Risk of early or severe preeclampsia related to pre-existing conditions

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.