Objective: We conducted a large clinical trial to evaluate the effect of low-dose aspirin on the frequency of preeclampsia in nulliparous women. A secondary objective of the trial was to identify those clinical characteristics that might be predictive for the development of preeclampsia.
Study design: A total of 2947 healthy women with a single fetus were prospectively followed up from randomization at 13 to 27 weeks' gestation to the end of pregnancy. Of these, 1465 women were assigned to low-dose aspirin and 1482 to placebo. Baseline maternal blood pressure and demographic characteristics were examined for the prediction of preeclampsia.
Results: Preeclampsia developed in 156 women (5.3%). Four characteristics predicted the development of preeclampsia: in order of importance, systolic blood pressure at entry, prepregnancy obesity (weight as a percentage of desirable weight), number of previous abortions or miscarriages, and smoking history. Contrary to previous reports, black race was not a risk factor for preeclampsia. Systolic blood pressure was a better predictor of preeclampsia than either diastolic or mean arterial blood pressure. The greater the blood pressure or prepregnancy weight, the greater was the risk for preeclampsia. If the woman had never smoked or had never been previously pregnant, her risk was also higher than average. A multivariate logistic regression equation based on these four factors was able to define a tenth of the population at very high risk and another tenth at very low risk; the ratio of risk between these two groups was 12:1. The p value for each of the multivariate coefficients of the risk equation was systolic blood pressure (p < 0.001), prepregnancy weight (p < 0.01), smoking history (p < 0.01), and gravidity (p < 0.05). There were no statistically significant differences in the predictive values of these risk factors between women receiving low-dose aspirin or placebo.
Conclusions: These risk factors should be of value to practitioners counseling women regarding preeclampsia. Moreover, such risk factors should be considered in the design of future studies dealing with preeclampsia.