Blood flow and behavioural states in the human fetus

The objective of the present study was five-fold: The first objective was to establish in normal pregnancy a possible relationship between the flow velocity waveform in the fetal descending aorta and fetal behavioural state, in particular states 1F and 2F according to the classification of Nijhuis et al (1982). These two behavioural states were studied because of the high incidence of 1F (32%) and 2F (42%) at 38 weeks and the marked differences in fetal heart rate pattern, fetal eye movements and fetal body movements between these two behavioural states (Nijhuis et al, 1982). State 3F and 4F were excluded from the study because of the low incidence of these behavioural states, respectively 1% and 7% of the recording time (Nijhuis et a!, 1982). Moreover during behavioural state 4F the fetus moves continuously too vigorous to obtain reliable blood flow velocity waveforms. Blood flow velocity waveforms were recorded at 37-38 weeks of gestation, since only then welldefined behavioural states could be expected (Chapter 3.1). The characteristic blood flow velocity changes in the fetal descending aorta observed during intrauterine growth retardation (IUGR) prompted a similar behavioural state related study in this high risk group and represented our second objective, the results of which can be found in Chapter 3.2. Doppler flow measurements are increasingly performed during the early third trimester of pregnancy for the early detection and evaluation of intrauterine growth retardation. The results obtained at 37-38 weeks justified a repeat of this study during the early third trimester of pregnancy. At 27-28 weeks of gestation there already is a clear periodicity of state variables, but there is no proper synchronization in their cyclic appearance, thus allowing elucidation of the role of separate variables on possible flow velocity waveform changes in the fetal descending aorta. This was the third objective of our study; the data are presented in Chapter 3.3. Following the introduction of an ultrasound method for recording blood flow velocity waveforms in the fetal internal carotid artery (Wladimiroff et al, 1986), the fourth objective was to relate these waveforms to fetal behavioural states in normal pregnancy at 37-38 weeks of gestation. It was decided to also include the umbilical artery in the study, since flow velocity waveforms from this vessel are often documented with respect to the early detection of IUGR. From the results collected in this cross-sectional study on blood flow velocity waveforms in the internal carotid artery as well as the earlier observation that during the last four weeks of gestation the pulsatility index in this vessel displays a gradual decline (Wladimiroff et al, 1987b), it was decided to also perform the behavioural ·state related study in the fetal internal carotid artery in a longitudinal design between 36 and 41 weeks of gestation. This would provide an answer to the question as to the role of fetal behavioural states in the fore-mentioned reduction in PI during late pregnancy. The results from the cross-s~ctional study are presented in Chapter 4.1, the results from the longitudinal study can be found in Chapter 4.2. The fifth objective of our study was to elucidate the possible role of fetal behavioural states in fetal internal carotid artery and umbilical artery blood flow measurements during IUGR. We, therefore, first established the incidence and magnitude of flow velocity waveform changes in these two vessels in the presence of IUGR with particular emphasis on the PI umbilical artery /internal carotid artery ratio as a possible predictor of fetal growth retardation. Results are presented in Chapter 4.3. This was followed by a cross-sectional study at 37-38 weeks of gestation, during which blood flow velocity waveforms in both vessels in IUGR were documented during behavioural state 1F and 2F. The data from this part of the investigation can be found in Chapter 4.4.