Harbinder S. Brar

Reverse end-diastolic flow velocity on umbilical artery velocimetry in high-risk pregnancies: An ominous finding with adverse pregnancy outcome

Systolic/diastolic ratios of umbilical velocimetry have been used to assess downstream placental vascular resistance. Reverse end-diastolic flow velocity during end diastole suggests extreme abnormality in waveform and resistance. We reviewed our experience of patients showing reverse end-diastolic flow velocity over a 2 1/2-year period. Out of 550 high-risk patients studied with umbilical velocimetry over this period, 12 patients showed the finding. All patients were delivered of small for gestational age fetuses and the perinatal mortality in this group was 50%. There was also significant perinatal morbidity as judged by cesarean section performed because of fetal distress, low Apgar scores, days in neonatal intensive care, prematurity, placental infarcts, and lethal anomalies. These findings suggest that reverse end-diastolic velocity on umbilical velocimetry is associated with catastrophic perinatal outcome, and aggressive perinatal management may be advised in this group of patients.

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.

Intrapartum Doppler velocimetry, amniotic fluid volume, and fetal heart rate as predictors of subsequent fetal distress. I. An initial report.

This study examines the usefulness of umbilical artery Doppler velocimetry, amniotic fluid volume assessment, and fetal heart rate data in the early intrapartum period as predictors of subsequent fetal distress. A total of 109 patients seen in the latent phase of labor in the labor and delivery area were studied. Both an abnormal initial fetal heart rate and an amniotic fluid index less than or equal to 5.0 cm were associated with a significant increase in the incidence of intrapartum fetal distress. Conversely, a systolic/diastolic ratio greater than 3.0 by Doppler ultrasonography was not associated with increased fetal morbidity. Overall, the sensitivities, specificities, and positive predictive values of the fetal heart rate tracing and the amniotic fluid volume assessment were comparable. Doppler systolic/diastolic ratios showed very poor sensitivity and positive predictive value. We conclude that the fetal heart rate tracing or the assessment of amniotic fluid volume in the early intrapartum period are reasonable predictors of subsequent fetal condition. The lack of patients with the absence of or reverse umbilical velocity preclude conclusions with regard to Doppler systolic/diastolic ratios for this purpose.

Increased fetoplacental active renin production in pregnancy-induced hypertension

Since pregnancy-induced hypertension is associated with impaired uteroplacental blood flow, we studied fetoplacental and maternal renin production in controls and subjects with pregnancy-induced hypertension. We measured total, active, and inactive (pro-) renin in maternal serum, fetal arterial and venous blood, and chorion homogenate in eight normotensive term patients and 18 patients with pregnancy-induced hypertension. No differences in active or prorenin were found in maternal blood from normal women or patients with pregnancy-induced hypertension. In contrast, fetal artery and vein, as well as chorionic tissue, contained significantly higher active renin in pregnancy-induced hypertension compared with normal subjects. No difference in fetal or chorionic prorenin was seen in the two groups. Thus active to total renin ratio was higher in the fetus and chorion of subjects with pregnancy-induced hypertension, which suggests enhanced active renin production. These results suggest that pregnancy-induced hypertension is associated with increased activity of the renin-angiotensin system in the fetoplacental unit, which is not reflected in the maternal circulation. This may be an attempt by the fetus and chorionic membranes to maintain vascular homeostasis in the face of altered uteroplacental blood flow.

Uteroplacental unit as a source of elevated circulating prorenin levels in normal pregnancy

Circulating levels of inactive renin, that is, prorenin, are increased in normal pregnant women. To determine whether the uteroplacental unit secretes prorenin into the maternal circulation, we measured enzymatically active and inactive renin in plasma simultaneously obtained from the radial artery and uterine vein of 12 normotensive, nonlaboring patients undergoing elective cesarean section at term. We also measured these forms of renin in the umbilical arterial and venous blood of these patients. Our data reveal that the levels of inactive renin in both arterial and uterine venous blood of normal pregnant women are significantly higher than in peripheral venous blood of nonpregnant, normotensive control subjects; normotensive term patients have a ratio of plasma inactive to active renin of 9:1 in contrast to the 1:1 ratio in normotensive nonpregnant subjects; there is a significant uterine arteriovenous difference of prorenin (66.2 +/- 24.4 ng/ml/hr, p less than 0.05) but not of active renin (1.8 +/- 1.5 ng/ml/hr, not significant). These results suggest that the uteroplacental unit contributes to the elevated prorenin levels at term pregnancy.

Maternal and fetal blood flow velocity waveforms in patients with preterm labor prediction of successful tocolysis

Umbilical and uterine artery velocimetry was performed using continuous-wave Doppler ultrasound (Angioscan III) in 60 patients in preterm labor. Peak-systolic/end-diastolic ratios were calculated according to previously described techniques. All measurements were made before tocolytic therapy was begun: magnesium sulfate (n = 40) or ritodrine (n = 20). The mean gestational age was 33.1 +/- 1.5 weeks (range 29 to 36 weeks). Twelve (20%) patients had elevated (greater than 2.6) pretherapy uterine peak-systolic/end-diastolic ratios, 10 (16.7%) patients had elevated (greater than 3.5) pretherapy umbilical peak-systolic/end-diastolic ratios, and in eight (13.3%) patients both ratios were elevated. In seven (58.4%) of the 12 patients with elevated uterine peak-systolic/end-diastolic ratios, six (60%) of the 10 patients with elevated umbilical peak-systolic/end-diastolic ratios, and five (62.5%) of the eight patients with both ratios elevated tocolytics failed and the women were delivered within 48 hours, compared with seven (14.6%) of 48, eight (16%) of 50, and six (13.0%) of 46 with normal ratios, respectively (p less than 0.05). We conclude that patients in preterm labor with elevated pretherapy uterine and/or umbilical peak-systolic/end-diastolic ratios are more likely to fail tocolysis therapy and be delivered preterm than those with normal ratios. It may therefore be useful to include umbilical and uterine velocimetry in the initial evaluation of preterm labor.

Maternal and fetal blood flow velocity waveforms in patients with preterm labor: Relationship to outcome

Elevated systolic/diastolic ratios obtained by umbilical and uterine velocimetry have been used to predict adverse pregnancy outcome. We performed pretherapy umbilical and uterine velocimetry by means of continuous-wave Doppler ultrasonography on 92 patients who came for treatment in preterm labor. Fourteen (15.2%) and 12 (13%) patients had elevated uterine (greater than 2.6) and umbilical (greater than 3.5) systolic/diastolic ratios, respectively, and 9 (9.8%) patients had both ratios elevated. Overall 17 (18.5%) patients had at least one abnormal systolic/diastolic ratio. Patients with abnormal Doppler waveforms had a significantly shorter gestation, infants with lower birth weights, and a higher incidence of adverse pregnancy outcome as determined by meconium, cesarean section for fetal distress, low 1- and 5-minute Apgar scores, and days in the neonatal intensive care unit, compared with patients with normal systolic/diastolic ratios. There was no significant difference in the ability of uterine, umbilical, or combined velocimetry to predict preterm birth or adverse pregnancy outcome. Doppler studies in preterm labor patients may help to identify patients at increased risk for preterm birth and poor pregnancy outcome. Further studies are warranted to assess its usefulness in the evaluation of these patients.

Antepartum improvement of abnormal umbilical artery velocimetry: Does it occur?

Absence of end-diastolic velocity on umbilical artery velocimetry suggests extreme elevation of placental vascular resistance and is associated with adverse pregnancy outcome. This study was undertaken to assess whether antepartum improvement of abnormal umbilical artery waveforms occurs. Thirty-one fetuses identified with absence of end-diastolic velocity between July 1985 and December 1987 at Womens Hospital underwent sequential umbilical artery velocimetry at 1- to 3-day intervals. The presence of end-diastolic velocity on subsequent scans was considered an improvement in waveforms. The mean diagnosis-to-delivery interval (20.5 +/- 4 days), gestational age at delivery (32.5 +/- 1.2 weeks), and birth weight (1440 +/- 210 gm) were significantly higher in five fetuses that showed improvement in waveforms, compared with the 26 fetuses that did not show improvement in waveforms (9.5 +/- 3.5 days, 29.5 +/- 0.9 weeks, and 940 +/- 70 gm, respectively). Ten perinatal deaths occurred, for a perinatal mortality rate of 32.3%. There was significant perinatal morbidity in the overall group as judged by intrauterine growth retardation, meconium, 5-minute Apgar scores less than 7, and cesarean section for fetal distress. We conclude that although absence of end-diastolic velocity is associated with adverse pregnancy outcome, antepartum improvement in umbilical artery waveforms occurred in 15% of the fetuses studied and was associated with an improvement in perinatal outcome. Factors that influenced this improvement, though unclear, might be related to maternal bed rest or medication and require further investigation.

Antepartum fetal surveillance: the biophysical profile.

In summary, it appears, based on a cumulative experience of more than 15,000 patients from several centers, that fetal biophysical profile scoring holds promise as an improved method of fetal risk detection. Antepartum detection, classification, determination of severity, and ultimately, treatment of the fetus at risk for death and damage in utero form the basis of modern perinatal medicine. It remains to be determined whether addition of further variables or refinement of existing variables will improve accuracy still further. The assessment of multiple biophysical variables and responses to intrinsic and extrinsic stimuli is helpful in differentiating a normal sleeping fetus from an asphyxiated one.

Relationship of systolic/diastolic ratios from umbilical velocimetry to fetal heart rate.

We assessed the relationship between systolic/diastolic ratios as determined by umbilical velocimetry to fetal heart rate. Umbilical velocimetry was performed with continuous-wave Doppler ultrasound and systolic/diastolic ratios and fetal heart rate for the corresponding cardiac cycles were calculated in four groups of patients. Group 1 consisted of 30 patients undergoing antepartum fetal testing; systolic/diastolic ratios were found to be significantly lower (mean +/- SD, 2.0 +/- 0.15) during an evoked fetal heart rate acceleration with an artificial larynx than either before (2.4 +/- 0.14) or after the acceleration (2.35 +/- 0.10, p less than 0.01). In 20 patients with pyelonephritis (group 2), systolic/diastolic ratios were significantly lower during initial fetal tachycardia (1.6 +/- 0.21) as compared with those obtained after its resolution (2.1 +/- 0.12, p less than 0.08). In the 25 patients with chorioamnionitis in group 3, systolic/diastolic ratios were significantly higher during initial fetal tachycardia (1.4 +/- 0.21) than after its resolution (1.9 +/- 0.15, p less than 0.05). Twenty patients in labor (group 4) had 10 serial measurements at 1 to 2-hour intervals of systolic/diastolic ratio and FHR. Least-squares regression of each patient showed a negative slope that differed statistically from zero (p less than 0.05). There were no patients with elevated systolic/diastolic ratios greater than 3.0 in any group and all patients delivered fetuses appropriate for gestational age. These findings suggest an inverse relationship between systolic/diastolic ratio and fetal heart rate. Additionally, an alteration in fetal heart rate within the range studied does not itself produce abnormal ratios. Therefore normalization of the systolic/diastolic ratio for heart rate may be considered in clinical studies for statistical analysis and comparison but may have little practical or clinical relevance when the ratios are abnormal.