Venous pulsation in the fetal left portal branch: the effect of pulse and flow direction.

OBJECTIVE: To determine whether the waveform in the left portal branch is reciprocal to the waveform found in the ductus venosus and umbilical vein due to difference in pulse direction compared to flow. METHODS: Ten fetuses (gestational age, 18-33 weeks), six with intrauterine growth restriction, three with non-immune hydrops and one with sacrococcygeal teratoma, were examined using ultrasound imaging and pulsed Doppler. Techniques were adjusted to record simultaneously the waveform from neighboring sections of the veins, relate wave components to each other and determine degree of pulsatility. The corresponding vessel diameters were determined. ANOVA with t-test or Wilcoxon signed rank test was used to compare paired measurements. RESULTS: Pulsation in the left portal branch was noted in all fetuses. The pulsatility index was higher than in the umbilical vein (P = 0.005) and the diameter smaller (P = 0.001). In the left portal branch the atrial contraction wave appeared as a velocity peak while there was a nadir during ventricular systole. Simultaneous recordings showed that the waveform was reciprocal to that found in the ductus venosus and umbilical vein. In three cases an augmented pulsatility represented a pendulation of blood in the left portal branch with time-averaged velocity near zero. CONCLUSIONS: The velocity waveform recorded in the left portal vein is an inverse image of that in the ductus venosus, proving that pulse wave and blood flow run in the same direction in the left portal vein. Low compliance (i.e. small diameter) is probably a main reason for the high incidence of pulsation in this vein. Time-averaged velocity near zero recorded in three fetuses indicates that this area acts also as a watershed.

Is the liver of the fetus the 4th preferential organ for arterial blood supply besides brain, heart, and adrenal glands?

In this study we compared the distribution of blood flow to the liver in growth-retarded fetuses whose estimated weight was < 5th centile with normal-weight fetuses. As expected, the relative venous blood flow to the liver was reduced, with blood flowing preferentially through the ductus venosus. However, the total blood supply seemed to be maintained by a concomitant, significant increase in arterial blood flow through the hepatic artery. Absolute flow velocities such as the peak, minimum diastolic and temporal average velocities were changed, as was the flow waveform. Effectively, the deficiency in venous supply was made up for by an increase in arterial blood flow. This compensatory effect may be crucial for maintaining liver function in times of low portal venous blood supply. It thus makes sense to regard the liver as the fourth preferential organ for arterial blood supply in the compromised fetus, besides heart, brain, and adrenals.

The umbilical ring--the first rapid in the fetoplacental venous system.

In this study, the effect of the umbilical ring on blood flow velocities in the umbilical vein was examined using Doppler sonography. The maximum blood flow velocity in the umbilical vein was measured just before and behind the umbilical ring in eleven normal singleton pregnancies at 24-34 gestational weeks. The maximum velocity increased in each single case (p < 0.0001), the mean increase was from 16 cm/sec to 31 cm/sec. Thus, the narrowing of the umbilical ring serves as the first rapid in venous fetoplacental circulation. The physiological role of the acceleration of venous blood flow remains to be elucidated. Possible functions include stabilizing venous blood flow or preferential streaming.

The predictive value of fetal heart rate monitoring: a retrospective analysis of 2165 high-risk pregnancies.

The predictive value of fetal heart-rate monitoring on fetal well-being was studied in 2165 high-risk pregnancies. 1883 reactive nonstress test (NST) patterns and 278 nonreactive NST patterns and 4 cases of sinusoidal pattern were obtained. Oxytocin challenge test (OCT) was applied to 263 nonreactive cases. OCT was not applied to 15 cases out of 278 nonreactive NST cases, because of placenta previa, abruptio placenta and previous cesarean section. There were 155 cases with negative OCT, 84 cases with positive OCT and 24 cases with equivocal, prolonged or severe variable decelerations. Sensitivity and specificity were for NST 50 and 88% and for OCT 60 and 67%. The positive and negative predictive values were 11 and 98% for NST and 18 and 93% for OCT. It is concluded that the reactive nonstress test is a reliable test for good outcome but a positive oxytocin challenge test is not a reliable test for poor outcome. Additional procedures are necessary such as assessment of fetal growth, doppler velocity waveforms and fetal biophysical profile to avoid unnecessary obstetric interventions and to reach good fetal outcome.

FHR monitoring and perinatal mortality in high-risk pregnancies.

The aim of the study was to evaluate the effect of the introduction of fetal heart rate monitoring on perinatal mortality rates in high-risk pregnancies. Results were compared with the perinatal mortality rates published previously from our clinics. The study group consisted of 2165 high-risk pregnant patients. The perinatal mortality rate in the study group was 28.6%, and the corrected rate 15.9%. The rates were significantly lower in comparison with the total perinatal mortality rates in former years. We are convinced that fetal heart-rate monitoring resulted in a significant decrease in the perinatal mortality rate. Although the increased use of fetal monitoring cannot reduce perinatal mortality resulting from problems such as genetic disorders, this study shows improved outcomes for many high-risk conditions, in particular postmature pregnancies.