Secular trends in the epidemiology of pre-eclampsia throughout 40 years in Norway: prevalence, risk factors and perinatal survival Kari Klungsøyr a,b , Nils Halvdan Morken c , Lorentz Irgens a,b , Stein Emil Vollset a,b and Rolv Skjærven a,b a Department of Public Health and Primary Health Care, University of Bergen, b Medical Birth Registry of Norway, The National Institute of Public Health, and c Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway Summary Correspondence: Dr Kari Klungsøyr, Department of Public Health and Primary Health Care, University of Bergen, Kalfarveien 31, 5018 Bergen, Norway. E-mail: kari.melve@isf.uib.no Klungsøyr K, Morken NH, Irgens L, Vollset SE, Skjærven R. Secular trends in the epidemiology of pre-eclampsia throughout 40 years in Norway: prevalence, risk factors and perinatal survival. Paediatric and Perinatal Epidemiology 2012; 26: 190–198. Pre-eclampsia is a leading complication of pregnancy, associated with maternal and neonatal morbidity. The present study describes the epidemiology of pre-eclampsia in Norway, with data from the Medical Birth Registry of Norway, covering 40 years. We aimed at describing time trends in prevalence, selected risk factors and perinatal mortality. We also analysed time trends in recurrence risk of total pre-eclampsia and pre-eclampsia with preterm delivery. A total of 2 416 501 women giving birth during 1967–2008 were included. Prevalence of pre-eclampsia increased from 1967 to 1999 and decreased thereafter, with an overall prevalence of 3%. Rates increased more over time among younger than older women, resulting in a significantly lower excess risk of pre-eclampsia associated with high maternal age in later years. For example, relative risk (RR) of pre-eclampsia among primiparae aged 35 relative to <25 years changed from 2.4 [95% confidence interval (CI) 2.1, 2.7] in 1967–1976 to 1.2 [95% CI 1.1, 1.3] in 1999–2008. For recurrence risk, subsequent pregnancies to a mother were linked, with the mother being the unit of analysis. Recurrence risk of pre-eclampsia was high, particularly recurrence of preterm pre-eclampsia, with overall RR close to 50 of a second pregnancy with pre-eclampsia and preterm birth compared with women without pre-eclampsia in first pregnancies. Finally, stillbirth associated with pre- eclampsia decreased more than neonatal mortality over time, and in the last 5 years only a moderate excess risk of stillbirth and neonatal death was observed. Keywords: pre-eclampsia, time trend, maternal age, parity, recurrence. Introduction Pre-eclampsia is one of the leading complications of pregnancy associated with maternal and neonatal mor- bidity and mortality, intrauterine growth restriction, preterm delivery and admission to neonatal intensive care. 1–3 Its aetiology is largely unknown, but is thought to be multifactorial. Familial aggregation, both within sibships and over generations, suggests that genetic factors are important; 4–7 however, the mode of inherit- ance has not been described. Because of its unknown aetiology and its impact on maternal and fetal health, pre-eclampsia is subject to great research interest. 1–9 Since 1967, the Medical Birth Registry of Norway (MBRN) has collected data on all births in the country with a gestational age of 16 weeks or more, including pregnancy complications such as pre-eclampsia. 10 In the present study, we wanted to describe the epidemi- ology of pre-eclampsia in Norway as it appears based on data from the MBRN, including some risk factors, as well as perinatal mortality associated with pre- eclampsia. We also wanted to study time trends in the 190 doi: 10.1111/j.1365-3016.2012.01260.x © 2012 Blackwell Publishing Ltd Paediatric and Perinatal Epidemiology, 2012, 26, 190–198