The effect of epidural anaesthesia for caesarean section on maternal uterine and fetal umbilical artery blood flow velocity waveforms

The blood flow resistance in the maternal uteroplacental and fetal umbilical artery circulation was studied in eight otherwise normal patients undergoing elective lower segment caesarean section. The systolic/diastolic A/B ratio (the ratio of peak systolic to least diastolic flow velocity) for the uteroplacental and fetal umbilical circulation was determined from the artery blood flow velocity-time waveform and used as an index of blood flow resistance. Each patient received a 1 litre intravenous crystalloid infusion before an epidural bupivicaine injection. Both crystalloid infusion and epidural anaesthesia resulted in a significant decrease in the maternal uteroplacental systolic/diastolic (A/B) ratios, associated with a decrease in fetal umbilical artery A/B ratio. This study suggests a beneficial fetal effect from the improved maternal uterine perfusion after epidural anaesthesia.     

The effect of epidural anaesthesia for caesarean section on maternal uterine and fetal umbilical artery blood flow velocity waveforms

Summary. The blood flow resistance in the maternal uteroplacental and fetal umbilical artery circulation was studied in eight otherwise normal patients undergoing elective lower segment caesarean section. The systolic/diastolic A/B ratio (the ratio of peak systolic to least diastolic flow velocity) for the uteroplacental and fetal umbilical circulation was determined from the artery blood flow velocity-time waveform and used as an index of blood flow resistance. Each patient received a 1 litre intravenous crystalloid infusion before an epidural bupivicaine injection. Both crystalloid infusion and epidural anaesthesia resulted in a significant decrease in the maternal uteroplacental systolic/diastolic (A/B) ratios, associated with a decrease in fetal umbilical artery A/B ratio. This study suggests a beneficial fetal effect from the improved maternal uterine perfusion after epidural anaesthesia.     

The use of an indwelling Doppler probe to study acute changes in umbilical artery waveforms in the fetal sheep

A chronic sheep model for Doppler umbilical vascular analysis was developed, in which indwelling Doppler probes were used. These were designed with a fixed angle of insonation and implanted directly on the umbilical cord to register umbilical artery velocity waveforms. The fetuses in eight pregnant ewes underwent maternal aortic and umbilical cord constrictions producing serial blood flow reductions. Occlusion of the umbilical cord and maternal aorta caused distinctly different waveforms. Cord occlusion produced an immediate response with an elevated systolic/diastolic ratio and disappearance of diastolic velocity. Maternal aortic occlusion produced a delayed response with drops in both systolic and diastolic velocity; diastolic velocity never reached zero. Although systolic/diastolic ratios are believed to reflect placental resistance, the maintenance of the systolic/diastolic ratio with diminution of systolic velocity suggests declining fetal cardiac output as an additional factor. It is possible to differentiate uteroplacental from umbilicoplacental insufficiency by Doppler methods. With technologic improvements Doppler ultrasonography may allow better analysis of acute stressful conditions during human labor.     

Fetal and maternal hemodynamic responses to exercise in pregnancy assessed by Doppler ultrasonography

It is common for women to undertake vigorous exercise in the late phase of pregnancy. This may have detrimental effects on the blood flow to the uterus and placenta or from the fetus to the placenta. Fifteen pregnant women with no obstetric or medical complications were subjected to a 5-minute exercise period. The maternal heart rate and blood pressure were elevated after exercise. The uteroplacental and umbilical circulations were assessed with Doppler ultrasonography. The ratio of the systolic/diastolic velocity in the uterine artery was elevated, which suggests that uteroplacental vascular resistance increased. The fetal heart rate was elevated after exercise, whereas the systolic/diastolic velocity ratio in the umbilical artery was unaltered. We conclude that moderate maternal exercise causes increased resistance to blood flow in the uterine circulation, whereas the umbilical circulation remains unaltered.     

Umbilical artery and uteroplacental velocimetry in pregnancies complicated by idiopathic low birthweight centile.

Umbilical artery and uteroplacental Doppler flow velocity waveforms were studied in 35 pregnancies complicated by idiopathic low birthweight centile. Thirty fetuses (86%) were below the 5th centile birthweight for gestation. Fifteen (43%) had an abnormal umbilical artery systolic to diastolic ratio. Uteroplacental waveforms were recorded in 29 of the 35 pregnancies and five (17%) showed an abnormal systolic to diastolic ratio. Abnormal uteroplacental systolic to diastolic ratios were associated with a significantly earlier gestational age at delivery and significantly more cesarean sections for fetal distress compared with normal uteroplacental systolic to diastolic ratios (p less than or equal to 0.01). The absence of umbilical artery end-diastolic frequencies was associated with a significantly earlier gestational age at delivery compared with the presence of umbilical artery end-diastolic frequencies (p less than 0.005). No differences in pregnancy outcome were observed comparing normal with abnormal amniotic fluid volume assessment. These findings suggest that Doppler studies may be useful in estimating the risk of adverse perinatal outcome for small for gestational age fetuses with no identifiable cause.     

Doppler umbilical and uterine flow waveforms in severe pregnancy hypertension

Summary. Doppler studies of the umbilical and uteroplacental bed arterial flow velocity waveforms were performed in a series of women suffering from severe proteinuric pregnancy hypertension. Ninety-five women were studied and the mean interval between the last study and delivery was 1–4 days. An abnormally elevated umbilical artery systolic:diastolic (AB) ratio was present in 61 (64%) of the women. All 10 perinatal deaths were associated with pregnancies with an abnormal umbilical artery AB ratio. An elevated umbilical artery AB ratio was significantly associated with small-for-gestation and neonatal morbidity. Infants associated with extremely high umbilical artery AB ratios (≥ 99th centile) spent twice as long in the neonatal nursery as those with a lower value. There was no relation between the duration of hypertension and the umbilical study result. The uteroplacental bed artery flow velocity waveform did not correlate with fetal or neonatal mortality or morbidity. Patients with abnormal uteroplacental AB ratios also had abnormal umbilical artery AB ratios. We conclude that an abnormal fetal umbilical artery Doppler flow velocity waveform correlates with adverse fetal outcome in severe proteinuric pregnancy hypertension and suggest that the associated placental lesion may precede the maternal hypertension.     

Doppler umbilical and uterine flow waveforms in severe pregnancy hypertension

Doppler studies of the umbilical and uteroplacental bed arterial flow velocity waveforms were performed in a series of women suffering from severe proteinuric pregnancy hypertension. Ninety-five women were studied and the mean interval between the last study and delivery was 1.4 days. An abnormally elevated umbilical artery systolic:diastolic (AB) ratio was present in 61 (64%) of the women. All 10 perinatal deaths were associated with pregnancies with an abnormal umbilical artery AB ratio. An elevated umbilical artery AB ratio was significantly associated with small-for-gestation and neonatal morbidity. Infants associated with extremely high umbilical artery AB ratios (greater than or equal to 99th centile) spent twice as long in the neonatal nursery as those with a lower value. There was no relation between the duration of hypertension and the umbilical study result. The uteroplacental bed artery flow velocity waveform did not correlate with fetal or neonatal mortality or morbidity. Patients with abnormal uteroplacental AB ratios also had abnormal umbilical artery AB ratios. We conclude that an abnormal fetal umbilical artery Doppler flow velocity waveform correlates with adverse fetal outcome in severe proteinuric pregnancy hypertension and suggest that the associated placental lesion may precede the maternal hypertension.     

Qualitative assessment of maternal uterine and fetal umbilical artery blood flow and resistance in laboring patients by Doppler velocimetry

The purpose of this study is to evaluate the effect of uterine contractions during labor on both the uterine and the umbilical circulations. Twenty-seven patients in active labor were studied by continuous-wave Doppler velocimetry. Umbilical, left uterine, and right uterine arterial waveforms were obtained before, during, and after peak uterine contractions, and the ratio of maximum systolic and minimum diastolic velocities was calculated. Fifteen patients showed absent flow in end diastole on the uterine artery waveform and had significantly higher intra-amniotic pressures (64.5 +/- 3.5 mm Hg) during the peak amplitude of the uterine contraction compared with the 12 patients with maintained end diastolic flow (46.5 +/- 2.6 mm Hg; p less than 0.05). During the peak amplitude of the uterine contractions the 12 patients maintaining end-diastolic flow had significantly higher systolic/diastolic ratios in the uterine artery (6.5 +/- 1.5) compared with either before or after a contraction (2.1 +/- 0.15 and 2.0 +/- 0.2, respectively; p less than 0.05). Also, these 12 patients showed a linear relationship between the systolic/diastolic ratio and the intrauterine pressure. However, no differences were observed in the umbilical artery systolic/diastolic ratios before, during, or after a contraction in the intensity range studied. On the contrary, during contractions an increase in uterine artery resistance occurs with decreased or absent end-diastolic flow, which bears an inverse linear relationship to the intensity of the contraction. This suggests that during uterine contractions the human fetus continues to have uninterrupted fetoplacental blood flow, whereas the degree of interruption or reduction in uteroplacental blood flow is dependent on the intensity of uterine contraction.     

Umbilical artery flow velocity waveforms during spinal anesthesia

The umbilical artery Doppler flow velocity waveform was recorded during spinal anaesthesia prior to elective caesarean section in 15 uncomplicated pregnancies. Although spinal anaesthesia was associated with a significant fall in maternal systolic and diastolic blood pressure, there was no change in the umbilical artery Pulsatility Index either after preloading the maternal circulation with 750-1000 ml of Hartman's solution or for the first 15 min after subarachnoid injection of 0.5% bupivacaine. The fetal heart rate fell after preloading the maternal circulation, but was unchanged by the administration of bupivacaine. There was a weak negative correlation between fetal heart and the umbilical artery Pulsatility Index. These observations suggest that in normal pregnancy, spinal anaesthesia has no detrimental effect on the umbilical artery Pulsatility Index.     

The utility of umbilical artery Doppler investigation in women with the HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome

OBJECTIVE: Our aim was to study the utility of umbilical artery Doppler velocimetry in the management of women with the HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome. STUDY DESIGN: Fetuses of women with the HELLP syndrome underwent ultrasonographic evaluation at initial presentation. An abnormal umbilical artery Doppler study was defined as a systolic/diastolic ratio >5.0. The systolic/diastolic ratios were correlated with outcome variables including laboratory findings, latency, mode of delivery, and birth weight. RESULTS: Fifty women were enrolled into the study. Eighteen of the fetuses (36%) had abnormal waveforms, with 8 fetuses demonstrating either absent or reversed end-diastolic umbilical artery blood flow. The mean umbilical artery systolic/diastolic ratio was significantly higher for fetuses with intrauterine growth restriction or who were small for gestational age than for those without these diagnoses (P =.001, for each). No correlation was observed between the systolic/diastolic ratio and the laboratory findings at admission, the degree of hypertension at admission, or the latency to delivery (all, P >.05). No woman with a fetus at a viable gestational age having abnormal Doppler waveforms had a successful vaginal delivery. CONCLUSION: Abnormal umbilical artery Doppler velocimetry is associated with a higher risk of fetal growth restriction and a high likelihood of cesarean delivery. These values were not correlated with the severity of maternal disease.     

Flow velocity waveforms in uterine and umbilical arteries during the angiotensin II sensitivity test

The angiotensin II sensitivity test has been used to predict the development of hypertension during pregnancy. We investigated the systolic/diastolic ratios of flow velocity waveforms in the uterine and umbilical arteries by means of a color Doppler system in 15 healthy women at 24 to 26 weeks' gestation. A significant increase (p less than 0.001) was observed in the systolic/diastolic ratio in the uterine artery, which was unaffected by the location of the placenta. In five women a differential effect of angiotensin II on the systemic diastolic blood pressure and on the systolic/diastolic was observed: the uterine circulation appeared to have a slower response and a faster recovery than the diastolic blood pressure. No changes in the systolic/diastolic ratio in the umbilical artery were observed.     

The application of uterine and umbilical artery velocimetry to the antenatal supervision of pregnancies complicated by maternal sickle hemoglobinopathies

To assess the efficacy of Doppler flow velocimetry in predicting fetal compromise and neonatal outcome in pregnant women with sickle cell hemoglobinopathies, a prospective study was conducted of 96 patients, 48 with sickle cell hemoglobinopathy (8 with SS and 40 with AS hemoglobin) and 48 low-risk AA hemoglobin controls. All subjects were followed biweekly from the third trimester of pregnancy through delivery with uterine and umbilical artery velocimetry, nonstress, tests, and hematocrit and blood pressure measurements. An abnormal systolic/diastolic ratio was defined as a value greater than or equal to 3. The incidence of abnormal systolic/diastolic ratios for uterine or umbilical arteries was significantly higher in pregnant women with SS hemoglobin (88%) when compared with patients with AS (7%) and AA (4%) hemoglobin. In addition, the abnormal systolic/diastolic ratios for both umbilical and uterine arteries are correlated with abnormal nonstress test results. The nonstress test results became abnormal on average 3 weeks after the systolic/diastolic ratios did. The presence of abnormal systolic/diastolic ratios for umbilical and uterine arteries is predictive of fetal distress and infants small for gestational age. The high incidence of concordant uterine and umbilical artery abnormal systolic/diastolic ratios in pregnant women with SS hemoglobinopathy, which were identified earlier than were abnormal nonstress results, suggests an important parameter in the monitoring of these high-risk pregnancies.     

Effect of orthostatic stress on umbilical Doppler waveforms in normal and hypertensive pregnancies.

OBJECTIVE: Our study examined the effects of orthostatic stress and maternal hemodynamics on umbilical systolic/diastolic ratios in normal and hypertensive pregnancies. STUDY DESIGN: Eighteen normal and 20 hypertensive third-trimester pregnancies were examined in the left lateral recumbent, sitting, and standing positions. Measurements included umbilical systolic/diastolic ratio, maternal blood pressure, maternal cardiac output, and maternal total peripheral resistance. RESULTS: All patients demonstrated a fall in cardiac output and a rise in total peripheral resistance with standing. No change in systolic/diastolic ratio occurred with change to the upright position in patients with normotension. Patients with hypertension exhibited a significant increase in umbilical systolic/diastolic ratio with postural change. The increase was more marked in women who had hypertension with elevated peripheral resistance. CONCLUSION: Patients with hypertension are at increased risk of elevation of systolic/diastolic ratio with postural change; women with high-resistance hypertension may be at highest risk.     

Diurnal blood pressure variation in the evaluation of early onset severe pre-eclampsia

OBJECTIVE: To study the association between diurnal variation in blood pressure, the mean daily blood pressure and various complications of pregnancy in patients presenting with severe pre-eclampsia before 34 weeks' gestation. STUDY DESIGN: Forty-four women presenting to a tertiary hospital in South Africa with severe pre-eclampsia between 28 and 34 weeks' gestation were managed expectantly for at least 8 days. We measured maternal blood pressure every 30 min with the pregnancy validated Spacelabs 90209 automated blood pressure monitor for 24h periods on alternative days. The mean 24-h diastolic blood pressure measurement, the mean diastolic blood pressure for daytime and nighttime, the day-night blood pressure difference and the night-day ratio were compared with the occurrence of abruptio placentae, gestational age at delivery, neonatal intensive care unit admission, birth weight, abnormal umbilical artery Doppler FVW and reason for delivery. RESULTS: One hundred and seventy-six 24-h studies were analyzed. The day-night blood pressure difference decreased with increasing mean diastolic blood pressure (r=-0.323, p<0.0001). A combination of normal mean diastolic blood pressure and normal day-night blood pressure difference was associated with increased gestational age and lower caesarean section rates. CONCLUSION: The combination of mean diastolic blood pressure and day-night blood pressure difference may be a supplementary measurement of disease severity in early onset severe pre-eclampsia and seems to be of prognostic value.     

Thromboxane synthetase inhibition produces maternal and fetal vasodilation during ovine pregnancy-induced hypertension: a Doppler flow velocimetric study.

Changes in maternal and fetal umbilical arterial vasoreactivity during ovine pregnancy-induced hypertension and following intravenous administration of CGS 12970 [3-methyl-2-(3-pyridyl)-1-indoleoctanoic acid] were assessed. Continuous wave Doppler flow velocimetry was used to assess vascular reactivity during normotensive baseline, during ovine pregnancy-induced hypertension triggered by a 72-hour fast, and following thromboxane synthetase inhibition with CGS 12970. Uterine and umbilical arterial systolic/diastolic flow ratios increased significantly with the onset of sustained hypertension. After thromboxane synthetase inhibition, uterine and umbilical artery systolic/diastolic flow ratios were not different from baseline, and maternal blood pressure had returned to baseline values. These data indicate that thromboxane produces maternal and fetal vasoconstriction during ovine pregnancy-induced hypertension. Furthermore, these data provide strong evidence that thromboxane synthetase inhibition allows vasodilation, resulting in improved maternal and fetal condition.     

Misoprostol and dinoprostone therapy for labor induction: a Doppler comparison of uterine and fetal hemodynamic effects

OBJECTIVE: To compare the effect of misoprostol (PGE(1)) versus dinoprostone (PGE(2)) on blood flow in uteroplacental circulation during labor induction. STUDY DESIGN: Eighty-four women with indications for induction of labor were assigned to receive either misoprostol 50 microg per vagina every 4 h as needed or 0.5 mg doses of dinoprostone given intra-cervically every 6 h by means of a randomization table generated by computer. Doppler velocimetry of umbilical, uterine and arcuate arteries was performed immediately before and 2-3 h after the administration of misoprostol or dinoprostone. The SAS system was used to perform statistical analysis. RESULTS: There were no significant changes of pulsatility index (PI), resistance index (RI) and systolic/diastolic (S/D) ratio in umbilical arteries after both prostaglandin compounds. Vaginal application of misoprostol significantly increased all ratios in arcuate artery and S/D ratio in uterine artery. Intra-cervically dinoprostone significantly increased PI, RI and S/D ratio in arcuate and uterine arteries. CONCLUSIONS: Our results indicate that vaginal misoprostol and cervical dinoprostone administration increases uteroplacental resistance but does not affect umbilical blood flow. Misoprostol would be as safe and effective agent as dinoprostone for cervical ripening and labor induction.     

Comparison of low- and high-altitude Doppler velocimetry in the peripheral and central circulations of normal fetuses

OBJECTIVE: Our aim was to test the hypothesis that Doppler velocimetry of the peripheral and central circulations in normal fetuses is not affected by moderately high altitude (Denver, Colo-1609 m) compared with sea level (Milan, Italy-40 m). STUDY DESIGN: One hundred nineteen patients with singleton pregnancies underwent Doppler waveform analysis of the following: umbilical artery, uterine artery, middle cerebral artery, ductus venosus, and the tricuspid and mitral valves. RESULTS: Birth weights were reduced at Denver's altitude (P<.001). The early/late diastolic inflow ratios of the atrioventricular valves increased with gestational age (P<.01), whereas systolic/diastolic ratios of the uterine and umbilical arteries decreased with gestational age (P<.01). There were no Doppler velocimetry differences in any vessel between Denver's and Milan's altitudes. CONCLUSIONS: Gestational age has the same effect on Doppler index at both high and low altitudes. Moderately high altitude does not affect uteroplacental or fetal vascular Doppler index and may reflect normal acclimatization in the smaller Denver fetuses.     

The effects of epidural anesthesia on the Doppler velocimetry of umbilical and uterine arteries in normal term labor

To study the possible effects of epidural anesthesia on the Doppler velocimetry of the fetal umbilical and maternal uterine arteries, 15 normal term parturients were examined during active labor. Each Doppler study, conducted over 90 minutes after a 500-mL intravenous volume pre-load, was divided into three phases: 30 minutes of pre-anesthetic control, 30 minutes during epidural catheter placement and dosing, and 30 minutes after establishing effective regional blockade. During each phase, maternal blood pressure and pulse were monitored every 5 minutes, and continuous-wave Doppler recordings of the umbilical and uterine arteries were made at three separate intervals. Epidural placement and dosage techniques were similar for all patients; 0.25% bupivacaine solution was used and sensory levels of T6 obtained. The mean maternal systolic and diastolic blood pressures and pulse rate declined significantly, but no woman experienced hypotension. Mean systolic/diastolic ratios and pulsatility indices of the umbilical and uterine arteries did not change significantly during the study. We conclude that effective epidural anesthesia does not have a significant impact on Doppler flow characteristics of either the maternal or fetal umbilical vasculature, despite lowered maternal blood pressure and pulse rate.     

The relationship between the umbilical artery systolic/diastolic ratio and umbilical blood gas measurements in specimens obtained by cordocentesis

The purpose of this investigation was to prospectively determine the relationship between the umbilical artery systolic/diastolic ratio and the umbilical blood gases in samples obtained from 165 fetuses during diagnostic cordocenteses. In each instance the sample was the umbilical vein. The systolic/diastolic ratio was measured in a midsection of the umbilical cord. Analyses used stepwise, multiple linear regression. The mean +/- SEM gestation was 29 +/- 0.4 weeks; 72% of fetuses were greater than or equal to 25 weeks and were considered potentially viable. There was no relationship between the umbilical artery systolic/diastolic ratio and pH, PCO2, or PO2 in fetuses either less than 25 weeks' gestation or greater than or equal to 25 weeks' gestation but with systolic/diastolic ratios greater than or equal to the 95th percentile for control fetuses at 25 weeks' gestation with normal blood gas values (3.5). In fetuses greater than or equal to 25 weeks' gestation with systolic/diastolic ratios that exceeded 3.5 (n = 37), there was a strong relationship between the systolic/diastolic ratio and the umbilical venous PO2 (r = -0.68, p less than 0.0001), which was independent of gestational age. Each fetus with repetitively absent-reversed umbilical artery diastolic blood flow and a heart rate greater than 90 beats/min (n = 6) had blood gas measurements consistent with hypoxia and acidosis. This investigation suggests that factors that lead to an increase in the umbilical artery systolic/diastolic ratio are associated with a progressive impairment of placental gas exchange and that by the time diastolic flow is lost, hypoxemia is present.     

Effect of amniotomy on uteroplacental and fetoplacental flow velocity waveforms

Artificial rupture of fetal amnionic membranes is frequently performed in normally progressing spontaneous labor, although the maternal and fetal effects of the procedure have not been clearly defined. The effect of elective amniotomy on placental impedance to blood flow in the umbilical artery and arcuate branches of the uterine artery was determined by analysis of blood flow velocity waveforms (FVWs) recorded with continuous wave Doppler ultrasound in 15 pregnant women at term. All patients were in spontaneous, normally progressing labor after an uneventful pregnancy. Electronic fetal heart rate monitoring and real-time ultrasound examination of the fetuses were unremarkable. FVWs were obtained immediately before and after amniotomy. Fourteen patients progressed to spontaneous vaginal delivery, and one patient underwent repeat cesarean section for arrest of dilation in the active phase of labor. No maternal, fetal, or neonatal complications were recorded. Calculated mean systolic/diastolic ratios of FVWs obtained before and after amniotomy were compared by means of Wilcoxon's signed rank test, and no significant differences were found. We conclude that early elective amniotomy exerts no demonstrable deleterious effect on impedance to uteroplacental or fetoplacental blood flow in healthy women at term.