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.     

Fetal umbilical artery velocity waveforms and subsequent neonatal outcome

Flow velocity waveforms (FVWs) from the fetal umbilical artery were recorded from 2178 pregnant women over a 6-year period. All of them had an obstetric factor indicating increased risk of fetal compromise. A total of 6749 studies was recorded. The systolic diastolic (AB) ratio was measured and classified as normal (less than 95th centile), elevated (95-99th centile), high (greater than 99th centile) or extreme (absent diastolic flow). The results of these studies have been related to subsequent fetal and neonatal outcome. An abnormal umbilical artery FVW was associated with shorter gestation and infants with lower birthweight, shorter length and lower ponderal index. There was a highly significant association between an abnormal FVW and the birth of an infant small for gestational age. The significance of the association increased with the increased abnormality of the umbilical artery FVW and this was independent of gestational age. Preterm infants associated with high or extreme AB ratios spent twice as long in the neonatal nursery than those with normal AB ratios. Analysis of 794 pregnancies studies serially indicated that an abnormal FVW in which the AB ratio was increasing, in contrast to a decreasing AB ratio, predicted a poor outcome for both size at birth and duration of neonatal intensive care. We conclude that in high risk pregnancy Doppler umbilical artery FVW studies predict the most compromised fetuses in terms of growth retardation and requirements for neonatal intensive care.     

Fetal umbilical artery velocity waveforms and subsequent neonatal outcome

Summary. Flow velocity waveforms (FVWs) from the fetal umbilical artery were recorded from 2178 pregnant women over a 6-year period. All of them had an obstetric factor indicating increased risk of fetal compromise. A total of 6749 studies was recorded. The systolic diastolic (AB) ratio was measured and classified as normal (<95th centile), elevated (95–99th centile), high (>99th centile) or extreme (absent diastolic flow). The results of these studies have been related to subsequent fetal and neonatal outcome. An abnormal umbilical artery FVW was associated with shorter gestation and infants with lower birthweight, shorter length and lower ponderal index. There was a highly significant association between an abnormal FVW and the birth of an infant small for gestational age. The significance of the association increased with the increased abnormality of the umbilical artery FVW and this was independent of gestational age. Preterm infants associated with high or extreme AB ratios spent twice as long in the neonatal nursery than those with normal AB ratios. Analysis of 794 pregnancies studies serially indicated that an abnormal FVW in which the AB ratio was increasing, in contrast to a decreasing AB ratio, predicted a poor outcome for both size at birth and duration of neonatal intensive care. We conclude that in high risk pregnancy Doppler umbilical artery FVW studies predict the most compromised fetuses in terms of growth retardation and requirements for neonatal intensive care.     

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.     

Umbilical artery Doppler flow velocimetry in intrauterine growth restriction and its relation to perinatal outcome.

OBJECTIVE: The purpose of this retrospective analysis was to compare pregnancy outcomes in growth-restricted fetuses retaining normal umbilical artery Doppler flow and the outcomes of pregnancies with end-diastolic velocity either diminished or severely reduced/absent. METHODS: One hundred pregnant women with growth-restricted fetuses were followed with Doppler velocimetry of the umbilical artery between weeks 28 and 41 of pregnancy. Outcomes were compared for the normal Doppler group (16%), the less-severely abnormal group (77%), and the group with severely reduced or absent end-diastolic velocity waveforms (7%). RESULTS: The diagnosis-to-delivery interval was significantly shorter, and the average birth weight and gestational age at delivery were significantly lower, for fetuses with abnormal Doppler velocimetry (showing diminished or severely reduced/absent end-diastolic velocity) than for those in the normal Doppler group. Fetuses with abnormal Doppler velocimetry also had a significantly higher incidence of oligohydramnios, low-birth weight (<10th percentile), and admission to the Neonatal Intensive Care Unit. There were no perinatal deaths among the normal Doppler patients. CONCLUSIONS: Growth-restricted fetuses with normal umbilical artery velocimetry are at significantly lower risk than those with abnormal velocity waveforms, and immediate delivery of the fetus with diminished end-diastolic flow may be unnecessary. Knowing this relationship may be useful in the clinical management of such pregnancies. Doppler surveillance of growth-restricted fetuses supplemented with cardiotocography, preferably combined with biophysical profile testing, results in a prolonged gestational age and acceptable fetal outcome.     

Umbilical artery velocity waveforms: poor association with small-for-gestational-age babies

A total of 205 high-risk pregnancies was studied using continuous wave Doppler ultrasound examination of the umbilical artery to investigate the ability of the test to detect small-for-gestational-age (SGA) infants. The waveforms were analysed by calculating a ratio of the peak systolic to end diastolic frequency (A/B ratio). An A/B ratio greater than 95th centile from our derived normal values was classified as abnormal. Three outcome variables were examined: birthweight for gestational age, the standard deviation birthweight score and the ponderal index. Although of the 56 pregnancies with an abnormal Doppler result 34 (61%) were associated with a SGA infant, only 41% of all the SGA infants had an abnormal Doppler result. Alternative measures of growth, the ponderal index and the SD birthweight score, showed that on average the babies in the Doppler abnormal group were smaller than those in the Doppler normal group, but the overlap between the normal and abnormal groups was large. Therefore although Doppler ultrasound appears to identify groups of smaller babies, it does not identify individual pregnancies where the baby will be small at birth.     

Umbilical artery velocity waveforms: poor association with small-for-gestational-age babies

Summary. A total of 205 high-risk pregnancies was studied using coninuous wave Doppler ultrasound examination of the umbilical artery to investigate the ability of the test to detect small-for-gestational-age (SGA) infants. The waveforms were analysed by calculating a ratio of the peak systolic to end diastolic frequency (A/B ratio). An A/B ratio >95th centile from our derived normal values was classified as abnormal. Three outcome variables were examined: birthweight for gestational age, the standard deviation birthweight score and the ponderal index. Although of the 56 pregnancies with an abnormal Doppler result 34 (61 %) were associated with a SGA infant, only 41% of all the SGA infants had an abnormal Doppler result. Alternative measures of growth, the ponderal index and the SD birthweight score, showed that on average the babies in the Doppler abnormal group were smaller than those in the Doppler normal group, but the overlap between the normal and abnormal groups was large. Therefore although Doppler ultrasound appears to identify groups of smaller babies, it does not identify individual pregnancies where the baby will be small at birth.     

Flow velocity waveforms in the maternal uteroplacental and fetal umbilical placental circulations

A simple continuous-wave Doppler ultrasound system was used to record arterial flow velocity time waveforms from branches of the maternal uterine artery in the placental bed and the fetal umbilical arteries. The systolic-diastolic ratio of flow velocities was measured as an index of peripheral resistance. In normal pregnancy both circulations exhibit high diastolic flow velocities caused by low resistance. The study group consisted of 172 pregnancies with high fetal risk of which 53 resulted in delivery of a small-for-gestational age infant. The last study-to-delivery interval was less than 10 days. In the small-for-gestational age fetuses in whom both umbilical and uterine studies were normal there was good fetal outcome (19 cases). Neonatal morbidity occurred among those with abnormal umbilical studies with low diastolic flow velocities, indicating high resistance. Of these studies there were two subgroups. An abnormal uterine study (13 cases) indicated a primary maternal uteroplacental lesion and a normal study (21 cases) a primary fetal lesion. In cases of severe maternal hypertension, abnormal uterine artery waveforms were associated with abnormal umbilical artery waveforms.     

A comparative study of fetal umbilical velocimetry with continuous- and pulsed-wave Doppler ultrasonography in high-risk pregnancies: relationship to outcome

Systolic/diastolic ratios of umbilical velocimetry obtained with either continuous-wave or pulsed-wave Doppler ultrasonography have been used to assess downstream placental vascular resistance and fetal well-being. The purpose of this study is to compare the efficacy of systolic/diastolic ratios obtained by continuous-wave and pulsed-wave Doppler ultrasonography in the prediction of poor pregnancy outcome. Continuous-wave and pulsed-wave umbilical velocimetry was performed and systolic/diastolic ratios were measured in 200 high-risk pregnancies in the third trimester by use of Angioscan III and a General Electric RT 3600 scanner, respectively. A total of 165 study participants had normal systolic/diastolic ratios and 35 participants had elevated ratios (greater than 3.0) with both continuous-wave and pulsed-wave Doppler ultrasonography. Both methods identified 35 participants with abnormal ratios, and none of the women was misclassified by either method. The pulsed-wave and continuous-wave values for 35 participants with elevated ratios were 6.35 +/- 1.52 and 6.23 +/- 1.58, respectively; values for 165 participants with normal ratios were 1.95 +/- 0.40 and 1.96 +/- 0.41, respectively (not significantly different). Participants with elevated systolic/diastolic ratios within 7 days of delivery had significantly higher incidence of adverse pregnancy outcome as judged by small-for-gestational-age fetuses, presence of meconium at delivery, fetal distress in labor, cesarean sections and 5-minute Apgar scores less than 7. Fetuses with elevated ratios were delivered at an earlier gestational age (34 +/- 1.2 weeks), had lower birth weights (1422 +/- 151 gm), and spent more time in the neonatal intensive care unit (17.1 +/- 5.2 days), compared with fetuses with normal ratios (delivered at 38.5 weeks +/- 0.9 weeks, 3100 +/- 210 gm birth weights, and 2 +/- 0.2 days spent in neonatal intensive care units, respectively, p less than 0.05). We therefore conclude that continuous-wave and pulsed-wave Doppler ultrasonography produce similar results with regard to systolic/diastolic ratios in high-risk pregnancies, and either method appears to be a valuable adjunct in the surveillance of high-risk pregnancies.     

Umbilical and uterine artery flow velocity waveforms in pregnancy associated with major fetal abnormality

Flow velocity waveforms from the umbilical artery and branches of the uterine artery in the placental bed were recorded using continuous wave Doppler ultrasound. The records of 26 patients with pregnancy complicated by major fetal abnormality were reviewed to determine the changes of a primary fetal disturbance. The systolic/diastolic (A/B) ratio was used as an index of blood flow resistance. In 13 of the 26 patients the umbilical artery waveform systolic/diastolic ratio was high. It is postulated that in these patients there is a process of obliteration of small arteries in the placenta that is triggered by the abnormal fetus. In all patients the uterine artery waveform was normal. In seven of these 13 patients the infant had a birthweight greater than 10th centile. Placental weights were examined. A small placenta expressed as either low weight for gestational age or low placental/fetal weight ratio was associated with a normal umbilical artery waveform. It is suggested that fetuses in these groups have a low growth potential. In contrast a high placental/fetal weight ratio was associated with an abnormal umbilical artery waveform pattern.     

Umbilical and uterine artery flow velocity waveforms in pregnancy associated with major fetal abnormality

Summary. Flow velocity waveforms from the umbilical artery and branches of the uterine artery in the placental bed were recorded using continuous wave Doppler ultrasound. The records of 26 patients with pregnancy complicated by major fetal abnormality were reviewed to determine the changes of a primary fetal disturbance. The systolic/diastolic (A/B) ratio was used as an index of blood flow resistance. In 13 of the 26 patients the umbilical artery waveform systolic/diastolic ratio was high. It is postulated that in these patients there is a process of obliteration of small arteries in the placenta that is triggered by the abnormal fetus. In all patients the uterine artery waveform was normal. In seven of these 13 patients the infant had a birthweight > 10th centile. Placental weights were examined. A small placenta expressed as either low weight for gestational age or low placental/feta1 weight ratio was associated with a normal umbilical artery waveform. It is suggested that fetuses in these groups have a low growth potential. In contrast a high placental/fetal weight ratio was associated with an abnormal umbilical artery waveform pattern.     

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.     

Doppler Flow Velocity Waveform Analysis in Postdate Pregnancies

This study examines the efficiency of Doppler flow velocity waveform analysis in the evaluation of the postdate pregnancy. Seventy women whose pregnancies were at or beyond 41 weeks' gestation were assessed by calculating the systolic/diastolic ratios from umbilical and uteroplacental arteries. Waveform ratios from pregnancies associated with fetal compromise and abnormal neonatal outcome were similar to those from pregnancies in which the outcome was normal. These findings indicate that the pathophysiology of placental insufficiency in postdate pregnancies differs from that observed in cases of fetal growth retardation at earlier gestational ages. Doppler flow velocity waveform analysis is unlikely to be of benefit in the routine assessment of the postdate pregnancy.     

Umbilical artery waveforms in triplet and quadruplet pregnancies.

The incidence of abnormal umbilical waveforms in triplet and quadruplet pregnancies and its correlation with adverse pregnancy outcome was studied by a retrospective review of all our triplet and quadruplet pregnancies (1986-1993) with documented Doppler flow assessment. Obstetrical outcomes were analyzed in relation to abnormal umbilical artery waveforms. Nineteen triplet and 4 quadruplet pregnancies were studied. Of 73 fetuses, 6 had abnormal umbilical artery waveforms (8.2%). All abnormal waveforms were characterized by persistent absence of the end-diastolic velocities (AEDV). In comparing the abnormal and normal groups, significant differences were found in birth weights (910+/-433 vs. 1,724+/-434 g; p = 0.0004), small for gestational age rate [5/6 (83%) vs. 5/67 (7.5%); p = 0.0003], and perinatal mortality rate [3/6 (50%) vs. 2/67(3%); p = 0.001]. There were no differences in congenital anomalies, gestational age at birth, and neonatal intensive care admission. In conclusion, it seems that Doppler umbilical artery waveforms in multiple pregnancies were either normal or extremely abnormal (e.g. AEDV). AEDV was associated with adverse perinatal outcomes such as low birth weight, growth restriction and perinatal mortality.     

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.     

Prediction of pre-eclampsia, low birthweight for gestation and prematurity by uterine artery blood flow velocity waveforms analysis in low risk nulliparous women

Objective To assess the performance of four previously reported Doppler abnormalities of uterine artery velocity waveforms (presence of a protodiastolic notch, peak systolic over protodiastolic velocities (A:C ratio) > 2.5, peak systolic over end diastolic velocities (A:B ratio) > 90th centile, resistance index (RI) ([A-B]/A) ≥0.58) in predicting pre-eclampsia, low birthweight and prematurity.
Design Prospective cohort study.
Setting Tertiary care university hospital in Quebec City.
Population 1311 nulliparous women.
Methods Evaluation of pulsed Doppler abnormalities of uterine artery velocity waveforms was carried out in 1000 and 1 194 of women at 18.3 (SD 0.9) or 26.7 (SD 0.9) weeks of pregnancy.
Main outcome measures Pre-eclampsia, birthweight below the 10th centile for gestational age and spontaneous preterm birth (< 37 completed gestation weeks).
Results Pre-eclampsia, low birthweight for gestation and prematurity occured in 4%, 11% and 7% of the pregnancies, respectively. At 26 weeks all the abnormalities of the studied Doppler indices were significantly associated with pre-eclampsia and low birthweight for gestation as reflected by the 95% confidence intervals of the positive likelihood ratios which did not include the value 1. However, sensitivities (26% to 34%) and positive predictive values (7% to 28%) were low. No Doppler indices performed significantly better than the others. The abnormalities of the Doppler indices were not associated with spontaneous prematurity. The performance of the Doppler measurements performed at 18 weeks was poor.
Conclusions Uterine artery Doppler velocimetry waveform analysis does not qualify as a reliable screening test for pre-eclampsia or low birthweight for gestation in low risk pregnancies but may be useful in selected high risk populations.     

Middle cerebral artery to umbilical artery resistance index ratio in the prediction of neonatal outcome.

OBJECTIVE: The objectives of this study were to evaluate the usefulness of the middle cerebral artery to umbilical artery resistance index ratio (C/U ratio) as a predictor of adverse perinatal outcome, and to show that the absence of fetal umbilical artery end-diastolic velocity (AEDV) in SGA fetuses is associated with high morbidity and mortality. METHOD: In this prospective study, color Doppler flow imaging was used for the estimation of the C/U ratio in fetuses that were small for their gestational age, in 70 singleton pregnancies between 29 and 42 weeks of gestation. The subjects were categorized into two groups, with Group A consisting of 35 small for gestational age (SGA) fetuses with a normal C/U ratio (1.05 or higher), and Group B comprising 35 SGA fetuses with an abnormal C/U ratio (below 1.05). RESULT: The mean C/U ratio values for birth weight and gestational age were higher in group A than in group B. Fetuses born to mothers in group B stayed longer in the neonatal special care unit (NSCU), whereas the period from ultrasound examination to delivery was higher in the cases in group A. A higher percentage of mothers with an abnormal C/U ratio underwent cesarean section. Fetuses with an absent end-diastolic velocity of the umbilical artery had a higher morbidity. Three stillbirths occurred in fetuses with an absent end-diastolic velocity of the umbilical artery. CONCLUSION: Our results suggest that the C/U ratio is a good predictor of neonatal outcome, and could be used to identify fetuses at risk of morbidity and mortality. Fetal umbilical artery AEDV with intrauterine growth restriction is associated with high perinatal morbidity and mortality.     

Uteroplacental blood flow velocity-time waveforms in normal and complicated pregnancy

Summary. A simple continuous wave Doppler ultrasound system for recording arterial flow velocity waveforms in branches of the uterine artery in the placental bed is described. Twelve normal pregnancies were studied serially from 20 weeks to delivery. The diastolic flow velocity expressed as a percentage of the systolic provides an index of downstream vascular bed resistance and perfusion. This always exceeded 50% in normal pregnancy and there was a small increase with gestational age indicative of a decreasing flow resistance. Of the 91 complicated pregnancies, studied because of potential uteroplacental insufficiency and fetal risk, 25 resulted in the birth of an infant small-for-gestational-age. In 15 the uterine artery flow velocity waveform revealed a pattern of low diastolic flow velocity. It is postulated that these represent a subgroup of growth-retarded fetuses in whom there is reduced uterine artery perfusion. Reduced uterine artery diastolic flow velocity in these patients was associated with reduced umbilical artery diastolic flow velocity on the fetal side of the placenta. In contrast the 10 small-for-gestation infants associated with normal uterine artery waveforms suggest a primary fetal cause. Twelve patients with severe hypertensive disease of pregnancy were studied. Nine were associated with reduced uterine artery diastolic flow velocity (reduced uterine artery perfusion) consistent with vasospasm in the branches of the uterine artery in the placental bed.     

An evaluation of the efficacy of Doppler flow velocity waveform analysis as a screening test in pregnancy

In a prospective double-blind study of 535 medium-risk pregnancies, growth data obtained by ultrasonography and Doppler flow velocity waveform systolic to diastolic ratios were recorded at 18, 24, 28, and 34 weeks' gestation. A significant association was observed between uteroplacental systolic to diastolic ratios at 24 weeks' gestation and subsequent fetal hypoxia with a sensitivity of 24.0% and a specificity of 93.9%. However, 70% of abnormal results were not followed by fetal hypoxia. Umbilical artery systolic to diastolic ratios at 24, 28, and 34 weeks' gestation were found to be predictive of intrauterine growth retardation. This predictive capability was enhanced in those growth-retarded fetuses in which hypoxia developed, but was weak when umbilical artery systolic to diastolic ratios were evaluated as primary screening tests for fetal hypoxia. The results confirm a role for Doppler systolic to diastolic ratios in the evaluation of high-risk pregnancies but do not support a role for their use as primary screening tests in low-risk obstetric populations.