Human fetal foramen ovale flow velocity waveforms relative to behavioral states in normal term pregnancy

Neurodevelopment after fetal growth restriction

Fetal growth restriction (FGR) can emerge as a complication of placental dysfunction and increases the risk for neurodevelopmental delay. Marked elevations of umbilical artery (UA) Doppler resistance that set the stage for cardiovascular and biophysical deterioration with subsequent preterm birth characterize early-onset FGR. Minimal, or absent UA Doppler abnormalities and isolated cerebral Doppler changes with subtle deterioration and a high risk for unanticipated term stillbirth are characteristic for late-onset FGR. Nutritional deficiency manifested in lagging head growth is the most powerful predictor of developmental delay in all forms of FGR. Extremes of blood flow resistance and cardiovascular deterioration, prematurity and intracranial hemorrhage increase the risks for psychomotor delay and cerebral palsy. In late-onset FGR, regional cerebral vascular redistribution correlates with abnormal behavioral domains. Irrespective of the phenotype of FGR, prenatal tests that provide precise and independent stratification of risks for adverse neurodevelopment have yet to be determined.

Diagnostic value of an ROC curve of the size of the antepartum foramen ovale in the prediction of puerperal atrial septal defect

The aim of this study was to determine the diagnostic value of an ROC curve of the antepartum foramen ovale (AFO) size and the ratio of FO size to aorta (AO) size (FO/AO) for the prediction of puerperal atrial septal defect in different gestational weeks (DGWs). A total of 958 cases were divided into five groups according to number of gestational weeks. Comparisons of FO size, AO size and FO/AO were determined by variance analysis. The correlations between FO size, AO size and gestational age were determined using regression analysis and comparisons between atrial septal defect (ASD) diagnosed in DGWs and normal cardiac FO size and FO/AO were analyzed by t-test. ROC curve analysis was used for FO size and FO/AO to predict the demarcation point of puerperal ASD (pASD). The differences between FO size and AO size in the five groups at DGWs were statistically significant (P=0.000). The sizes of FO and AO increased with gestational age. The differences among pASD, normal cardiac FO size and FO/AO were statistically significant (P=0.000). FO size in the five DGW groups (18–22, 23–26, 27–30, 31–34 and 35–40 weeks) was able to predict the demarcation points of pASD, which were 5.02, 5.15, 6.55, 8.55 and 7.90 mm, respectively. The prediction of pASD with AFO size and FO/AO was accurate and may provide reliable reference values in the clinic.

Neurodevelopment following fetal growth restriction and its relationship with antepartum parameters of placental dysfunction

Placental dysfunction leading to fetal growth restriction (FGR) is an important risk factor for neurodevelopmental delay. Recent observations clarify that FGR evolves prenatally from a preclinical phase of abnormal nutrient and endocrine milieu to a clinical phase that differs in characteristics in preterm and term pregnancies. Relating childhood neurodevelopment to these prenatal characteristics offers potential advantages in identifying mechanisms and timing of critical insults. Based on available studies, lagging head circumference, overall degree of FGR, gestational age, and umbilical artery (UA), aortic and cerebral Doppler parameters are the independent prenatal determinants of infant and childhood neurodevelopment. While head circumference is important independent of gestational age, overall growth delay has the greatest impact in early onset FGR. Gestational age has an overriding negative effect on neurodevelopment until 32-34 weeks' gestation. Accordingly, the importance of Doppler status is demonstrated from 27 weeks onward and is greatest when there is reversed end-diastolic velocity in the UA or aorta. While these findings predominate in early-onset FGR, cerebral vascular impedance changes become important in late onset FGR. Abnormal motor and neurological delay occur in preterm FGR, while cognitive effects and abnormalities that can be related to specific brain areas increase in frequency as gestation advances, suggesting different pathophysiology and evolving vulnerability of the fetal brain. Observational and management studies do not suggest that fetal deterioration has an independent impact on neurodevelopment in early-onset FGR. In late-onset FGR further research needs to establish benefits of perinatal intervention, as the pattern of vulnerability and effects of fetal deterioration appear to differ in the third trimester.

The importance of venous Doppler velocimetry for evaluation of intrauterine growth restriction

The management of growth-restricted fetuses requires accurate diagnosis to optimize the timing of delivery. Doppler velocimetry is the only noninvasive method for assessing the fetoplacental hemodynamic status. This review will give a critical overview of the current knowledge on fetal venous blood flow in pregnancies complicated by in-trauterine growth-restricted fetuses. Adaptation of the circulation in intrauterine growth-restricted fetuses is described. Normal and abnormal venous Doppler waveforms are presented. Correlations of abnormal waveforms with the presence of acidemia and perinatal outcomes are emphasized. Limitations of venous Doppler velocimetry for optimizing the time for delivery and the perinatal outcome are also presented.

The ductus arteriosus

The ductus arteriosus is a large vessel which connects the pulmonary trunk with the aorta. During fetal life it serves together with the foramen ovale as a shunt at cardiac level. Due to a complex regulatory mechanism it is capable of maintaining patency during fetal life and of rapid closure after birth. However, in premature neonates ductal patency frequently persists, an occurrence which may even be favourable in some situations. Recent investigations on the ductus arteriosus have provided new information about the regulatory mechanisms involved with its function. Initially, most studies on the fetal ductus arteriosus were conducted in animals. With the introduction of the combined use of two dimensional real-time and Doppler ultrasound systems the opportunity became available to study blood flow within the ductus arteriosus in the human fetus and neonate in a noninvasive manner. The increasing use in obstetric care of cyclo-oxygenase inhibitors for tocolysis and for prevention of the development of pregnancy induced hypertension and pre-eclampsia justifies the re-evaluation of the potential adverse effects of these drugs on the ductus arteriosus.

The ductus venosus

The ductus venosus is a blood vessel functioning exclusively in the fetal circulation. According to many reports it was described for the first time by Giulio Cesare Arantius (Bologna 1530–1589) in his bookDe humano foetu libellus(1563) and it is often referred to as the ductus Arantii. Thorough research, however, has made it clear that Andreas Vesalius described this vessel in 1561 in his bookExamen observationium Falloppii, which was published three years later. Moreover, it has been pointed out that the first and second editions of Arantius’s book did not contain a description of the ductus venosus but that this appeared in the 1571 edition.

Umbilical venous volume flow and fetal behavioral states in the normally developing fetus

OBJECTIVE

To determine the relationship between umbilical venous (UV) volume flow and fetal behavioral states 1F (quiet sleep) and 2F (active sleep) in normal pregnancies at 36-40 weeks of gestation.

METHODS

Fetal behavioral states were established in 17 normal pregnancies by means of combined assessment of fetal heart rate patterns (FHRP), and fetal eye and body movements. UV vessel area (mm(2)) as obtained by tracing the inner vessel area using Labview and Imaq Vision software and UV time-averaged flow velocity (mm/s Doppler) were multiplied to calculate UV volume flow (mL/min) including flow/kg fetus. The pulsatility index (PI) in the umbilical artery was also determined. In each woman, all parameters were measured between three and five times in each behavioral state. Data are reported as mean +/- 1 SD and analyzed by paired t-test.

RESULTS

No statistically significant behavioral-state-related changes were observed for UV time-averaged velocity and UV volume flow, resulting in UV volume flow/kg fetus of 69.1 +/- 14.9 mL/min*kg at 1F and 71.6 +/- 12.1 mL/min*kg at 2F (not significant). A statistically significant increase (P = 0.02) was established for UV cross-sectional area (46.4 +/- 8.6 mm(2) vs. 49.0 +/- 10.1 mm(2)) and for fetal heart rate (FHR) from 134.2 +/- 10.3 bpm in 1F to 144.2 +/- 7 bpm in 2F. Umbilical artery PI was not significantly different between the two behavioral states.

CONCLUSIONS

On the basis of high venous vessel wall compliance, the significant increase in UV cross-sectional area during fetal behavioral state 2F may be determined by a rise in mean venous pressure. The significant rise in FHR may reflect increased fetal cardiac output during state 2F while the resistance at the hepato-ductal pathway remains relatively constant with the purpose of meeting raised energy demands during the active sleep state. This is further supported by the observed trend towards an increase in UV volume flow.

Cerebral hemodynamics and fetal behavioral states

OBJECTIVE

This study aimed to evaluate the hemodynamic patterns of the proximal (M1) and distal (M2) portions of the middle cerebral artery, during different fetal behavioral states.

DESIGN

The study included 20 normal singleton pregnancies at between 36 and 40 weeks of gestation. After identification of the fetal behavioral state (FBS), flow velocity evaluation was performed on the proximal and distal segments of the middle cerebral artery during 'quiescence' (FBS-1F) and 'activity' (FBS-2F).

RESULTS

A statistically significant decrease of pulsatility index, reflecting a decrease of impedance to flow values, was identified in both segments of the middle cerebral artery (MCA) during 'activity', with a more marked decrease in the MCA-M2 than in MCA-M1 (M1, P = 0.0028; M2, P = 0.00000085). The mean fetal heart rate during 'quiescence' was significantly lower than during 'activity' (P = 0.0047). However, there was no significant correlation between the pulsatility index of both segments of the middle cerebral artery and the fetal heart rate during different fetal behavioral states.

CONCLUSIONS

The results of this study provide evidence of the influence of different fetal behavioral states on fetal cerebral hemodynamic patterns. We believe it is better to sample the proximal segment in clinical practice because it is less influenced by fetal behavioral state. This information should be considered when evaluating fetal cerebral hemodynamics.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.

Fetal atrioventricular, venous, and arterial flow velocity waveforms in the small for gestational age fetus

Arterial, venous, and intracardiac Doppler flow velocity waveforms were studied in 50 women with a small for gestational age (SGA) fetus according to a cross-sectional study design. No Doppler signals could be obtained in five women for technical reasons. The remaining 45 women were compared with normal control subjects matched for gestational age and maternal parity. The 45 SGA fetuses were divided into birth weight below the 5th centile for gestational age (group I, n = 35) and birth weight between the 5th and 10th centile for gestational age (group II, n = 10). A significant difference in baseline characteristics was found between both SGA subsets and normal controls. In SGA I fetuses, the pulsatility index in the umbilical artery and descending aorta was significantly higher, but lower in the middle cerebral artery when compared with normal controls. At the atrioventricular and venous level (umbilical vein, ductus venosus, and inferior vena cava) reduced time-averaged velocities were established. PIV in the ductus venosus and IVC showed a significant increase. Within the same SGA subset, no relationship could be established between arterial downstream impedance and 1) atrioventricular flow velocities and 2) pulsatility index in the ductus venosus and inferior vena cava. Also, no relationship existed between flow velocity waveforms and pregnancy-induced hypertension and admission to the neonatal intensive care unit. Umbilical venous pulsations and absent/reverse flow in the umbilical artery were associated with a high intrauterine mortality rate and low birth weights. In SGA II fetuses, the pulsatility index in the umbilical artery and descending aorta was significantly higher than in normal controls. It can be concluded that fetuses with a birth weight below the 5th centile demonstrate marked changes in arterial, atrioventricular, and venous flow velocity waveforms. Atrioventricular and venous flow velocity waveforms change independently from arterial downstream impedance, suggesting that other factors, such as reduced volume flow and myocardial contraction force, may play a role in the observed changes.

Dependence of aortic pulse wave assessments on behavioural state in normal term fetus

To investigate any influence of behavioural states on the pulse waves in the descending aorta, 21 human fetuses were studied in utero in uncomplicated gestation at the age of 36-41 weeks. The fetal behavioural states were identified using two real-time scanners and one cardiotocograph. The aortic waveform data and pulse wave velocity (PWV) were recorded by means of two double phase-locking echo-trackers. The PWV of the fetal aorta was significantly lower in fetal behavioural state (FBS) 2F than in FBS 1F, when the fetus was apnoeic, and was also reduced in both states during fetal breathing. The calculated pulse pressure showed the same trend as the PWV. The fetal aortic end diastolic diameter and the pulse amplitude did not alter, when the two states changed. Our data suggest that the central haemodynamics in term fetuses are independently influenced by their behavioural state as well as by fetal breathing. The study of pulse waves in the fetal aorta should preferably be performed during apnoea in state 1F, when neither gross body movements nor breathing movements disturb the recording.

Assessment of flow events at the ductus venosus-inferior vena cava junction and at the foramen ovale in fetal sheep by use of multimodal ultrasound

BACKGROUND

Previous techniques for the study of the fetal circulation did not permit assessment of phasic events associated with the cardiac cycle. We used multimodal ultrasound techniques to examine flow events that occur in the major veins and across the foramen ovale in the circulation of the fetal lamb.

METHODS AND RESULTS

We studied eight fetal lambs instrumented with catheters in the superior and inferior venae cavae and a peripheral umbilical vein and performed ultrasound studies that included M-mode and two-dimensional imaging, pulsed and Doppler color flow ultrasound, and contrast echocardiography to evaluate flow in the ductus venosus, in both venae cavae, and through the foramen ovale. Two blood streams of different flow velocities were identified within the cephalic portion of the inferior vena cava. The stream that originated from the narrowed ductus venosus had a higher velocity than that from the caudal inferior vena cava (mean velocity, 57 +/- 13 versus 16 +/- 3 cm/s; P < .0002). Facilitated by the eustachian valve and the septum primum, the ductus venosus stream preferentially passed through the foramen ovale to the left atrium. This flow occurred during most of the cardiac cycle, except for 19.6 +/- 2.3% of the cycle when the foramen ovale was closed during atrial contraction. Superior vena cava flow passed almost exclusively into the right atrium and tricuspid valve; a small amount that was refluxed from the right atrium into the inferior vena cava subsequently passed through the foramen into the left atrium.

CONCLUSIONS

Visualization of fetal circulatory streaming at the venous sites by ultrasound techniques aids in understanding the function of the fetal circulation and may be helpful in detecting the human fetus that is hemodynamically compromised.

Fetal behaviour in normal and compromised fetuses. An overview

Fetal intrauterine behaviour is not a stable situation but a continuous alternation of states characterized by significant changes in fetal motility, heart rate, hemodynamics, metabolism and response to stimulation. Associations between fetal heart rate patterns and movements occur from 26-28 weeks of gestation onwards. As fetuses grow older these variables become gradually more related temporally and clustered in behavioural states similar to those present in newborns. This article describes the technique of recording and analyzing fetal behaviour, its development in normal pregnancy and its influence on different physiological parameters that are assessed in clinical practice. Furthermore the deviations from the norm occurring in compromised fetuses are described.

Assessment of fetal compromise by Doppler ultrasound investigation of the fetal circulation. Arterial, intracardiac, and venous blood flow velocity studies

BACKGROUND

Doppler studies of the fetal circulation in intrauterine growth retardation and hypoxia have demonstrated a compensatory redistribution of arterial blood flow with increased flow to the cerebrum and myocardium and decreased flow to the periphery. The aim of this study was to evaluate the significance of changes in fetal venous blood flow waveforms in high-risk pregnancies and to investigate the time relation between alterations in venous and arterial Doppler waveform indices in compromised fetuses.

METHODS AND RESULTS

The cross-sectional study consisted of 108 high-risk singleton pregnancies between 23 and 42 weeks' gestation without fetal chromosomal abnormalities or major malformations. Blood flow velocity waveforms were recorded from the umbilical arteries, descending thoracic aorta, middle cerebral artery, tricuspid and mitral ventricular inflow, ductus venosus, inferior vena cava, and the right hepatic vein. The mean velocity and pulsatility index were calculated for arterial vessels, the E/A ratio for atrioventricular blood flow, and peak forward velocities during ventricular systole and early diastole, the lowest forward velocity or peak reverse velocity during arterial contraction, and time-averaged maximum velocity for venous vessels. Two ratios for venous waveforms, one of which is the equivalent of the pulsatility index, were calculated. Fetal biophysical assessment was based on a computerized cardiotocogram and the biophysical profile score. The compromised group consisted of 37 fetuses delivered by cesarean section for an abnormal heart rate trace (n = 21) or severe preeclampsia (n = 9) or which died in utero (n = 7) within 10 days of their last Doppler investigation. This group showed significant alterations in arterial and venous flow velocity waveforms but not in atrioventricular inflow. Additionally, to find out whether venous Doppler investigation may help to detect a worsening of the situation in fetuses already showing arterial blood flow redistribution, we analyzed the data of these fetuses separately. The 41 fetuses that had an aorta/middle cerebral artery pulsatility index ratio > 95th percentile were divided into compromised and non-compromised groups according to their biophysical assessment and whether or not they developed fetal distress (cesarean section for abnormal heart rate trace or intrauterine death). The mean values for Doppler parameters of the compromised groups differed significantly from the noncompromised groups in all venous vessels, whereas differences on the arterial side were much less pronounced. Velocity ratios of venous waveforms were significantly higher, and absent or reverse flow in the ductus venosus with atrial contraction indicated a poor prognosis, with a perinatal mortality of 5 out of 8.

CONCLUSIONS

Fetal compromise is associated with significant alterations in the fetal arterial and venous circulation. Significant changes in venous Doppler waveforms develop due to increased afterload and perhaps myocardial failure in late deterioration after fetal arterial redistribution is established and seem to be closely related to abnormal biophysical assessment findings. Therefore, Doppler investigation of the fetal venous circulation may play an important role in monitoring the redistributing growth retarded fetus and thereby may help to determine the optimal time for delivery.

Behavioural state dependency of renal artery and descending aorta velocimetry and micturition in the normal term fetus

OBJECTIVE

To examine the behavioural state dependency of renal artery and descending aorta pulsatility index and hourly fetal urinary production rate (HFUPR) in the normal term fetus.

DESIGN

An observational study.

SUBJECTS

Twenty-three healthy women with a normal singleton pregnancy between 36 and 40 weeks gestation.

MAIN OUTCOME MEASURES

Renal artery and descending aorta pulsatility indices were established using pulsed Doppler ultrasound. HFUPR (ml) was estimated using real-time ultrasound. Fetal behavioural states 1F (quiet sleep) and 2F (active sleep) were determined from combined recordings of fetal heart rate, eye movements and body movements.

RESULTS

An inverse correlation between pulsatility index and fetal heart pattern was established for both the renal artery (r = 0.60; SD = 0.22; P = 0.0001) and the descending aorta (r = 0.73; SD = 0.16; P = 0.0001). The difference in mean pulsatility index between states 1F and 2F adjusted for fetal heart pattern was 0.09 (SD 0.23) for the renal artery (P = 0.02) and 0.26 (SD 0.19) for the descending aorta (P = 0.0001). Mean HFUPR was significantly higher (44.8%, P = 0.01) in state 1F (96 ml) compared with state 2F (54 ml). During the urinary filling phase, a poor correlation existed between renal artery pulsatility index and HFUPR (r = 0.04) and between descending aorta pulsatility index and HFUPR (r = 0.01).

CONCLUSIONS

In the normal term fetus renal artery and descending aorta pulsatility indices are reduced during fetal behavioural state 2F, suggesting reduced downstream impedance at the fetal trunk and in particular at renal level. This behavioural state is, however, also associated with reduced micturition. No correlation exists between renal artery and descending aorta pulsatility indices and fetal urinary output.

Doppler colour flow imaging of fetal intracerebral arteries relative to fetal behavioural states in normal pregnancy

In 14 normally developing term fetuses, the relationship between the blood flow velocity waveforms at cerebral arterial level (internal carotid artery, anterior, middle and posterior cerebral artery) and fetal behavioural states was studied using Doppler colour flow imaging. Behavioural state dependent changes in absolute flow velocities occurred in all vessels, except for the middle cerebral artery. These changes suggest preferential blood flow to the left heart resulting in increased flow to the cerebrum during fetal behavioural state 2F (active sleep) when compared with fetal behavioural state 1F (quiet sleep). The middle cerebral artery supplies the neocerebrum. This developing part of the cerebrum does not seem to take part in the regulation of fetal behaviour. In the internal carotid artery, an inverse relationship between peak systolic velocity and fetal heart rate could be established, which can be explained by a shorter rapid filling phase at raised fetal heart rate according to the Frank-Starling Law.

Inferior vena cava flow velocity waveforms relative to fetal behavioural states and sample site in normal term pregnancy

Reproducibility and behavioural state dependency of flow velocity waveforms from the proximal and distal part of the fetal inferior vena cava were studied in a total of 27 normal pregnancies at 36-39 weeks of gestation. Within patient coefficients of variation in fetal inferior vena cava waveform recording were markedly higher for the proximal part compared with the distal part. This is also reflected by lower reliability values as a measure of the relative proportion of within patient and between patient variance components. No statistically significant changes in flow velocity values could be detected at proximal and distal level of the fetal inferior vena cava relative to fetal behavioural states. A marked difference in flow velocity values was, however, observed between the two measuring sites with the highest velocities at proximal level. Since a considerable variation in fetal inferior vena cava flow recording was established, a possible behavioural state related modulation may have been obscured by these waveform variabilities.

Behavioural states and cardiovascular dynamics in the human fetus; an overview

Behavioural state dependent changes occur in the circulation of the normally developing human fetus at term. During fetal behavioural state 2F (active sleep), there seems to be preferential blood flow through the ductus venosus and foramen ovale into the left heart. Increased left ventricular output of well-oxygenated blood during fetal behavioural state 2F will be necessary to meet the raised energy demands both at cerebral and trunk level as demonstrated by reduced pulsatility index values in the descending aorta, renal artery and intracranial arteries during this behavioural state. The limited studies in IUGR suggest behavioural state independency in the descending aorta and internal carotid artery which may be attributed to the fetus being incapable of adjusting its circulation to the existing behavioural state in the presence of circulatory centralization.

Ductus venosus flow velocity waveforms in relation to fetal behavioural states

OBJECTIVES

To establish the reproducibility of flow velocity waveforms in the human ductus venosus and to assess the influence of fetal behavioural states on these waveforms in normal term fetuses.

DESIGN

Reproducibility of Doppler waveform recording and analysis was studied in 10 normal pregnancies. The relation between ductus venosus flow velocities and behavioural states was investigated in 19 other term fetuses. Time-averaged, peak systolic, peak diastolic velocity, peak systolic/diastolic ratio and period time were calculated in both cross sectional studies.

SETTING

Outpatient clinic, department of obstetrics (prenatal diagnosis section), Academic Hospital, Rotterdam--Dijkzigt.

SUBJECTS

Twenty-nine women with normal singleton pregnancies at 36 to 39 weeks of gestation, resulting in uncomplicated births of healthy infants.

RESULTS

Within-patient coefficients of variation, ductus venosus waveform recordings were approximately 8 to 10% except for the peak systolic/diastolic ratio (4.3%). A decrease of approximately 30% was established for peak systolic, peak diastolic velocity and time-averaged velocity during behavioural state 1F (quiet sleep) as compared with state 2F (active sleep).

CONCLUSIONS

Flow velocity waveform recording in the ductus venosus demonstrates acceptable reproducibility. Fetal behavioural state-dependent changes were observed, suggesting a redistribution of umbilical venous blood through the ductus venosus shunt during the quiet sleep state.

There are no rest-activity dependent changes in fetal ductus arteriosus flow velocity patterns at 27-29 weeks of gestation

Blood flow velocity waveforms recorded in the fetal ductus arteriosus were related to fetal heart rate pattern (FHRP) in 13 normal pregnancies at 27-29 weeks of gestation. Recording time was always 65 min or more. In three women no low fetal heart rate (FHRP-A) variability was present, in the remaining 10 women high fetal heart rate (FHRP-B) variability was established in 80% of the recording time. There was no statistically significant difference between FHRP-A and FHRP-B pattern for all ductal flow velocity parameters, indicating rest-activity state independency in late second and early third trimester pregnancy.

Urine production rate is related to behavioural states in the near term human fetus

OBJECTIVE

To investigate the relation between hourly fetal urine production rate (HFUPR) and behavioural states 1F and 2F (corresponding to quiet and active sleep, respectively) in normal near term fetuses.

DESIGN

An observational study.

SETTING

A clinic for antenatal care at a university hospital.

SUBJECTS

Nineteen healthy pregnant women examined at 37 to 40 weeks of gestation.

MAIN OUTCOME MEASURES

Fetal behavioural states (1F and 2F) were assessed by means of fetal heart rate patterns (FHR A and FHR B). Using real time ultrasonography, HFUPR (ml/h) was estimated during behavioural states 1F and 2F.

RESULTS

During behavioural state 1F, HFUPR was significantly higher than during state 2F (P < 0.01). HFUPR falls by 47% from 50.8 +/- 24.4 ml/h in state 1F to 25.7 +/- 15.0 ml/h in state 2F.

CONCLUSIONS

During active sleep (state 2F) hourly fetal urine production rate is considerably reduced as compared to quiet sleep (state 1F).

Behavioural states and Doppler velocimetry of the renal artery in the near term human fetus

Transition of fetal behavioural state 1F to 2F coincides with cardiovascular changes measured by Doppler velocimetry e.g. a decrease in pulsatility index (PI) in the internal carotid arteries and in the descending aorta, indicating redistribution of blood flow. Recently, we reported a considerable reduction in fetal urine production rate of 47% during fetal behavioural state 2F as compared to 1F. It was suggested that this reduction is caused by an increase in renal vascular resistance during 2F. Using Doppler ultrasound, flow velocity waveforms (FVW) of fetal renal arteries were recorded during behavioural states 1F and 2F. Fetal behavioural states 1F and 2F were assessed by recording fetal heart rate pattern, eye movements and body movements. The PI of the renal artery FVWs were calculated as an index of renal vascular resistance to blood flow. Fifteen healthy pregnant women between 36 and 40 weeks gestational age were studied and the relationship between fetal renal vascular resistance to blood flow and behavioural states was determined. We found that PI values in the renal arteries did not change relative to behavioural state 1F and 2F. These findings suggest that renal vascular resistance to blood flow is not appreciably different in 1F and 2F. This is in contrast with urine production rate which is almost reduced by half during 2F in the near term fetus.