ObjectiveTo test the hypothesis that a range of severity of placental vascular lesions underlies preeclampsia and that the likelihood of its clinical diagnosis increases with the extent and severity of uteroplacental vascular lesions.Methodsfour hundred sixty-five consecutive placentas of singleton, nonanomalous, live-born infants born before 32 weeks' gestation were examined prospectively, and uteroplacental vascular and related villous lesions were assigned a semiquantitative lesion score based on severity and extent of lesions. The summed scores of individual lesions yielded a total uteroplacental vascular lesion score, ranging from 0 to 21, that was correlated with the odds of a clinical diagnosis of preeclampsia, as well as with potential confounders, including maternal age, race, gestational age at delivery, and birth weight centile. Statistical analysis was performed using contingency tables, one-way analysis of variance, multiple logistic regression, and receiver operating characteristic curve.P< .05 was considered significant.ResultsA clinical diagnosis of preeclampsia was present in 78 of 465 (17%) cases. Logistic regression demonstrated that the total uteroplacental vascular lesion score related significantly to the diagnosis of preeclampsia (odds ratio 1.43, 95% confidence interval 1.31, 1.57) and this association was independent of gestational age at delivery and birth weight centile. Preeclampsia was diagnosed in 12 of 284 (4%) cases with no or minimal histologic evidence of placental vascular injury (total score less than 4). Conversely, the diagnosis was not made in 4% of cases despite the presence of extensive placental vascular injury (total score at least 14).ConclusionThe likelihood of clinical diagnosis of pre-eclampsia before 32 weeks increases with progressive impairment of the uteroplacental circulation. Histopathologic examination of the placenta can be used to confirm the diagnosis of preeclampsia.