title: Risk factors for recurrence of hypertensive disorders of pregnancy, a population-based cohort study.
abstract: BACKGROUND
  Hypertensive disorders of pregnancy (HDP) tend to recur from one pregnancy to the next. The aims of the study were to assess the recurrence risk according to type of HDP defined by gestational age at birth and to examine whether recurrence is associated with the following additional risk factors for HDP: maternal age, smoking, inter-delivery interval, diabetes, body mass index, and fetal growth restriction, and to assess temporal trends in these associations.
  
  
  METHODS
  All women with two singleton births in the Medical Birth Registry of Norway 1967-2012 (n = 742 980) were included in this population-based cohort study. Logistic regression was used to calculate odds ratios for the risk of recurrent HDP according to type of HDP.
  
  
  RESULTS
  The highest odds ratio of recurrence was observed for the same type of HDP based on gestational age at delivery. After gestational hypertension and term preeclampsia, the risk for the same type to recur increased 10-fold, whereas after late and early preterm preeclampsia, the risk increased 27- and 97-fold, respectively. The recurrence of early preterm preeclampsia was less influenced by additional risk factors compared with term HDP. Recurrence of early preterm HDP was significantly lower from 1993 onwards.
  
  
  CONCLUSIONS
  Recurrent HDP tended to be of the same type as the previous HDP. Risk of recurrence associated with additional risk factors was observed particularly after term. The odds ratio of recurrence of early preterm HDP was significantly lower from 1993 onwards.
authors.affiliation: Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Cathrine
authors.identifier: http://orcid.org/0000-0002-4331-1250
authors.initials: C
authors.lastname: Ebbing
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Svein
authors.identifier: http://orcid.org/0000-0002-5789-2922
authors.initials: S
authors.lastname: Rasmussen
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.|Medical Birth Registry of Norway, Norwegian Institute of Public Health, Bergen, Norway.
authors.forename: Rolv
authors.identifier: http://orcid.org/0000-0002-6126-8655
authors.initials: R
authors.lastname: Skjaerven
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.|Medical Birth Registry of Norway, Norwegian Institute of Public Health, Bergen, Norway.
authors.forename: Lorentz M
authors.initials: LM
authors.lastname: Irgens
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D046110:Hypertension, Pregnancy-Induced / Q000453:epidemiology*; D008423:Maternal Age; D009664:Norway / Q000453:epidemiology; D010298:Parity; D011247:Pregnancy; D011254:Pregnancy in Diabetics / Q000453:epidemiology; D018566:Pregnancy, High-Risk; D012008:Recurrence; D012307:Risk Factors; D055815:Young Adult
keywords: High-risk pregnancy; gestational hypertension; hypertensive disorders of pregnancy; population study; preeclampsia; preterm birth; recurrence