Risk factors and clinical manifestations of pre-eclampsia

Objective To study associations between established risk factors for pre-eclampsia and different clinical manifestations of the disease. Design A population-based, nested case-control study. Setting Information from 12,804 consecutive deliveries that took place over three years at a birth clinic, which alone serves a population of nearly 240,000 in Rogaland county, Norway. Subjects Cases of pre-eclampsia (n = 323) and healthy controls (n = 650) were selected. Pre-eclampsia was defined as increase in diastolic blood pressure (greater than or equal to 25 mmHg to greater than or equal to 90 mmHg) and proteinuria (greater than or equal to 1+ by dipstick testing) after 20 weeks of pregnancy. Main study measures Parity, previous pre-eclampsia, blood pressure, maternal weight, and maternal smoking were included as study variables. Women with pre-eclampsia were grouped according to clinical manifestations of the disease (i.e. severity [mild, moderate or severe]) and time of onset (early or late gestation). Associations with the study factors were estimated as relative risks (odds ratio, OR). Results Both nulliparity and hypertension increased pre-eclampsia risk, with no clear preference for any clinical subtype. High maternal weight was related to a higher risk of mild and moderate, but not severe, pre-eclampsia. Previous pre-eclampsia strongly increased the risk for pre-eclampsia in the current pregnancy, and the risk of early onset disease was especially high (OR 42.4; 95% CI 11.9-151.6). Overall, smoking was associated with a reduced risk for pre-eclampsia (OR 0.6; 95% CI 0.4-0.9). However, no effect of smoking was observed in the early onset disease group and among women with repeated pre-eclampsia. Conclusion Nulliparity and hypertension increased the risk for each subgroup of pre-eclampsia, but high maternal weight, previous pre-eclampsia and smoking were not consistently associated with each clinical subtype. This observation may suggest that heterogeneous clinical manifestations of pre-eclampsia may be preceded by different pathological mechanisms.