Maternal BMI and diabetes in pregnancy: Investigating variations between ethnic groups using routine maternity data from London, UK

Abstract

ObjectiveTo investigate the ethnicity-specific association between body mass index (BMI) and diabetes in pregnancy, with a focus on the appropriateness of using BMI cut-offs to identify pregnant women at risk of diabetes.Study designAnalysis of routinely-collected data from a maternity unit in London, UK. Data were available on 53 264 women delivering between 2004 and 2012. Logistic regression was used to explore the association between diabetes in pregnancy and BMI among women of different ethnicities, and adjusted probability estimates were used to derive risk equivalent cut-offs. ROC curve analysis was used to assess the performance of BMI as a predictor of diabetes in pregnancy.ResultsThe prevalence of diabetes in pregnancy was 2.3% overall; highest in South and East Asian women (4.6% and 3.7%). In adjusted analysis, BMI category was strongly associated with diabetes in all ethnic groups. Modelled as a continuous variable with a quadratic term, BMI was an acceptable predictor of diabetes according to ROC curve analysis. Applying a BMI cut-off of 30 kg/m2 would identify just over half of Black women with diabetes in pregnancy, a third of White (32%) and South Asian (35%) women, but only 13% of East Asian women. The ‘risk equivalent’ (comparable to 30 kg/m2 in White women) threshold for South Asian and East Asian women was approximately 21 kg/m2, and 27.5 kg/m2 for Black women.ConclusionsThis study suggests that current BMI thresholds are likely to be ineffective for diabetes screening in South and East Asian women, as many cases of diabetes will occur at low BMI levels. Our results suggest that East Asian women appear to face a similarly high risk of diabetes to South Asian women. Current UK guidelines recommend diabetes screening should be offered to all pregnant South Asian women; extending this recommendation to include women of East Asian ethnicity may be appropriate.

Effects of maternal anthropometrics on pregnancy outcomes in South Asian women: a systematic review

“…The prevalence of diabetes in pregnancy was also estimated for each BMI cut‐off; results showed an increased risk of diabetes at all BMI points for South Asian women compared with White women . In addition, this study found that for South Asian women, the BMI with risk of GDM equivalent to 30 kg m −2 in White women was approximately 21 kg m −2 .…”

“…These parameters gave an indication of the proportion of the population with GDM in each ethnic group that was captured using each cut‐off. A BMI of 20 kg m −2 captured 95.2% of White women compared with 95.0% of South Asian women with GDM . All other BMI cut‐offs investigated captured a higher percentage of South Asian women with GDM than White women .…”

“…All other BMI cut‐offs investigated captured a higher percentage of South Asian women with GDM than White women . This ranged from 93.6% in South Asian women compared with 87.5% in White women at BMI 21.5 kg m −2 , and 34.7% in South Asian women compared with 32.1% in White women at BMI 30 kg m −2 . The prevalence of diabetes in pregnancy was also estimated for each BMI cut‐off; results showed an increased risk of diabetes at all BMI points for South Asian women compared with White women .…”

“…Thirteen studies reported data for maternal pre‐pregnancy weight, BMI, SFT and serum leptin levels . Nine reported an increased association with GDM for South Asian women compared with White women . Three found a decreased association .…”

“…Thirteen studies were from the UK (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39), three from Australia (40,41), two from Norway (42,43) and Canada (44,45), and one from USA (46) and Spain (47) ( Table 1). Some studies used more than one exposure: 21 studies used maternal anthropometric measurements as the exposure (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(43)(44)(45)(46)(47)(48) (group 1), three used gestational change in maternal anthropometrics as the exposure (31,42,47) (group 2) and two used a combination of pre-pregnancy anthropometrics and gestational change in anthropometrics (42, 43) (group 3). Of the studies that used maternal BMI as a categorical exposure (n = 7), only three studies applied BMI criteria for South Asian populations (29,46,48).…”