OBJECTIVETo assess the diagnostic accuracy of amniotic fluid Δ OD 450 values in the second and third trimesters of D-alloimmunized pregnancies.METHODSWe searched our database for singleton D-alloimmunized pregnancies with nonhydropic fetuses, where amniocentesis was performed within 4 days of first fetal blood sampling. Amniotic fluid Δ OD 450 values were plotted on an extrapolated Liley's chart. Sensitivity and specificity were calculated for two commonly used cutoff levels, Liley's zone 3 and the upper third of Liley's zone 2. Severe fetal anemia was defined as a hemoglobin concentration of more than 5 standard deviations below the normal mean for corresponding gestational age.RESULTSSeventy-nine pregnancies met our inclusion criteria. Overall accuracy of the extrapolated Liley's curve in predicting severe fetal anemia was 75% (95% confidence interval [CI] 64, 84) for zone 3 and 86% (95% CI 77, 93) when the upper third of zone 2 was included. Sensitivity of Δ OD 450 values in Liley's zone 3 or the upper third of Liley's zone 2 was 95% (95% CI 74, 100) before and 98% (95% CI 89, 100) after 27 weeks.CONCLUSIONLiley's extrapolated curve predicts severe fetal anemia with reasonable accuracy and high sensitivity.