Ultrasonographic monitoring of pregnancies complicated by red blood cell alloimmunization in a cohort with mild to moderate risk according to previous obstetric outcome.

AIM: To evaluate the detection rate of fetal anemia and pregnancy outcome as related to our policy of monitoring pregnancies with red blood cell alloimmunization.

METHODS: From August 1997 to July 2000 35 pregnant women with maternal red blood cell alloantibodies were monitored by ultrasonographic measurements of the fetal spleen perimeter and peak systolic Doppler flow velocities of the middle cerebral artery, by semiquantification of maternal antibody titers and by general ultrasonographic and clinical evaluation. According to previous obstetric outcome they all had mild to moderate risk of developing fetal anemia.

RESULTS: Eleven fetuses were anemic defined as a hemoglobin value < or = 2SD according to gestational age. A spleen perimeter > + 2SD and a middle cerebral artery peak systolic velocity > 95% prediction interval showed sensitivity and specificity of 64 and 92% and 45 and 100%, respectively. The area under receiver operating characteristic curves was 0.926 (95% CI 0.842-1.000; P < 0.001) for the spleen perimeter and 0.837 (95% CI 0.688-0.987; P < 0.01) for the middle cerebral artery peak systolic velocity. Cordocentesis was performed in one pregnancy only. None of the fetuses developed hydrops and all infants survived. Twelve women delivered before 37 weeks gestation. In 10 patients cesarean section was performed due to possible fetal anemia. Six of the 10 neonates had normal hemoglobin values.

CONCLUSIONS: The ultrasonographic parameters did not predict all cases of fetal anemia defined as a hemoglobin concentration < or = 2SD according to gestational age. The present policy of monitoring seemed to reduce the number of invasive tests but possibly increased the number of preterm and cesarean deliveries.