Doppler assessment of the fetal venous system.

This article describes the achievements in Doppler measurements of the fetal venous circulation with emphasis on the clinical impact of these techniques. In rhesus isoimmunization, fetal venous flow assessment gives useful information on the fetal haematologic condition and on the impact of blood transfusion. In first trimester fetuses, Doppler evaluation of the ductus venosus and umbilical vein could attribute to the detection of cardiac defects and/or chromosomal abnormalities. The inferior vena cava flow velocity waveform could be studied in cases of fetal arrhythmias to be able to diagnose the type of fetal heart rhythm disturbances. One of the more important applications of venous Doppler assessment is its use in the evaluation of the intrauterine growth retarded fetus, who is suffering from placental insufficiency. Decrease of the late diastolic flow component in the ductus venosus waveform and the presence of umbilical venous pulsations are distinct alterations, which have been detected before cardiotocogram deterioration occurs. The clinical possibilities of venous Doppler measurements are limited, and the use of the techniques requires intensive training.

Transient increase in nuchal translucency thickness and reversed end-diastolic ductus venosus flow in a fetus with trisomy 18.

In a twin pregnancy discordant for trisomy 18, the affected fetus at 13 weeks' gestation had an increased nuchal translucency thickness and reversed end-diastolic ductus venosus flow. At 20 weeks' gestation there was no nuchal edema and Doppler study of the central venous vessels demonstrated normal waveforms. The findings support the hypothesis that one of the mechanisms in the development of increased nuchal translucency is temporary cardiac strain.

Fetal venous and arterial flow velocity wave forms between eight and twenty weeks of gestation.

Our purpose was to study the nature and gestational age dependency of fetal venous Doppler flow velocity wave forms and their relationship with fetal arterial wave forms in early pregnancy. Venous and arterial Doppler recordings were performed in 262 normal singleton pregnancies according to a cross-sectional study design at 8-20 wk of gestation. A statistically significant age-dependent increase is established for the umbilical vein, ductus venosus, and inferior vena cava time-averaged velocity. Umbilical venous pulsatile flow patterns are observed up to 15 wk of gestation. The pulsatility index for veins in all three venous vessels displays a gestational age-dependent reduction. No relation can be established between the pulsatility index for veins and the pulsatility index in the descending aorta and umbilical artery. This may be explained by the fact that the pulsatility index for veins reflects cardiac ventricular preload, whereas the pulsatility index in the arterial vessels reflects downstream impedance at fetal placental level.

Normal fetal pulmonary venous blood flow velocity.

Our objectives were to describe the normal pulmonary venous blood flow velocity waveform and to establish reference ranges for the second half of pregnancy in healthy human fetuses. A total of 123 women with uncomplicated pregnancies of between 20 and 40 weeks were examined, using a combined color-coded Doppler and two-dimensional real-time ultrasound system. Pulsed Doppler flow velocity waveforms of pulmonary venous drainage into the left atrium were obtained from a transverse cross section of the fetal chest at the level of the cardiac four-chamber view. All waveforms were obtained during fetal apnea. The success rate in obtaining the pulmonary venous waveform was 81%. The waveform displayed a biphasic forward flow profile with a systolic and diastolic component. Peak systolic, peak diastolic and time-averaged velocities demonstrated a gestational age-related rise, whereas the peak systolic/peak diastolic ratio showed a gestational age-related reduction. The nature of the fetal pulmonary venous flow velocity waveform pattern suggests positive pressure towards the left atrium throughout the cardiac cycle. We speculate that an increase in volume flow and the pulmonary venous pressure gradient play a role in the gestational age-related changes in pulmonary venous flow velocities.

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.

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.

Presence of pulsations and reproducibility of waveform recording in the umbilical and left portal vein in normal pregnancies.

Reproducibility and inter-observer variability of intra- and extra-abdominal umbilical venous flow velocity and left portal venous flow velocity as well as heart-synchronous waveform pulsations in these vessels were studied in 23 women at 34-38 weeks of normal pregnancy.Limited reproducibility, expressed by large intra-patient coefficients and limits of agreement between two observers, was established for all standardized recording sites. Pulsations, defined as negative venous deflections of at least 10% of the mean velocity, were demonstrated at all locations ranging from 19.6% of the measurements at the free-floating loop of the umbilical vein to 78.4% of the measurements at the left portal vein. The present study shows that the limited reproducibility of venous flow velocity waveforms should be taken into consideration, and that the presence of pulsations can be demonstrated in normal late pregnancy.

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.

Doppler flow velocity waveforms in late first- and early second-trimester fetuses: reproducibility of waveform recordings.

The objective of the study was to assess the reproducibility of Doppler flow measurements of the fetal umbilical vein and artery, descending and ascending aorta, mitral and tricuspid valve, pulmonary artery, inferior vena cava and ductus venosus in early pregnancy. In a cross-sectional study, Doppler measurements were obtained in a total of 54 women at 11-16 weeks of gestation, at 2-5 different vascular sites, on 3-5 different occasions, at 5-min time intervals. The total variance in the various flow velocity parameters was partitioned in a between-subject and within-subject component by analysis of variance, and, from these calculations, coefficients of variation in waveform recording were calculated. Flow velocity waveform recording was characterized by coefficients of variation in the range 2.2-5.7% except for the acceleration time (18.6-24.5%) and percentage reverse flow (8.8%). In conclusion, our data suggest that fetal flow velocity waveforms in early pregnancy demonstrate good reproducibility in the individual subject, while all parameters depict larger variabilities for between-subject values. Acceleration time turned out to be poorly reproducible. If a single flow velocity waveform measurement is used for the future evaluation of clinical conditions in early pregnancy, one has to consider that normal values will display a rather wide range.

Flow velocity waveforms in the ductus venosus, umbilical vein and inferior vena cava in normal human fetuses at 12-15 weeks of gestation.

The objective was to determine the normal Doppler flow velocity waveform patterns in the human fetal ductus venosus, inferior vena cava and umbilical vein correlated with fetal heart rate, and to examine their reproducibility and their inter-relationship at 12 to 15 weeks of gestation. Cross-sectional recordings of 45 normal pregnant women were collected for a data reference range transvaginally and transabdominally depending on fetal size and position. Maximum flow velocity waveforms were obtained from the ductus venosus, the intra-abdominal part of the umbilical vein and inferior vena cava. Time-averaged velocities were calculated in all three vessels together with peak systolic, peak diastolic and time-averaged velocities in the ductus venosus and inferior vena cava. Doppler recordings in 21 other patients displayed good reproducibility. Continuous forward flow in the umbilical vein was associated with pulsatile systolic and diastolic forward flow in the ductus venosus. Retrograde flow was present only in the inferior vena cava. Mean time-averaged velocity (SD) in the ductus venosus was 28.8 (6.1) cm/s, in the umbilical vein 9.7 (2.9) cm/s and in the inferior vena cava 10.9 (2.5) cm/s. No correlation could be established between waveform parameters and fetal heart rate. Combined transvaginal and transabdominal Doppler ultrasound allows reproducible blood flow velocity recordings at venous level in early pregnancy. Relatively high velocities were observed in the ductus venosus compared with the umbilical vein and inferior vena cava. Differences in flow velocities in the ductus venosus and inferior vena cava suggest that little or no mixing of blood occurs, a situation well described in sheep.

Changes in inferior vena cava blood flow velocity and diameter during breathing movements in the human fetus.

Breathing movements in the human fetus cause distinct changes in Doppler flow velocity measurements at arterial, venous and cardiac levels. In adults, breathing movements result in a momentary inspiratory collapse of the inferior vena cava vessel wall. The study objective was to quantify the inferior vena cava flow velocity modulation during fetal breathing movements and to evaluate possible inferior vena cava vessel diameter changes in normal third-trimester pregnancies. We studied 57 women after oral administration of dextrose (50 g). In 40 fetuses (n = 19, 27-32 weeks and n = 21, 36-39 weeks), fetal inferior vena cava waveforms were obtained during apnea and fetal breathing activity. In 30 fetuses (27-39 weeks) inferior vena cava vessel diameter changes were studied using the M-mode during apnea and breathing movements. Peak and time-averaged velocities of inferior vena cava flow velocity waveforms showed a gestational age-independent increase of 60-160% during breathing activity. A temporary inferior vena cava vessel wall collapse (range, 50-83%) was recorded, which was significantly different from vessel diameter changes during apnea (range, 11-19%). The marked increase of inferior vena cava flow velocities is due to a raised thoraco-abdominal pressure gradient, which may cause a reduction in vessel size and additional volume flow into the right atrium. The significance of the caval index for recognition of elevated right atrial pressure in abnormal human fetal development needs further investigation.

Normal Doppler flow velocity waveforms in the fetal ductus arteriosus in the first half of pregnancy.

Ductus arteriosus flow velocity patterns were studied in 298 women between 9 and 25 weeks of gestation using transvaginal or transabdominal Doppler ultrasound. Technically acceptable recordings were first obtained at 11 weeks resulting in 231 women for further analysis. Ductal waveforms show a significant change in shape from early pregnancy to mid-pregnancy, in that end-diastolic velocities are absent until 13 weeks, are present in 50% at 15 weeks and are present in all cases from 17 weeks. Regression analysis demonstrated a statistically significant linear increase with advancing gestational age for all flow velocity parameters except for the pulsatility index which remained stable during the entire study period.

Recognition of a fetal subdiaphragmatic venous vestibulum essential for fetal venous Doppler assessment.

Ultrasonic visualization of the human fetal subdiaphragmatic area demonstrated anatomical relationships, different from descriptions in the literature. Four human fetal postmortem specimens at 18, 26, 28, and 34 wk of gestation were examined to ascertain morphologic details of intra- and perihepatic vasculature. Drawings of these dissected preparations were compared with ultrasonic images from the same region. With both methods the presence of a venous vestibulum immediately proximate to the diaphragm could be demonstrated. The abdominal inferior vena cava ends in a funnel-like structure, which also contains the orifices of the hepatic veins, the ductus venosus, and a phrenic vein. A considerable variability in Doppler flow recordings could result from blood propelling out of these various vessels into the vestibulum. It is, therefore, suggested that information on blood-flow velocities in venous hepatic vessels should be obtained more distally in the separate vessels and not at the entrance into the right atrium.

Doppler assessment of the normal early fetal circulation.

Combined transvaginal and transabdominal Doppler ultrasound allows recording of fetal intra- and extracardiac flow velocity waveforms in late first- and early second- trimester pregnancies. At 10-12 weeks, end-diastolic flow velocities were always absent in the fetal descending aorta and umbilical artery, but were present in over half of the intracerebral artery waveforms. The pulsatility index in the three vessels decreased significantly with advancing gestational age, suggesting a reduction in fetal and umbilical placental vascular resistance. Peak velocities during atrial contraction (A-wave) were nearly twice as high as those during early diastolic filling (E-wave), reflecting low ventricular compliance. Continuous forward flow in the umbilical vein was associated with a pulsatile systolic and diastolic forward flow in the ductus venosus. Retrograde flow was only present in the inferior vena cava.

Normal fetal Doppler inferior vena cava, transtricuspid, and umbilical artery flow velocity waveforms between 11 and 16 weeks' gestation.

OBJECTIVES: Our objectives were to determine flow velocity waveform patterns in the fetal inferior vena cava and to relate these waveforms to transtricuspid and umbilical artery waveforms and fetal heart rate in early gestation. STUDY DESIGN: Doppler waveforms were recorded in 40 normal fetuses at 11 to 16 weeks of gestation. Only transvaginal scanning was carried out at 11 to 12 weeks and only transabdominal scanning was used at 15 to 16 weeks. RESULTS: The ratio of time velocity integrals of flow from the inferior vena cava during systole and early diastole, the percentage of reverse flow in this vessel, the pulsatility index from the umbilical artery, and the fetal heart rate were negatively correlated with gestational age. Peak E-wave and A-wave velocities and E/A ratios from the transtricuspid waveforms were positively correlated with gestational age. CONCLUSION: Early normal pregnancies are associated with remarkable changes in fetal flow velocity waveforms at both the cardiac and the extracardiac level.

Intracerebral, aortic, and umbilical artery flow velocity waveforms in the late-first-trimester fetus.

OBJECTIVES: Our objectives were to determine the success rate in obtaining flow velocity waveforms in the first-trimester fetal circulation and to establish possible preferential flow to the fetal cerebrum at this early stage of gestation. STUDY DESIGN: Flow velocity waveform recordings were made in the umbilical artery, fetal descending aorta, and fetal intracerebral arteries in 30 normal pregnancies between 11 and 13 weeks of gestation. RESULTS: Technically acceptable waveforms were obtained from the descending aorta in 15 fetuses, from the intracerebral circulation in 17 fetuses, and from the umbilical artery in all 30 fetuses. Absent end-diastolic velocities in the descending aorta and umbilical artery were associated with forward flow throughout the cardia cycle in intracerebral arteries. CONCLUSION: A relatively low cerebral vascular resistance in the late-first-trimester normal fetus is suggested.

Ductus venosus blood flow velocity waveforms in the human fetus--a Doppler study.

Successful human fetal ductus venosus flow velocity waveform recording was achieved cross sectionally in 48 out of 60 women at 19-22, 27-30 and 36-39 weeks of gestation. The ductus venosus shows a pulsatile flow pattern consisting of a systolic and diastolic forward component without a late diastolic reverse component as demonstrated in the inferior vena cava. Peak systolic velocities as high as 40-80 cm/s were observed. A statistically significant increase in time-averaged velocity, peak systolic and peak diastolic velocity with advancing gestational age was established.

Fetal and umbilical flow velocity waveforms between 10-16 weeks' gestation: a preliminary study.

Maximal flow velocity waveform recording was attempted in the umbilical artery, fetal descending aorta, and at the fetal intracerebral level using a cross-sectional study design in 77 normal singleton pregnancies between 10-16 weeks' gestation. At 10-12 weeks, end-diastolic flow velocities were always absent in the fetal descending aorta and umbilical artery, but were present in 58% of the intracerebral artery waveforms. The pulsatility index at all three levels decreased significantly with advancing gestational age, suggesting a reduction in fetal and umbilical placental vascular resistance during the late first and early second trimesters of normal pregnancy. Waveform changes were not related to fetal heart rate.

Fetal cardiac flow velocities in the late 1st trimester of pregnancy: a transvaginal Doppler study.

In 30 normal women with a singleton pregnancy, transvaginal Doppler ultrasound was used to record flow velocity at the fetal atrioventricular (AV) valve and outflow tract levels (ascending aorta and pulmonary artery) at 11 to 13 weeks of gestation. Technically acceptable flow velocity waveforms were recorded at the AV valve level in 19 fetuses and in the ascending aorta and pulmonary artery in 15 and 17 fetuses, respectively. Successful documentation of both transmitral and transtricuspid flow velocity waveforms was achieved in six fetuses only. Peak velocities during atrial contraction (A wave) were nearly twice as high as those during early diastolic filling (E wave), reflecting low ventricular compliance. Peak and time-averaged flow velocities in the outflow tract were lower than those observed in 2nd and 3rd trimester pregnancies with mean values of 32.1 +/- 5.4 (+/- SD) and 11.2 +/- 2.2 cm/s, respectively, in the ascending aorta and 29.6 +/- 5.1 and 10.8 +/- 2.1 cm/s in the pulmonary artery.