Ethnicity, body mass index and risk of pre-eclampsia in a multiethnic New Zealand population.

Background: Pre-eclampsia rates are reported to vary by ethnicity; however, few studies include body mass index (BMI). Increasing BMI has a dose-dependent relationship with pre-eclampsia, and rates of overweight and obesity as well as ratios of body fat to muscle mass differ between ethnicities. We hypothesised that after adjusting for confounders, including ethnic-specific BMI, ethnicity would not be an independent risk factor for pre-eclampsia. Aim: To assess independent pre-eclampsia risk factors in a multiethnic New Zealand population. Methods: We performed a retrospective cohort analysis of prospectively recorded maternity data from 2006 to 2009 at National Women's Health, Auckland, New Zealand. After exclusion of infants with congenital anomalies and missing data, our final study population was 26 254 singleton pregnancies. Multivariable logistic regression analysis adjusted for ethnicity, BMI, maternal age, parity, smoking, social deprivation, diabetes, chronic hypertension and relevant pre-existing medical conditions was performed. Results: Independent associations with pre-eclampsia were observed in Chinese (adjusted odds ratio (aOR) 0.56, [95% CI 0.41-0.76]) and Maori (aOR 1.51, [1.16-1.96]) compared with European women. Other independent risk factors for pre-eclampsia were overweight and obesity, nulliparity, type 1 diabetes, chronic hypertension and pre-existing medical conditions. Conclusions: Contrary to our hypothesis, we report an independent reduced risk of pre-eclampsia in Chinese and increased risk of pre-eclampsia in Maori women. Prospective studies are required to further explore these relationships. Other independent risk factors are consistent with international literature. Our findings may assist clinicians to stratify risk of pre-eclampsia in clinical practice.