ObjectiveTo determine the magnitude of the risk and the predictive clinical characteristics for development of preeclampsia when triploidy is diagnosed in the second trimester.MethodsA retrospective analysis of databases maintained by the cytogenetics laboratories at the University of Iown and University North Carolina was performed to identify all cases of triploidy. We examined the karyotype, maternal serum screening (particularly the hCG level), ultrasound results, and evidence of maternal hypertensive disease.ResultsSeventeen cases of triploidy were identified between 1987 and 1996. Preeclampsia or hypertension complicated six of these cases with onset between 15 and 22.5 weeks' gestation. In these six cases, the serum hCG level was extremely high. Serum results were available in seven cases in which preeclampsia did not develop, and the hCG levels were under 0.09 multiples of the median in five of the seven cases. In all six cases in which preeclampsia or hypertension developed, there was stenographic evidence of placentomegaly. Sonographic findings in 16 17 cases revealed fetal growth restriction, oligohydramnios, fetal anomalies, placentomegaly, or a combination of these.ConclusionIn our series of pregnancies complicated by triploidy, the risk of developing preeclampsia or hypertension in the second trimester was 35%. It appears that elevated serum hCG levels and placentomegaly are associated with a higher risk of preeclampsia but low hCG levels are not. This information is important in counseling patients who are hesitant to terminate a pregnancy purely for a fetal abnormality, even if the anomaly is lethal.