Predictive value of elevated middle cerebral artery peak systolic velocity in cases of fetal anemia

Abstract

VELOCITY IN CASES OF FETAL ANEMIA KARIN FUCHS, STEPHEN CARR, Brown University, Obstetrics/Gynecology, Providence, Rhode Island OBJECTIVE: To determine if middle cerebral artery peak systolic velocities (MCA-PSV) measured in clinical practice at a teaching hospital accurately predicted the presence and severity of fetal anemia. STUDY DESIGN: Eighteen prenatal records from 2001 to 2004 were reviewed. MCA-PSV was measured within 24 hours of fetal blood sampling via percutaneous umbilical blood sampling (PUBS). For each case the date, gestational age, MCA-PSV and fetal hemoglobin (Hgb) was recorded. Published nomograms were used to determine the corresponding multipleof-the-median (MoM) for each MCA-PSV and fetal hemoglobin. Published parameters were used to define each MoM as either normal, or as mild, moderate, or severe anemia. The false positive rate (FPR = false positive / screen positive) of the MCA-PSV measurements was calculated by comparing the degree of fetal anemia predicted to that revealed at the time of PUBS. RESULTS: MCA-PSV predicted severe anemia in 11 fetuses, moderate in 5, mild in 1, and none in one. PUBS confirmed moderate or severe anemia in 6 of the 16 (38%) fetuses predicted to be moderately or severely anemic by MCAPSV. Ten of the 16 (63%) had mild or no anemia. Factors associated with more accurate prediction of fetal anemia included earlier gestational age at the time of MCA-PSV measurement (FPR 25% ! 28 weeks vs 75% O 28 weeks) and having MCA-PSV measured prior to 2004 (17% FPR vs 90% FPR in 2004). CONCLUSION: The false-positive rate in our clinical practice is higher than previously published and requires reconsideration of the predictive capacity of MCA-PSV. Research is ongoing to identify factors leading to the increased false-positive rate and to develop methods to ensure accuracy of MCA-PSV measurements.