J. W. Wladimiroff

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.

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.

Prenatal diagnosis of fetal abdominal wall defects: a retrospective analysis of 44 cases.

Forty‐four fetal abdominal wall defects, consisting of 31 omphalocoeles, 11 cases of gastroschisis, and two body stalk anomalies (which are excluded from further analysis), were diagnosed at 12–39 weeks (median 26 weeks) of gestation. In 10/31 (32 per cent) cases of omphalocoele and in 4/11 (36 per cent) cases of gastroschisis, multiple congenital anomalies were diagnosed. A normal amount of amniotic fluid was present in 39 cases; in three cases of omphalocoele an abnormal amount of amniotic fluid (polyhydramnios, n=2; oligohydramnios, n=1) was seen. Prenatally, intrauterine growth retardation (IUGR) was diagnosed in each type of anomaly only once, although the birth weight was below the tenth centile in 23 per cent of omphalocoeles and in 36 per cent of cases of gastroschisis. An abnormal prenatal karyotpye was established in 5/25 (20 per cent) cases of omphalocoele versus none in the gastroschisis group. In 36 cases an expectant obstetric management was followed, and in six cases of omphalocoele the pregnancies were terminated because of severe multiple anomalies (n=3) or an abnormal prenatal karyotype (n=3). The preterm delivery rate (excluding terminations) was 12/25 (48 per cent) in the omphalocoele subgroup versus 8/11 (73 per cent) in the gastroschisis subgroup. The Caesarean section rate was almost identical (19 versus 18 per cent) in both subgroups; the majority (n=5) were performed to protect the abdominal wall defect. The overall survival rate was 39 per cent in the omphalocoele group; in all surviving infants this was the sole congenital anomaly and in each instance there was a normal karyotype. In the gastroschisis group, 8/11 (72 per cent) infants survived, of which two children also displayed unilateral hydronephrosis.

Fetal brain/liver volume ratio and umbilical volume flow parameters relative to normal and abnormal human development

To estimate fetal brain volume from head circumference and published postmortem data; to determine normal values for the fetal brain/liver volume ratio relative to gestational age; to establish the relationship between the brain/liver volume ratio and fetal circulatory parameters during normal and restricted (SGA) fetal growth.

The role of three‐dimensional ultrasound in visualizing the fetal cranial sutures and fontanels during the second half of pregnancy

The aim of this study was to evaluate the significance of three‐dimensional (3D) ultrasound in visualizing fetal cranial sutures and fontanels and to determine factors that could influence visualization and image quality.

Assessment of fetal left cardiac isovolumic relaxation time in appropriate and small-for-gestational-age fetuses

Left ventricular isovolumic relaxation time was studied in 22 appropriate-for-gestational-age fetuses (AGA, 26-40 wk) and 12 small-for-gestational-age fetuses (SGA, 29-37 wk). Left ventricular isovolumic relaxation time was determined from the interval between aortic valve closure and maximal left atrial dimension by M-mode, and from the interval between aortic valve closure artefact and onset of transmitral flow by pulsed Doppler. Mean left ventricular isovolumic relaxation time by M-mode (36 +/- 6 ms) and by pulsed Doppler (49 +/- 10 ms) were significantly different (p < 0.05) in AGA while this was not so in SGA (56 +/- 10 ms vs. 60 +/- 8 ms). A significant difference (p < 0.05) in mean left ventricular isovolumic relaxation time by M-mode existed between AGA (36 +/- 6 ms) and SGA (56 +/- 10 ms), whereas this was not so for pulsed Doppler (48 +/- 10 ms vs. 60 +/- 8 ms). Mean left ventricular isovolumic relaxation time by Doppler was significantly larger (mean difference 14 +/- 8 ms; p < 0.05) than by M-mode in AGA. However, there was no difference in mean left ventricular isovolumic relaxation time between the two ultrasound modalities in SGA. These data suggest synchronization of mitral cusp separation and transmitral blood flow in the SGA fetus. We speculate that, in the SGA fetus, delayed left ventricular isovolumic relaxation time may reflect cardiac diastolic dysfunction.

Three-dimensional sonographic determination of normal fetal mandibular and maxillary size during the second half of pregnancy

To explore the various ways of obtaining fetal maxillary and mandibular size with three‐dimensional (3D) ultrasound, with a view to developing a tool for identifying minor anomalies in the lower facial region.

Pulse pressure assessment in the human fetal descending aorta

Pulsatile vessel diameter recordings were obtained at two different levels of the fetal descending aorta in ten third-trimester human fetuses using an echo-tracking system. A derivation of the Moens-Korteweg equation was used to estimate the pulse pressure amplitude in this vessel. The positive phase of the first derivative of the diameter curves was cross correlated to assess the propagation time of the pulse wave. It is postulated that this method minimises the measuring errors resulting from diameter pulse wave changes during propagation along the longitudinal axis of the descending aorta. It was estimated from repeated measurements that approximately 13 recordings of 5.2 s each are required to assess the mean pulse pressure amplitude for an individual fetus with an estimated random error of 10%.

EFFECT OF MATERNAL POSTURE ON THE UMBILICAL ARTERY FLOW VELOCITY WAVEFORM

The effect of maternal postural changes on the umbilical artery flow velocity waveform, fetal heart rate and maternal blood pressure was studied in 27 normal singleton pregnancies between 23 and 36 weeks of gestation. A statistically significant change in umbilical artery Pulsatility Index (PI) was established for both maternal standing to supine position (rise) and supine to standing position (drop). These PI changes were not related to gestational age. A statistically significant drop in maternal systolic blood pressure was observed from standing to supine position. The rise in umbilical PI resistance when changing from standing to supine position may be caused by the sluice flow mechanism.