965 Accuracy of middle cerebral artery doppler ultrasound for fetal anemia prior to 24 weeks gestation

Abstract

Fetal middle cerebral artery (MCA) peak systolic velocity of Doppler ultrasound varies with gestational age, and it is unclear if established reference ranges are applicable to pregnancies less than 24 weeks. We aimed to estimate the positive predictive value and false positive rate of MCA Doppler ultrasound for assessment of fetal anemia at gestational ages less than 24 weeks. A retrospective cohort study was performed in a single healthcare system over a 10-year period. All fetuses at risk of alloimmunization less than 24 weeks gestation who had MCA Doppler ultrasounds were identified. Non-immune causes of fetal anemia were excluded. Peak MCA systolic velocity > 1.5 multiples of the median (MoM) were considered positive and periumbilical blood sampling was considered. Pregnancy and neonatal outcomes were reviewed for all patients. The positive predictive value of MCA Doppler peak systolic velocity for fetal anemia prior to 24 weeks was estimated with 95% confidence intervals based on the binomial exact method. 126 pregnancies at risk for fetal anemia due to maternal alloimmunization had MCA Doppler ultrasound assessments prior to 24 weeks gestation. Of these, eleven had MCA peak systolic velocity > 1.5 MoM. Seven of the eleven were confirmed to have fetal anemia on percutaneous umbilical sampling while four were false positives, corresponding to a positive predictive value of 7/11 (64%, 95% CI 31%, 89%) and a false positive rate of 4/11 (36%, 95% CI 11%, 69%). MCA Doppler assessment performed at less than 24 weeks gestation had a positive predictive value of 64% for identification of fetal anemia, suggesting that 1 in 3 are false positives. This must be taken into account when considering percutaneous umbilical sampling in patients were positive fetal MCA Dopplers before 24 weeks.