Fetal haemodynamic changes in fetuses during fetal development evaluated by arterial pressure pulse and blood flow velocity waveforms

Objective To study the relation between diameter pulse (pressure pulse) and flow velocity waveforms in the fetal descending aorta in fetuses with intr auterine growth retardation and acceleration Design Blood flow through a tubular system can be expressed by the ratio of blood pressure to vascular resistance. Doppler ultrasound and a phase lock ed loop echo tracking system coupled to a B-mode ultrasonic imager (central frequency 3.5 MHz) were used to assess downstream resistance and change in blood pressure, respectively Setting Tertiary referral unit in a teaching hospital Participants Serial study between 21 and 40 weeks of 22 women with normally grown fetuses at intervals of four weeks; 25 women with small for gestatio nal age fetuses with uteroplacental insufficiency thigh umbilical artery pu lsatility index); and six women with large for gestational age fetuses. Main outcome measures We measured the maximum systolic and minimum diastoli c diameter of the fetal descending aorta (the pulse amplitude) and then cal culated the pulsatile waveform time integral above the least diastolic diam eter (pulsatile area) and total waveform time integral (perfusion area). Results Normal fetal growth was associated with an increase in systolic and diastolic diameters in the fetal descending aorta with advancing gestation al age. Pulse amplitude, pulsatile and perfusion areas increased with gesta tional age. The increased pulse amplitude and increased pulsatile area in a ssociation with a decrease of the pulsatility index in the descending aorta during the second trimester suggested that purse pressure and stroke volum e were increased. In the group with intrauterine growth retardation, systol ic and diastolic diameters of the descending aorta and perfusion area were within the normal range. Moreover, there was an increase in the diastolic d iameter per unit fetal weight and a decrease in the pulsatile area. In the large for gestational age fetuses, there was an increase in the pulse ampli tude and pulsatile area. Conclusion These findings suggest that in growth restricted fetuses there i s an increase in diastolic pressure and a reduction in stroke volume, while in large for gestational age fetuses there is an increase in the pulse pre ssure and stroke volume. It is possible that measurement of pressure pulse waveform in relation to Doppler velocity waveform may be used to infer chan ges of blood flow.