P. A. Stewart

Doppler ultrasound assessment of cerebral blood flow in the human fetus

Summary. A mechanical sector and linear array real‐time scanner combined with a pulsed Doppler system was used for recording the flow velocity waveform in the internal carotid artery, the lower thoracic part of the descending aorta and umbilical artery in the human fetus. A total of 42 fetuses in normal pregnancy and nine growth‐retarded fetuses between 26 and 41 weeks gestation was studied. In normal pregnancy the mean pulsatility index (PI) in the internal carotid artery varied between 1·5 and 1·6, in the descending aorta between 1·7 and 1·8 and in the umbilical artery between 0·7 and 1·3. In the growth‐retarded fetuses the PI was reduced in the internal carotid artery and raised in the descending aorta and umbilical artery, suggesting an increased peripheral vascular resistance in the fetal body and placenta and a compensatory reduction in peripheral vascular resistance in the fetal cerebrum, i.e. a brain‐sparing effect in the presence of fetal hypoxia.

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.

Efficacy of fetal echocardiography and yield by risk category

Objective To determine the efficacy and yield of tertiary center fetal echocardiography for different high-risk groups. Methods Between January 1, 1982, and January 1, 1994, scans for anomalies were performed on 3246 women at increased risk for congenital heart disease in their offspring. Gestational age was 16–25 weeks in 83%. Maternal and gestational age as well as prenatal and postnatal diagnosis were recorded, and follow-up was sought for all pregnancies. By comparing prenatal and postnatal diagnoses, sensitivity, specificity, and predictive values were estimated. Multiple logistic regression was applied to establish the relative yield within the high-risk group. Results Follow-up was available in 3223 cases (99%). In a separate validation study of 777 women for whom a second set of follow-up data was requested, no additional anomalies were revealed. In total, 20 of 47 cases of cardiac malformations were detected (sensitivity 43%). When taking into account cases that remained undetected because of unfavorable scanning conditions (ie, minute size of the anomaly, awkward fetal position, or severe maternal obesity), the sensitivity for congenital heart disease rose to 51%. Specificity and predictive values were high (above 95%). The relative yield across the high-risk group appeared to be high for parental congenital heart disease and maternal diabetes mellitus, whereas a previous infant or other relatives affected, maternal anti-epileptic drug use, maternal drug abuse, and other reasons for referral each had an estimated yield approximately equal to the prevalence of congenital heart disease in the general population (0.8%). Conclusion Fetal echocardiography for known increased risk appears to be moderately effective. Clear differences in yield are present across currently accepted risk categories.

Offsetting of the septal tricuspid leaflet in normal hearts and in hearts with Ebstein's anomaly: anatomic and echographic correlation

Apical displacement of the septal tricuspid valve leaflet is considered the most reliable criterion to diagnose Ebsteins anomaly. This feature is best assessed using 2-dimensional echocardiography. However, the anatomy in Ebsteins anomaly is highly variable; therefore, the problem arises as to how to distinguish between the abnormal displacement in borderline cases of Ebsteins disease and the lowered septal offsetting of the tricuspid valve in normal persons. To solve this problem the minimal and maximal differences in offsetting of the tricuspid and mitral valves have been studied, both anatomically and echocardiographically, in fetuses, infants, children and adults. In fetuses in the first trimester of pregnancy it was impossible to measure a difference in offsetting of the 2 atrioventricular valves. Thereafter, a gradual increase occurred with age. In normal hearts the most significant separation was usually recorded in anteriorly angulated 4-chamber views, whereas in hearts with Ebsteins anomaly maximal separation appeared to posteriorly angulated views. The anatomic and echographic measurements showed a constant relation. When the minimal distances in offsetting were measured, an overlap was found between cases with and those without Ebsteins anomaly. The maximal values, however, clearly discriminated between the 2 conditions. The critical difference in children was 15 mm, and in adults the discriminating value was 20 mm.

Flow velocity waveforms in the fetal inferior vena cava during the second half of normal pregnancy

Fetal inferior vena cava (IVC) flow velocity waveform recording was attempted at the entrance into the right atrium in 60 women at 19-22 weeks, 27-30 weeks and 36-39 weeks of gestation. Technically acceptable waveforms were collected in 48 women. A significant increase in time-averaged velocity and a significant decrease in percent reverse flow with advancing gestational age was established. A large standard deviation was observed for various IVC waveform parameters. From preliminary postmortem data it appeared that the inferior venous entrance into the right atrium represents a funnel-like structure composed of the inlet of the IVC, hepatic veins and ductus venosus. It is suggested that waveform recording at the scanning level employed in the present study provides information on gestational age-related changes in venous return to the right atrium rather than changes in the IVC itself. It is proposed that information on IVC flow velocity waveforms should be obtained more distal to the venous entrance into the right atrium.

Prenatal diagnosis by ultrasound in pregnancies at risk for autosomal recessive polycystic kidney disease

In 15 pregnancies at risk of the autosomal recessive type of polycystic kidney disease (ARPKD), there were six recurrences (40%), five of which were diagnosed prenatally between 17 and 26 weeks (mean, 22 weeks). In the remaining affected case, normal kidney size and echogenicity were still present at 30 weeks of gestation. Fetal kidney enlargement and increased echogenicity are the key ultrasonographic signs for the detection of ARPKD. Absent fetal bladder filling and oligohydramnios were only documented in two of the six affected pregnancies. The variability in onset, the intrafamilial variability and the limitations of excluding ARPKD by second trimester ultrasound have to be considered when counselling a couple at risk for this particular disorder.

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.

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.

Noninvasive management of isolated bilateral fetal hydrothorax

Fetal outcome was studied in eight cases of isolated bilateral fetal hydrothorax. All patients were referred because of polyhydramnios. Spontaneous resolution of pleural effusion was observed twice. No remarkable change in the degree of hydrothorax was demonstrated in the remaining six cases. All eight cases resulted in the birth of a live infant without other abnormalities. Postnatal intubation, which was carried out in all six fetuses with hydrothorax, was always followed by spontaneous respiration. Subsequent thoracocentesis resulted in the collection of 50 to 500 ml of serous fluid. Sustained intubation (7 days) was necessary in only two infants because of developing respiratory distress as a result of prematurity or recurrent pleural fluid accumulation. All eight infants were alive and well at the age of 1 month. Although in the present study noninvasive management of isolated fetal hydrothorax seems to have been justified, a larger multicenter study is needed to compare survival with and without pleuroamniotic shunting.

Blood pressure estimation in the human fetal descending aorta.

The objectives of this study were to estimate fetal blood pressure non‐invasively from two‐dimensional color Doppler‐derived aortic blood flow and diameter waveforms, and to compare the results with invasively derived human fetal blood pressures available from the literature.