Summary. Thirty‐one fetuses with growth retardation were studied by Doppler estimation of the cardiac output from each side of the fetal heart. Asymmetrical growth retardation was diagnosed in 16 fetuses by a head to abdominal circumference ratio above the 95th centile. In the 15 fetuses with symmetrical growth retardation, the distribution of cardiac output was normal. The mean and maximum velocity of blood flow in the pulmonary artery and aorta were similar to values in normal fetuses, and there was a greater calculated output from the right heart than from the left. The right heart flow expressed as a percentage of the combined cardiac output was not statistically significantly different from that in normal fetuses. In contrast, all 16 fetuses with asymmetrical growth retardation had a higher mean and maximum velocity in the aorta than in the pulmonary artery. The calculated volume flow from each side of the heart showed a greater output from the left than the right heart in 15. The right heart flow expressed as a percentage of the combined cardiac output was statistically different from the value in normal fetuses. These findings are consistent with theories of the redistribution of fetal blood flow, where cerebral blood flow is preferentially ‘spared’.

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Blood flow velocity waveforms were recorded in four sites in the fetal circulation in a series of 271 normal and 71 complicated pregnancies. The sites were the umbilical artery, the uterine artery branches in the placental bed, and distal to the two arterial valves in the heart. The blood flow through the arterial valves was added to estimate combined cardiac output. Normal ranges for values in all sites were established in our own series, and were similar to other published results. Abnormality of the waveform in the umbilical artery proved the most useful predictor of perinatal morbidity. Reversal of the normal pattern of increasing diastolic flow in the umbilical artery with advancing gestation was an important prognostic finding in the pregnancies studied serially. The combined cardiac output did not fall until late in the course of fetal compromise, and low values were seen only with an abnormal umbilical artery tracing.

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