Fetal transfusion of red blood cells for alloimmunization: validity of a published equation

Abstract

Objective: To validate the equation published in 1990 by Leduc et al. for red blood cell fetal transfusion where fetoplacental blood volume (VO) = 100 ml/kg, then improve its precision.

Methods: We reviewed 101 fetal transfusions among 32 patients. We analyzed risk factors for an inaccurate estimation with uni- and multivariate analysis. We compared the obtained Leduc formula with three other published equations.

Results: Fetal weight and gestational age were risk factors for an inaccurate estimation of the final Hct. Before 32 weeks the estimation of VO was 120 ml/kg instead of 100 ml/kg. All formulae overestimated the mean expected Hct value. However, expected Hct estimated by Leduc's formula is the nearest of the observed final Hct.

Conclusion: Leduc's equation seems to be accurate, but less so for the youngest fetuses. We propose an adapted formula VO according to gestational age and fetal weight estimation.