title: Risk of early or severe pre-eclampsia related to pre-existing conditions.
abstract: BACKGROUND
  Preeclampsia (PE), especially severe or early PE, is a leading cause of morbidity and mortality among mothers and infants. We estimated the population attributable fractions of severe or early PE associated with pre-existing conditions among nulliparous and multiparous women.
  
  
  METHODS
  Among 70 924 women in the Danish National Birth Cohort, we used hospital discharge data to identify 2117 cases of PE, of which 449 were early (<37 weeks), 426 were severe (clinically diagnosed) and 228 were both early and severe. Prospective interview data were supplemented with hospital registry data to identify women with pre-existing conditions. Generalized estimating equations were utilized to estimate adjusted relative risks, and population attributable fractions were calculated with 95% CI.
  
  
  RESULTS
  Pre-existing hypertension, diabetes, obesity or multiple gestation were associated with 22.3% (19.8-24.9) of all PE cases among nulliparous women. These conditions, or a prior preeclamptic pregnancy, were associated with 52.2% (46.4-57.9) of PE among multiparous women. Early PE was preceded by these pre-existing conditions among 34% (28.3-40.0) of affected nulliparous women and among 50% (37.5-63.4) of multiparous women. The fraction of severe PE associated with these conditions was 23% among nulliparas and 59% among multiparas. Being obese or overweight was associated with 15-17% of the population risk of early PE among nulliparous and multiparous women.
  
  
  CONCLUSIONS
  Pre-existing maternal and obstetric conditions are associated with a high proportion of severe or early cases of PE. Obesity and overweight contributed independently to the risk of pre-term PE, a finding with potentially profound public health implications.
authors.affiliation: Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA 15261, USA. jmcst43@pitt.edu
authors.forename: Janet M
authors.initials: JM
authors.lastname: Catov
authors.forename: Roberta B
authors.initials: RB
authors.lastname: Ness
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Kip
authors.forename: Jorn
authors.initials: J
authors.lastname: Olsen
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications; D007231:Infant, Newborn; D009765:Obesity / Q000150:complications; D011225:Pre-Eclampsia / Q000209:etiology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors