The correlation of biochemical monitoring versus umbilical flow velocity measurements of the human fetus

Fetal growth restriction: current knowledge

BACKGROUND

Fetal growth restriction (FGR) is a condition that affects 5-10% of pregnancies and is the second most common cause of perinatal mortality. This review presents the most recent knowledge on FGR and focuses on the etiology, classification, prediction, diagnosis, and management of the condition, as well as on its neurological complications.

METHODS

The Pubmed, SCOPUS, and Embase databases were searched using the term "fetal growth restriction".

RESULTS

Fetal growth restriction (FGR) may be classified as early or late depending on the time of diagnosis. Early FGR (<32 weeks) is associated with substantial alterations in placental implantation with elevated hypoxia, which requires cardiovascular adaptation. Perinatal morbidity and mortality rates are high. Late FGR (≥32 weeks) presents with slight deficiencies in placentation, which leads to mild hypoxia and requires little cardiovascular adaptation. Perinatal morbidity and mortality rates are lower. The diagnosis of FGR may be clinical; however, an arterial and venous Doppler ultrasound examination is essential for diagnosis and follow-up. There are currently no treatments to control FGR; the time at which pregnancy is interrupted is of vital importance for protecting both the mother and fetus.

CONCLUSION

Early diagnosis of FGR is very important, because it enables the identification of the etiology of the condition and adequate monitoring of the fetal status, thereby minimizing risks of premature birth and intrauterine hypoxia.

Prediction of intrapartum fetal compromise using the cerebroumbilical ratio: a prospective observational study

OBJECTIVE

To investigate the use of the fetal cerebroumbilical ratio to predict intrapartum compromise in appropriately grown fetuses.

STUDY DESIGN

A prospective observational study set at Queen Charlotte's and Chelsea hospital, London, UK. Fetal biometry and Doppler resistance indices were measured in 400 women immediately before established labor. Labor was then managed according to local protocols and guidelines, and intrapartum and neonatal outcome details recorded.

RESULTS

Infants delivered by cesarean section for fetal compromise had significantly lower cerebroumbilical ratios than those born by spontaneous vaginal delivery (1.52 vs 1.82, P ≤ .001). Infants with a cerebroumbilical ratio <10th percentile were 6 times more likely to be delivered by cesarean section for fetal compromise than those with a cerebroumbilical ratio ≥10th percentile (odds ratio, 6.1; 95% confidence interval, 3.03-12.75). A cerebroumbilical ratio >90th percentile appears protective of cesarean section for fetal compromise (negative predictive value 100%).

CONCLUSION

The fetal cerebroumbilical ratio can identify fetuses at high and low risk of a subsequent diagnosis of intrapartum compromise, and may be used to risk stratify pregnancies before labor.

Fetal response to intrauterine stress

Many human infants are born inappropriately small as a result of stress suffered during intrauterine life. Acute reductions in oxygen delivery to fetal tissues have therefore been studied in animals so that insight can be obtained into the adaptive mechanisms that underlie human developmental abnormalities. It is now known that during moderate hypoxic stress fetal arterial blood pressure is variably increased while heart rate and cardiac output are depressed; blood volume is reduced but cardiac output is redistributed to spare the myocardium, brain and adrenal glands at the expense of most other organs. Also a greater fraction of oxygen-rich venous blood from the placenta is returned to the heart for distribution. Spared organs are those that grow disproportionately well in human asymmetrical intrauterine growth retardation (IUGR). These cardiovascular responses are not fully understood although elevated fetal plasma levels of catecholamines and a host of fetal hormones are undoubtedly important. Chemical sympathectomy does not abolish the blood flow redistribution phenomenon, which implies that autoregulatory effects may be responsible for some of the redistribution of blood flow. Fetal hypoxaemia and metabolic abnormalities are sequelae often found with human IUGR, suggesting placental exchange defects. IUGR placentas appear to have defective transport mechanisms for many nutrients. Animal studies suggest that the placenta will give priority to its own needs over those of the fetus, when necessary, to support its own growth and function.

Umbilical artery Doppler and umbilical cord pH at birth in small-for-gestational-age fetuses: valid estimate of their relationship

OBJECTIVE

To evaluate the relationship between umbilical artery pulsatility index and the umbilical cord pH in small-for-gestational-age fetuses.

METHODS

Data were collected from all pregnancies seen in our Fetal Surveillance Unit that underwent antenatal monitoring for being small-for-gestational-age beyond 24 weeks of pregnancy. A linear regression was used to analyse the effect of the umbilical artery pulsatility index (UAPI) and umbilical artery pH at birth, assessing interaction and controlling for clinically meaningful antenatal, Doppler, biophysical and perinatal variables.

RESULTS

A total of 117 pregnancies were included. According to the estimated model (which included all clinically significant confounders and statistically significant interactions), in cases with reactive cardiotography (CTG) a 1-unit increase in the UAPI resulted in a mean decrease of 0.021 (95% 0.05 to -0.005) units of umbilical artery pH at delivery. In the non-reactive CTG group a 1-unit increase in the UAPI resulted in a mean decrease of 0.02 (95% CI 0.059 to -0.019) units of umbilical artery pH at delivery. Finally, in fetuses with a pathological CTG a 1-unit increase in the UAPI resulted in a mean decrease of 0.149 (95% CI 0.107 to 0.19) units of umbilical artery pH at delivery.

CONCLUSIONS

The crude effect between umbilical artery velocimetry on umbilical artery pH at birth has to be interpreted with caution, since an important part of this effect is related to other factors that confound and modify the relationship. After controlling for confounders, it was only in fetuses with pathological CTG that the effect remained statistically significant.

Evaluation of the fetal coronary circulation

Prenatal ultrasound today allows the detailed study of small caliber vascular beds including the fetal coronary arteries and the coronary sinus. The coronary circulation is unique because of its critical role in myocardial metabolism and function and its ability to adapt in many fetal conditions. The ultrasound examination techniques for the evaluation of the fetal coronary circulation are presented. Evaluation of the coronary arteries is primarily achieved by color flow imaging and pulsed wave Doppler. Conditions such as fetal growth restriction, anemia, ductus arteriosus constriction and bradycardia are associated with evidence of enhanced coronary blood flow. These findings suggest that short-term autoregulation and long-term alterations in myocardial flow reserve are present in the human fetus. At present, examination of coronary sinus blood flow has limited clinical utility, while increases of the coronary sinus diameter or attenuation of coronary sinus dynamics may provide useful markers of abnormalities of central venous drainage. Abnormal vascular connections between the coronary arteries and the ventricular cavities may be observed in outflow tract obstructive cardiac lesions. In these conditions prenatal detection of coronary fistulae may have a potential impact on outcome and therefore counseling and perinatal management.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.

The new obstetrics: its integration into neonatal clinical practise, teaching and research

Most neonatologists have not yet incorporated into their teaching, clinical service and research the advances in high risk obstetrics particularly as it relates to fetal surveillance. This brief review emphasizes some of the "new obstetrics" from the viewpoint of perinatal medicine, particularly in terms of neonatal teaching and the design of future neonatal research. The information that can be obtained about an infant prenatally by the use of ultrasound. power doppler, computerized fetal heart rate monitoring, cordocentesis, etc is extensive and yet, has rarely been utilized in the design of neonatal research protocols. It is becoming imperative that the "new obstetrics" be recognized and utilized in modern neonatal thinking if a truly "perinatal medicine" is to be practised.

Pathophysiology of intrauterine growth retardation: role of the placenta

The placenta is essential for normal fetal development. Failure of the placenta can result in many fetal conditions, for example, intrauterine growth retardation (IUGR). Placentas from pregnancies complicated by IUGR show vascular damage, which may lead to the onset of pregnancy-induced maternal hypertension. Accurate placental assessment may, therefore, indicate which fetuses are at risk of IUGR and so improve clinical evaluation and management of both the fetus and the mother. Placental development and function can be assessed by a number of methods, including measurement of placental weight at mid-gestation (placental growth in the second trimester correlates strongly with placental weight at birth), assessment of fetal and placental circulation (an association between perinatal morbidity and abnormal blood velocity profiles has been established) and assessment of placental metabolism and nutritional transfer (a reduction in transfer of nutrients may be an early indicator of IUGR.

Fetal placental embolization in the late-gestation ovine fetus: alterations in umbilical blood flow and fetal heart rate patterns

OBJECTIVE

Our goal was to determine the effect of chronic and acute umbilical-placental embolization on placental hemodynamic and fetal heart rate patterns in relation to fetal oxygenation in the near-term ovine fetus.

STUDY DESIGN

Daily fetal placental embolization was performed during 10 days in 9 sheep fetuses until fetal arterial oxygen content decreased by approximately 30%. Nine control fetuses received saline solution. Mean and pulsatile umbilical blood flow, perfusion pressure, placental vascular resistance, fundamental impedance, pressure pulsatility index, and umbilical artery resistance index corrected to a fetal heart rate of 160 beats/min were measured. On day 10 both groups were acutely embolized until fetal arterial pH decreased to approximately 7.00. Fetal heart rate was measured with the Sonicaid System 8000 (Oxford Sonicaid, Oxford, United Kingdom).

RESULTS

Chronic fetal placental embolization was associated with a progressive reduction in umbilical blood flow (p < 0.00001) and fetal arterial oxygen content (p < 0.001) whereas fetal heart rate patterns remained unaltered. A chronic increase in umbilical artery resistance index corrected to a fetal heart rate of 160 beats/min could be entirely explained only if the changes in umbilical artery pressure pulsatility index and the fundamental impedance were taken into account, in addition to the changes observed in placental vascular resistance. During acute embolization leading to a 50% reduction in umbilical blood flow (p < 0.0002) and a three times increase in placental vascular resistance (p < 0.0001), the most consistent change in fetal heart rate patterns related to progressive metabolic acidosis was an 84% decrease in absolute acceleration frequency (p < 0.0001) whereas short-term fetal heart rate variability remained unaltered.

CONCLUSION

Changes in umbilical artery resistance index induced by chronic umbilical-placental embolization resulting in fetal hypoxemia occurred before any changes in fetal heart rate patterns were detectable. A decrease in the absolute acceleration frequency was the only component of fetal heart rate patterns related to progressive metabolic acidosis in the near-term ovine fetus.

The effect of acute volume expansion and vasodilatation with verapamil on uterine and umbilical artery Doppler indices in severe preeclampsia

Preeclampsia is associated with increased peripheral, uterine, and umbilical artery resistance. Acute blood pressure reduction may result in shunting of blood and sudden fetal distress. We therefore investigated the effects of volume expansion and verapamil therapy on uteroplacental and umbilical resistance during treatment of preeclampsia.

MATERIALS AND METHODS

Five severe preeclamptics underwent volume expansion and subsequent vasodilatation with an infusion of verapamil. Invasive hemodynamic monitoring and Doppler ultrasonography were used to study changes in maternal, uterine, and umbilical hemodynamics.

RESULTS

Volume expansion and subsequent verapamil therapy was associated with significant changes in maternal hemodynamics without significant change in uteroplacental or umbilical resistance. Uterine artery waveform changes were noted, with disappearance of notching in some cases.

CONCLUSIONS

Volume expansion and verapamil therapy effectively reduces maternal blood pressure in preeclampsia, without adversely affecting uteroplacental or umbilical artery resistance. Uterine artery waveform changes may be associated with improved fetal outcome.

CK-BB as indicator of prenatal brain-cell injury in fetuses with absent or reverse end-diastolic flow velocities of the umbilical arteries

The purpose of this study is to determine the levels of brain type isoenzyme of creatine kinase (CK-BB) as a possible indicator of a pre-existing intrauterine brain-cell damage in cord blood sera of fetuses with preceding absent or reverse end-diastolic flow velocities of the umbilical arteries (AREDFV). CK-BB isoenzyme activities were determined in umbilical cord sera of 13 newborn infants with preceding AREDFV and in 14 fetuses with low end-diastolic flow velocities (LEDFV) of the umbilical arteries. 50 newborn infants with elective cesarean section and normal umbilical artery blood flow velocity waveforms were used as controls. Two-tailed Student's t-test and Fischer's exact test were used for statistical evaluation of the results. CK-BB isoenzyme activity did not depend on gestational age. Fetuses with AREDFV showed a significant increase in CK-BB values, whereas fetuses with LEDFV had CK-BB activities within the normal range of the controls. The elevated CK-BB values of the AREDFV group were not correlated with fetal acidosis at birth. Brain-cell injury with leakage of CK-BB isoenzyme might be present in fetuses with AREDFV even before (preterm) delivery.

Umbilical artery Doppler flow-velocity waveforms and fetal acid-base balance in Rhesus-isoimmunized pregnancies

Pulsed Doppler blood-flow velocity waveforms in the umbilical arteries, as well as blood gases, hematocrit, and lactate concentration in umbilical venous blood, were examined in 21 patients undergoing 49 cordocentesis, 34 of which were followed by fetal blood transfusion into the umbilical vein. The aim of the study was to evaluate the correlations, if any, between the Doppler indices from the umbilical artery (pulsatility index, resistance index, systolic/diastolic ratio) and the blood gas values (pO2, pCO2, O2 content, pH) and lactate content in the umbilical vein. The only correlation confirmed in this study was in the subgroup of anemic fetuses undergoing fetal blood transfusion, where correlation existed between A/B and the initial O2 content (r = -0.41, p < 0.02). We conclude that, in Rhesus-isoimmunized pregnancies, in contrast to other pregnancies, a close correlation does not exist between the Doppler indices in the umbilical artery and the fetal blood gas values.

Relationship between the fetal biophysical profile score, umbilical artery Doppler velocimetry, and fetal blood acid-base status determined by cordocentesis

OBJECTIVE

Fetal hypoxia-acidosis is part of the terminal pathway leading to intrauterine fetal death. A central premise of antepartum surveillance is that identification and timely delivery of the hypoxic or acidotic fetus will prevent intrauterine death and decrease long-term neurologic damage. The optimal method to identify fetal hypoxia-acidosis has not been determined. We attempted to compare the performance of the biophysical profile score and umbilical artery Doppler velocimetry in the identification of fetal acidemia, hypoxemia, and hypercarbia as determined by pH and gas analysis of fetal blood obtained by cordocentesis.

STUDY DESIGN

Fetal biophysical profile and umbilical artery Doppler velocimetry studies were performed before cordocentesis in 24 patients (26 to 40 weeks). Umbilical vein pH and blood gas values were determined in all cases. The pulsatility index of the umbilical artery was obtained with pulsed Doppler equipment. Receiver-operator characteristic curve analysis and stepwise multiple logistic regression were performed to examine the relationship between biophysical profile score, umbilical artery Doppler velocimetry, and acid-base status.

RESULTS

The prevalence of fetal acidemia (pH 2 SD below the mean for gestational age) was 41.7% (10/24). There was a significant relationship between the change in umbilical artery pulsatility index and fetal acidemia (chi 2 = 26.6, p < 0.001) and hypercarbia (chi 2 = 22.9, p < 0.001), but not hypoxemia (chi 2 = 1.0, p > 0.1), and between the biophysical profile score and fetal acidemia (chi 2 = 11.1, p < 0.001) and hypercarbia (chi 2 = 9.0, p < 0.005), but not hypoxemia (chi 2 = 2.3, p > 0.1). Stepwise multiple logistic regression demonstrated that umbilical artery Doppler velocimetry was a better explanatory variable for acidemia and hypercarbia than the biophysical profile score.

CONCLUSION

A strong relationship between the degree of fetal acidemia and hypercarbia and the results of umbilical artery Doppler velocimetry and biophysical profile was found. However, umbilical artery Doppler velocimetry was a better explanatory variable for these outcome than the biophysical profile score.

Diagnostic value of blood sampling in fetuses with growth retardation

BACKGROUND

Fetuses with intrauterine growth retardation are delivered if they have evidence of distress, as manifested by abnormalities in the fetal heart rate and umbilical-artery blood flow. We studied whether umbilical-blood sampling might provide further information useful for management.

METHODS

We measured hemoglobin and lactate concentrations, oxygen content, pH, blood gas levels, and base deficit in umbilical-vein blood and correlated these measurements with the heart rate and umbilical-artery wave forms recorded by Doppler velocimetry in 56 fetuses with growth retardation. Twenty-one fetuses had normal heart rates and normal results of velocimetry, 24 had normal heart rates and abnormal results of velocimetry (indicative of decreased diastolic flow), and 11 had abnormal heart rates and abnormal results of velocimetry.

RESULTS

None of the 21 fetuses with normal heart rates and velocimetry had hypoxia or acidemia. Of the 24 fetuses with normal heart rates and abnormal velocimetry, 4 (17 percent) had moderate lactic acidosis, 1 (4 percent) had a low pH value, and 3 (12 percent) had hypoxia. Of the 11 fetuses with abnormal heart rates and velocimetry, 7 (64 percent) had lactic acidosis, low blood oxygen content, and low pH values. The absence of end-diastolic flow increased the risk of hypoxia and acidemia. The proportion of fetuses with elevated hemoglobin concentrations was similar among the three groups.

CONCLUSIONS

Assessment of fetal oxygenation and acid-base balance is not indicated in fetuses with growth retardation if their heart rates and the results of velocimetry are normal. If the results of velocimetry are abnormal, fetal-blood sampling can distinguish fetuses that have growth retardation alone from those that also have hypoxia and acidosis, and thus may aid in determining the optimal time of delivery.

Relationship between fetal cardiac and extra-cardiac Doppler flow velocity waveforms and neonatal outcome in intrauterine growth retardation

In a total of 42 consecutive pregnancies with intrauterine growth retardation (IUGR), Doppler velocimetry was related to neonatal outcome as determined by Apgar score at 1 min, umbilical artery acid-base status and PO2, number of nucleated red blood cells (NRBC), duration of ventilatory support, and sonographic appearance of cerebral leukomalacia. Doppler flow velocity waveforms were obtained from the ascending aorta (AO), pulmonary artery (PA), internal carotid artery (ICA) and umbilical artery (UA) at 2-3 day intervals until delivery. At cardiac level the peak systolic velocity (PSV) and time-averaged velocity (AV), and at peripheral level the pulsatility index (PI) was determined. As all Doppler parameters were significantly related to gestational age at birth, gestational age was taken into account in the analysis. There was no relationship between Apgar score, acid-base status and Doppler parameters. Low AVAO was related to a low umbilical artery PO2. Significant correlations were established between PSVPA, AVPA and PIUA, and the duration of neonatal ventilatory support. Infants who died within 22 days after admission to the neonatal intensive care unit (n = 7) displayed a significantly higher PIUA than those who remained alive. The PIUA was also related to the absolute and relative number of NRBCs. No relationship existed between the Doppler parameters and degree of leukomalacia. The present study demonstrates that from all Doppler parameters, the PIUA is most clearly related to neonatal outcome in IUGR.

The current status of maternal and fetal blood flow velocimetry

Significant progress has been achieved in regard to normative data for uteroplacental and fetal blood flow velocity and the factors which may affect these observations. Associations have been demonstrated between abnormal indices of maternal and fetal blood flow velocity and pregnancy-induced hypertension, fetal growth retardation, fetal blood gas measures, and intrapartum clinical fetal distress. However, in general, the predictive power is modest and no evidence has yet been provided to indicate that these measures can be used as a screening test in the general obstetric population. Continuing research is highly desirable. At the present time, the use of Doppler assessment of blood flow in pregnancy should be limited to the investigational setting.

Doppler velocimetry: critical analysis of umbilical, cerebral and aortic reference values

Cross-sectional reference standards of the umbilical flow velocity waveforms were investigated from 18 to 38 weeks of gestation on 482 normal pregnancies. A significant decrease in the pulsatility index (PI) and systolic/diastolic (SD) ratio was observed during gestation. This phenomenon was confirmed in a longitudinal study on 150 patients of the same population. The two slopes of cross-sectional and longitudinal data were not significantly different. A bimodal distribution of PI and S/D ratio was observed. Six per cent of data fell above the vast majority of cases. The dimension of the population studied allowed us to consider these findings not as outliers but as an interesting transient phenomenon of very low end-diastolic velocities which can occur in normal fetuses, without concomitant variations on the thoracic aorta and middle cerebral artery. Cross-sectional reference ranges were studied for these vessels on the same population from 26 to 38 weeks of gestation. A significant decrease in the PI of the middle cerebral artery was observed versus a significant increase in the PI of the thoracic aorta. These latter indices could be used to obtain indirect information on the normal redistribution of blood flow in the human fetus in the third trimester of gestation. However, the great variability observed should warn against the risks of a simplistic clinical use of these observations.

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.

Doppler assessment of the fetal and uteroplacental circulation during nifedipine therapy for preterm labor

To investigate the effects of nifedipine on the human fetal circulation, 11 fetuses whose mothers were treated with nifedipine for treatment of preterm labor were studied. Maximum velocity waveforms were obtained in the middle cerebral artery (n = 8), renal artery (n = 6), ductus arteriosus (n = 8), and umbilical artery (n = 10). Transvalvular maximal velocity waveforms were obtained across the aortic (n = 11) and pulmonary (n = 7) valves. Maternal uterine arteries also were studied (n = 7). Doppler data were collected before and 5 hours after nifedipine therapy. Patients received an oral loading dose of 30 mg of nifedipine followed by a second oral dose of 20 mg 4 hours later. No significant difference in the flow velocity waveforms was found in the vessels studied 5 hours after the initial dose. These results suggest that short-term nifedipine therapy does not influence either fetal or uteroplacental circulation as evaluated with the Doppler technique.

Umbilical flow waveforms versus fetal biophysical profile in hypertensive pregnancies

The pulsatility index (PI) of the umbilical arteries was measured in 40 hypertensive pregnancies. Doppler-velocimetric data were kept unknown to the clinical staff. An abnormal PI was found in 79% of cases in which an abnormal fetal growth in utero had been diagnosed by ultrasonographic measurements. Serial PI findings showed worsening figures in most of the cases with an abnormal fetal growth, irrespective of the last absolute value. Amniotic fluid estimation and PI data were significantly correlated. PI values were markedly abnormal in fetuses with non-reactive heart-rate tracings. A high sensitivity and an optimal specificity were found for umbilical PI versus the diagnosis of fetal growth retardation made by the coexistence of different biophysical criteria. However, false normal results may occur. 62% of the newborns weighed below the 5th percentile. The sensitivity of abnormal PI values to detect these light fetuses resulted to be only 67%. However the prevalence of neonatal morbidity in fetuses with abnormal PI values was 74%, while morbidity occurred only in 14% of cases with normal PI values. In hypertensive pregnancies, this simple velocimetric parameter proved to correlate with abnormal biophysical monitoring and complicated neonatal outcomes.

Screening with Doppler velocimetry in labor

Doppler flow velocimetry was performed on 273 nonselected patients in labor. All patients were at least 2 cm dilated and 80% effaced (58% greater than 4 cm) and were delivered of infants within 24 hours. Fetal heart rate tracing performed at the same time was read by another observer and compared with Doppler flow velocity measurements (systolic/diastolic ratio, pulsatility index). A significant correlation was noted (r = 0.234, p less than 0.001) between the two modalities. Both fetal heart rate tracings and umbilical flow velocity measurements were correlated with fetal outcome. Significant associations were noted between the umbilical systolic/diastolic ratio and fetal distress. 5-minute Apgar scores, the need for intubation independent of gestational age, and umbilical arterial cord pH and base excess. It appears that the information obtained from flow velocimetry had additional benefits compared with that of fetal heart rate tracings alone.