Model-based estimation of the hemodynamic status of the growth-restricted fetus

Abstract

Intrauterine growth-restriction in fetuses results from abnormal placentation that leads to placental insufficiency and reduced fetal oxygenation. The assessment of fetal condition in-utero is based on Doppler ultrasound. Increased pulsatility in the Doppler waveforms is usually attributed to increase in the placental resistance to blood flow, but this assumption cannot be validated in-utero.

In this study, we used mathematical models of the human circulation to form a model of the fetal cardiovascular system. The model was designed to allow evaluation of different parameters of the fetal circulation on the shape of Doppler waveforms. The model simulated flow waveforms in the fetal blood vessels in which Doppler measurements are taken. Model predictions were compared to published data and were found to be similar in both normal and IUGR fetuses. Our results indicated that other parameters of the fetal circulation, rather than placental resistance, may act as the major determinants of the Doppler velocity waveforms. These parameters are the resistance of the atrio-ventricle valves, cardiac contractility and venous resistance. These pathologies may be secondary to the increased vascular resistance. The model presented here may assist clinicians in evaluating fetal hemodynamics and help in clinical decisions such as the time of labor in growth restricted fetuses.