Central arterial hemodynamics in small‐for‐gestational‐age fetuses before and during maternal hyperoxygenation: a Doppler velocimetric study with particular attention to the aortic isthmus

Abstract

Hemodynamic changes indicating a normalization of fetal blood flow redistribution during maternal oxygen administration have been suggested to be of positive prognostic value in growth-restricted fetuses. The aortic isthmus has been suggested as a site for early detection of blood flow redistribution as well as for verification of a response to maternal hyperoxygenation. The present study was performed to investigate whether this concept could be confirmed in a study involving fetuses assumed to have only a moderate disturbance in fetoplacental hemodynamics.Twenty-five singleton fetuses with an estimated weight less than -2 SD below the gestational age-related mean and without any malformation or chromosomal aberration were studied between 27 and 38 (median 34) weeks of gestation.Velocity waveforms from the mitral valve, aortic valve, middle cerebral artery, aortic isthmus and umbilical artery were recorded before and during maternal breathing of 100% oxygen.Nine fetuses demonstrated absent or reversed end-diastolic velocity (ARED) in the aortic isthmus while forward flow was present in the umbilical artery. The cerebral artery pulsatility index (PI) increased with oxygen administration and there was a decrease in the aortic isthmus PI. Variables obtained from the other recording sites did not change with maternal hyperoxygenation.ARED in the aortic isthmus appears to be an early sign of blood flow redistribution in this group of fetuses. Maternal oxygenation results in velocity waveform changes that suggest an increase of cerebral vascular resistance and a redistribution of blood from the brain to the vascular beds supplied by the descending aorta. The aortic isthmus is a suitable site to verify this response.