Prepregnancy body mass index and other risk factors for early-onset and late-onset haemolysis, elevated liver enzymes and low platelets (HELLP) syndrome: a population-based retrospective cohort study in British Columbia, Canada

BACKGROUND: Obesity increases risk of pre-eclampsia, but the association with haemolysis, elevated liver enzymes and low platelets (HELLP) syndrome is understudied. OBJECTIVE: To examine the association between prepregnancy body mass index (BMI) and HELLP syndrome, including early-onset versus late-onset disease. STUDY DESIGN: A retrospective cohort study using population-based data. SETTING: British Columbia, Canada, 2008/2009-2019/2020. POPULATION: All pregnancies resulting in live births or stillbirths at ≥20 weeks' gestation. METHODS: BMI categories (kg/m²) included underweight (<18.5), normal (18.5-24.9), overweight (25.0-29.9) and obese (≥30.0). Rates of early-onset and late-onset HELLP syndrome (<34 vs ≥34 weeks, respectively) were calculated per 1000 ongoing pregnancies at 20 and 34 weeks' gestation, respectively. Cox regression was used to assess the associations between risk factors (eg, BMI, maternal age and parity) and early-onset versus late-onset HELLP syndrome. MAIN OUTCOME MEASURES: Early-onset and late-onset HELLP syndrome. RESULTS: The rates of HELLP syndrome per 1000 women were 2.8 overall (1116 cases among 391 941 women), and 1.9, 2.5, 3.2 and 4.0 in underweight, normal BMI, overweight and obese categories, respectively. Overall, gestational age-specific rates of HELLP syndrome increased with prepregnancy BMI. Obesity (compared with normal BMI) was more strongly associated with early-onset HELLP syndrome (adjusted HR (AHR) 2.24 (95% CI 1.65 to 3.04) than with late-onset HELLP syndrome (AHR 1.48, 95% CI 1.23 to 1.80) (p value for interaction 0.025). Chronic hypertension, multiple gestation, bleeding (<20 weeks' gestation and antepartum) also showed differing AHRs between early-onset versus late-onset HELLP syndrome. CONCLUSIONS: Prepregnancy BMI is positively associated with HELLP syndrome and the association is stronger with early-onset HELLP syndrome. Associations with early-onset and late-onset HELLP syndrome differed for some risk factors, suggesting possible differences in aetiological mechanisms.