Our findings suggest that WC, prior to pregnancy, is the best anthropometric predictor of GHD in Aboriginal women. All five indices are positively associated with GHD, and can be used to predict GHD several years prior to pregnancy. However, only the associations of BMI and WC with GHD are statistically significant, before and after adjusting for confounding factors. Moreover, women with high BMI before pregnancy have over twice the odds of experiencing GHD during pregnancy.
Although there are a number of studies have reported the impact of BMI, both before and during pregnancy, on GHD [14, 15, 21], the associations of anthropometric measurements, other than BMI, several years before pregnancy with GHD have not been well reported. Aboriginal Australians are more likely to experience pregnancy related complications [22, 23]; and they also tend to be obese in young adulthood . Therefore, understanding the associations of GHD with different anthropometric measurements, prior to pregnancy, is potentially a useful method to identify high risk individuals . This study is the first that assessed the associations of five anthropometric measurements prior to pregnancy with GHD, in Aboriginal women. Moreover, the data used in this study were obtained from a cohort with up to 20 years of follow-up, and the anthropometric measurements were undertaken several years (mean = 7 years) prior to pregnancy. Therefore our findings could be valid evidence in terms of the impacts of WC and BMI several years prior to pregnancy on GHD.
Campbell et al. have also assessed the impact of WC and BMI before pregnancy on the development of gestational hypertension . Their results, similar to ours, showed significant associations of WC and BMI with GHD. The current study is also comparable with a study undertaken by Lake et al. In their study, the impact of BMI before pregnancy on development of GHD was determined among women who became pregnant by the age of 33 . In that study, BMI measurements were carried out twice, at seven and 23 years of age. Their results showed a positive association between obesity at the age of seven and GHD. Lake et al. also reported a positive association between obesity at the age of 23, among women who experienced pregnancy by the age of 33, and GHD, independent of their BMI at the age of seven .
Ijuin et al. have investigated the association between upper/lower-half-body ratio (body-fat amount ratio) and pre-eclampsia. Their findings could be comparable with ours in regard to association between WHR and GHD. According to their study, upper/lower-half-body ratio is associated with pre-eclampsia . Both studies showed a positive association and a very large unadjusted point estimate. However, our findings did not show a significant association between WHR and GHD after adjusting for confounding factors. Furthermore, their results showed a weak association between BMI and pre-eclampsia, whereas a number of studies including ours showed a strong association even after adjusting for other risk factors.
In this study all participants were from a relatively homogenous Aboriginal community, which simplified the comparison between cases and controls, although there are no standardised BMI or WC cut-off points for this population.
One of the limitations of this study was its small sample size. In addition, because the number of missing data for some of the measurements (e.g. WHR, WHtR) was higher than the number of missing BMI data, the related assessments had a smaller sample-size than the original study groups, which reduced the related statistical power. In addition, because women with GHD in this study were identified through hospital records, minor GHD cases might had not been hospitalised, and misclassified as controls, which could have diluted the true associations between the anthropometric indices and GHD. There is also a possibility of human error in performing the anthropometric measurements. Since this study was conducted in one remote community, the generalisability of our findings to other Aboriginal communities remains to be verified.