Myocardial contractility in the anemic human fetus

Severely anemic fetuses in Rh-isoimmunized pregnancies are often found to have hydrops and the etiology is debated. Fifteen fetal blood samplings were performed in nine fetuses for determination of the degree of anemia and of the acid-base balance. Waveform analysis was performed on the maximum blood velocity curve in the umbilical arteries and the ascending fetal aorta, obtained by means of a pulsed Doppler technique. The blood acceleration in the ascending aorta increased down to a hematocrit of 0.18 and a hemoglobin concentration of 65 g/l, which might constitute a cardiac response to the anemia aimed at maintaining the peripheral blood circulation. Below these levels there was a decrease in blood acceleration, which could be caused by impaired cardiac oxygenation. This relationship could be described as a six-power function (r = 0.87; p = 0.032). A second-power relationship was found between the umbilical artery pulsatility index and the blood acceleration in the fetal ascending aorta (r = 0.64; p = 0.0418), which suggests that the cardiac pump function can alter the blood velocity waveform in the umbilical arteries.