Ultrasonographic fetal cardiac measurement in isoimmunized pregnancies

To investigate the predictive value of the ultrasonographically measured fetal biventricular outer dimension (BVOD) in diastole in detecting neonatal anemia in pregnancies complicated by isoimmunization.

The records of all patients evaluated for isoimmunization in pregnancy from January 1992 to December 1994 were reviewed retrospectively. The fetal BVOD had been measured with real-time-directed M-mode fetal echocardiography. The BVOD measurement was plotted on a nomogram (with reference to biparietal diameter) and a percentile value determined graphically from the nomogram. Neonatal outcome was obtained prospectively and by chart review.

Sixty-three singleton fetuses from the study period who met entry criteria were identified. Anti-D sensitization represented 66% of cases of isoimmunization. Twenty (32%) fetuses required subsequent neonatal transfusion, and 43 (68%) did not. Seventeen fetuses (27%) had BVOD measurements greater than the 95th percentile, and 10 (59%) required subsequent transfusion. Infants in this group also had significantly lower hematocrits at birth (37.7 +/- 13.0% vs. 46.6 +/- 9.0%) and prolonged neonatal intensive care unit stay (10.7 +/- 10.0 vs. 4.7 +/- 3.6 days), respectively, when compared to patients with a BVOD measurement less than the 95th percentile. A BVOD 95th percentile threshold had a sensitivity, specificity and positive predictive value of 50%, 84% and 59%, respectively, in predicting the need for neonatal transfusion.

In patients with isoimmunization, a BVOD measurement in the 95th percentile or greater was associated with a relatively high likelihood of neonatal anemia and transfusion. Although the measurement is not sufficiently sensitive to be used as a single parameter in predicting neonatal compromise in these patients, it can be a useful, noninvasive adjunct to the management of isoimmunized pregnancies.