion of South Asian women classified as obese when using the Asian-specific BMI criteria rather than general population BMI criteria. The incidence of obesity among Black women is increasing at the most rapid rate over time (p=0.01).

Conclusion: The twofold increase in maternal obesity among South Asians when using Asian-specific BMI criteria highlights inequalities among pregnant women. A large proportion of South Asian women are potentially being wrongly assigned to low risk care using current UK guidelines to classify obesity and determine care requirements. Further research is required to identify if there is any improvement in pregnancy outcomes if Asian-specific BMI criteria are utilised in the clinical management of maternal obesity to ensure the best quality of care is provided for women irrespective of ethnicity.

Figure 1

A Comparison of First Trimester Obesity Incidence over Thirteen Years in England stratified by Maternal Ethnic Group. Legend: Maternal obesity is classified as a BMI >27.5kg/m² for Asian populations, and ≥30kg/m² for non-Asian populations.

Figure 2

A Comparison of First Trimester Maternal Obesity Incidence over Thirteen Years in England stratified for South Asian and White Ethnic Groups. Legend: Maternal obesity is classified as a BMI >27.5kg/m² for South Asian women, and ≥30kg/m² for White women.