Digoxin-like immunoreactive substance in fetuses with and without cardiac pathology.

The concentration of digoxin-like immunoreactive substance was measured by immunoassay in umbilical venous blood from six normal and 19 fetuses with a variety of cardiac and noncardiac disorders. Fetal blood was obtained either by percutaneous umbilical blood sampling (n = 13) or at delivery (n = 12). Three women received digoxin for fetal indications. Healthy control fetuses had significantly less digoxin-like immunoreactive substance measured (mean concentration below the limit of the assay sensitivity) than was found in ill fetuses whose mothers received digoxin (p less than 0.005). However, the fetal concentrations of immunoreactive digoxin in fetuses with a cardiac abnormality were similar whether the mother had (0.93 +/- 0.4 ng/ml) or had not (1.27 +/- 0.4 ng/ml) received digoxin (p = 0.1452). Although there was a significant negative correlation between digoxin concentration and gestational age (R = -0.5079, p less than 0.01), the youngest fetuses examined were generally the sickest. The correlation with gestational age was not significant if the normal control fetuses were excluded. One fetus with a cardiac tachyarrhythmia was examined during and after transplacental therapy. There was no change. It is possible that previously measured "digoxin" in "treated" fetuses represents digoxin-like immunoreactive substance and that only small amounts of maternally administered digoxin actually reach the ill fetus. Our findings suggest that a randomized trial of maternal digitalization for the treatment of fetal supraventricular tachycardia is essential prior to its acceptance as effective therapy.