Risk of eclampsia or HELLP-syndrome by institution availability and place of delivery - A population-based cohort study

Objective: To examine the association between availability of obstetric institutions and risk of eclampsia, HELLP-syndrome, or delivery before 35 gestational weeks in preeclamptic pregnancies. Study design: National population-based retrospective cohort study of deliveries in Norway, 1999-2009 (n = 636738) using data from The Medical Birth Registry of Norway and Statistics Norway. Main exposures were institution availability, measured by travel time to the nearest obstetric institution, and place of delivery. We computed relative risks (RR) with 95% confidence intervals (CI) using travel time <= 1 h as reference. We stratified analyses by parity and preeclampsia, and adjusted for socio-demographic and medical risk factors. Successive deliveries were linked using the national identification number. Results: We identified 1387 eclampsia/HELLP cases (0.2%) and 3004 (0.5%) deliveries before 35 weeks in preeclamptic pregnancies. Nulliparous women living > 1 h from any obstetric institution had 50% increased risk of eclampsia/HELLP (0.50 versus 0.35%, adjusted RR 1.5; 95 %CI 1.1-1.9). Parous women living > 1 h from emergency institutions had a doubled risk of eclampsia (0.6 parts per thousand versus 0.3 parts per thousand, adjusted RR 2.0; 1.2-3.3). Women without preeclampsia in the present pregnancy or history of preeclampsia constituted all eclampsia/HELLP cases in midwife-led institutions, 39-50% of cases in emergency institutions, and 78% of cases (135/173) in subsequent deliveries. Women with risk factors delivered in the emergency institutions, indicating well-implemented selective referral. Conclusion: The study shows the importance of available obstetric institutions. Policymakers and clinicians should consider the distribution of potential benefits and burdens when planning and evaluating the obstetric health service structure.