Fetal and maternal Doppler flow velocity waveforms in normal sheep pregnancy

Abnormalities in placental vascular resistance have been shown to have an important association with intrauterine growth retardation in both human and sheep pregnancies. In this study we have assessed impedance to blood flow through the ovine placental circulation by Doppler flow velocity waveform analysis. As gestation advanced from 66 to 136 days, a significant decrease in impedance to flow was observed in both umbilical and maternal placental arteries. The greatest decrease in impedance was observed between 66 and 109 days' gestation in umbilical arteries and between 66 and 80 days' gestation in maternal placental arteries. In these normal pregnancies, no significant correlations could be found between Doppler flow velocity waveform analyses and fetal or placental growth. We conclude that Doppler flow velocity waveform analysis is a valuable and non-invasive method to assess impedance to blood flow through the placental circulation in pregnant sheep.     

Fetal blood velocity waveforms in normal pregnancies. A longitudinal study

Blood velocity in the umbilical artery, fetal descending aorta and fetal middle cerebral artery was recorded by means of 3.5 MHz pulsed Doppler ultrasound in 22 normal pregnancies. The measurements were performed longitudinally between 25 and 42 weeks of gestation. The maximum blood velocity curves were analysed for pulsatility index (PI), systolic/diastolic velocity ratio (S/D ratio) and in the middle cerebral artery also for the resistance index according to Pourcelot (RI). In the umbilical artery, all variables decreased significantly with increasing gestational age as an expression of the decreasing placental vascular resistance. PI in the descending aorta remained fairly constant during the examined period of gestation. In the middle cerebral artery, all three variables (PI, S/D ratio, RI) decreased significantly as gestation advanced. With the exception of the umbilical artery at 28-32 weeks, PI and S/D ratio were not influenced by the heart rate in any of the vessels examined. Diagrams of the gestational age-related reference values (means +/- 2 SD) for the variables of the blood velocity waveforms were established. Additionally, a ratio of the PI and S/D was calculated for the umbilical artery and middle cerebral artery.     

Fetal blood flow velocity waveforms as predictors of growth retardation

Seventy-five high-risk pregnancies were studied in order to define the clinical value of the analysis of fetal blood flow velocity waveforms in early screening for growth retardation. Recordings were obtained at 26-28 weeks' gestation, in the absence of ultrasonographic signs of growth retardation, using a pulsed duplex Doppler system. The pulsatility index was evaluated at the level of the umbilical artery, descending aorta, and internal carotid artery. Fetuses (N = 23) who developed growth retardation showed higher values of pulsatility index in the umbilical artery (P less than .001) and descending aorta (P less than .05) than fetuses of normal growth. In the internal carotid artery, the pulsatility index was lower (P less than .001) in the fetuses who developed growth retardation than in those with normal growth. The ratio between the pulsatility indexes of the umbilical and internal carotid arteries proved an accurate predictor of growth retardation (specificity 92.3%; sensitivity 78.2%; positive predictive value 81.8%; negative predictive value 90.5%; accuracy 88%).     

Umbilical artery blood flow velocity waveforms in pregnancy complicated by diabetes mellitus

Summary Umbilical artery blood velocity waveforms were recorded by a pulsed Doppler system in the third trimester of pregnancy in 16 diabetic women (12 class B, 1 class C, 3 class D) and the waveforms were analysed for resistance index (RI = peak systolic velocity minus end diastolic velocity/peak systolic velocity). There was no significant correlation between the RI values and either serum glucose (r=0.385) or fructosamine levels (r=0.380). However, the RI values were raised in two cases with serum glucose levels of over 300 mg/dl. With a fall in serum glucose levels, the RI values returned to the normal range. No abnormal umbilical artery velocity waveforms were found when the serum glucose level was below 200 mg/dl.     

Fetal atrioventricular and outflow tract flow velocity waveforms during normal second half of pregnancy

Maximum flow velocity waveforms at atrioventricular and outflow tract level were studied longitudinally in 40 fetuses from 18 to 38 weeks' gestation at 3- to 4-week intervals. Flow velocity parameters studied were peak systolic and time-averaged velocity and acceleration time at outflow tract level and time-averaged velocity, peak E-wave and peak A-wave velocities, and E/A ratio at atrioventricular level. An increase of all flow parameters with advancing gestational age was found. Aortic parameters were higher than pulmonary ones. Time-averaged, peak E-wave, and peak A-wave velocities were higher at tricuspid level than at mitral level, whereas E/A ratios were higher at mitral level. Outflow tract parameters showed no correlation with period time. A positive correlation for peak E-wave velocity and E/A ratio, and a negative correlation for time-averaged and peak A-wave velocity was found with period time. These results suggest that the normal second half of pregnancy is characterized by rising ventricular stroke volume and output and reduction in ventricular afterload. The left ventricular afterload seems to be lower than the right ventricular afterload. Atrioventricular flow velocities are heart rate dependent.     

Fetal umbilical and internal carotid artery blood flow velocity waveforms during maternal fenoterol administration

Blood flow velocity waveforms in the fetal umbilical and internal carotid artery were studied during maternal fenoterol treatment in 25 pregnant patients admitted for premature labour between 27 and 35 weeks of gestation. The pulsatility index (PI) from the umbilical artery was significantly reduced (p = 0.02), the PI being situated below the -2 SD limit of the normal reference curve in 28%. There was no statistically significant difference in PI from the umbilical artery when distinguishing between ruptured and unruptured membranes. The reduced pulsatility index of the umbilical artery suggests a decrease in vascular resistance, hence improved utero-placental perfusion. The pulsatility index of the fetal internal carotid artery followed the normal distribution.     

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.     

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 and uteroplacental flow velocity waveforms and placental grading

Doppler studies were performed on umbilical, fetal internal carotid, and arcuate arteries within 36 to 40 weeks of gestation in 85 women (66 with healthy pregnancies and 18 complicated by growth retardation, and results were analyzed by calculating the pulsatility index. In each case the placenta was examined and graded sonographically. No significant correlation was found between pulsatility index in fetal and uteroplacental vessels and placental grading in normal pregnancies. This suggests that tissue changes responsible for the echogenicity of maturing placenta are not directly related to vascular impedance of the placental vascular bed.     

脐血流值与高危妊娠结局及胎盘病理改变的关系

采用脉冲式多普勒测定１０１例高危妊娠的脐动脉（ＵｍＡ）收缩期最大血流速度（Ｓ）与舒张末期速度（Ｄ）的比值（ＵｍＡ Ｓ／Ｄ）；制作受试者工作曲线（ＲＯＣ曲线）；并对高危妊娠１９例，正常妊娠１０例妇女（Ａ组）进行ＵｍＡ Ｓ／Ｄ值与胎盘病理检查。结果显示：ＵｍＡ Ｓ／Ｄ值为２．８作为最佳临界点；该点预测高危妊娠不良结局的敏感性为７０．６％，特异性为９７．６％；高危妊娠妇女中，ＵｍＡ Ｓ／Ｄ＜２．８者９例     

Fetal internal carotid artery flow velocity time waveforms in twin pregnancies

The fetal internal carotid artery and umbilical artery flow velocity time waveforms were studied in 17 consecutive twin pregnancies. The pulsatility index was calculated for each fetus in each artery as an index of vascular resistance. All studies were done within 14 days before delivery. In 8 pregnancies both fetuses were of birthweight appropriate for gestational age; whereas, in 9 patients one or both of the infants were small for gestational age (SGA). From ultrasound criteria and Doppler studies of the umbilical and fetal internal carotid arteries, decreased fetal internal carotid artery pulsatility index (cut off value less than or equal to 1.2) was found to be the best predictor of SGA (sensitivity 83%, specificity 95%, positive predictive value 91%, negative predictive value 91%).     

Umbilical artery flow velocity waveforms and twin pregnancy outcome

Two hundred seventy-two twin pregnancies were studied by analysis of the fetal umbilical artery waveforms recorded using continuous-wave Doppler ultrasound. After the first 100 cases, a management strategy was adopted whereby all twin gestations would be studied between 28-32 weeks' gestation and the results made available to the referring obstetrician, thereby influencing clinical management. Perinatal mortality and morbidity, in pregnancies with both fetuses alive at 28 weeks' gestation, were compared between the patients studied in the first group of 100 and those studied after the Doppler examination was introduced as a clinical service. There was a decrease in perinatal mortality, both uncorrected (57.9 per 1000 to 17.9 per 1000; P less than .05) and corrected (42.1 per 1000 to 8.9 per 1000). Fetal deaths were reduced from six to one (P less than .05). This decrease in perinatal mortality was achieved without any appreciable change in the gestational age at delivery or mode of delivery between the two groups. There was a reduction in the number of infants requiring neonatal intensive care (from 38% to 24%; P less than .01).     

Renal arterial blood flow velocity waveforms in pregnant women

Seventy-two continuous-wave Doppler ultrasonographic examinations were performed on nine nonpregnant and 56 normal pregnant women. The range of gestation was 6 to 40 weeks, and the objective was to record the renal arterial blood flow velocity waveform. Acceleration time and systolic per diastolic ratio of renal arterial blood flow velocity waveforms were assessed. Of 72 examinations, 68 recordings were made of the left renal artery (94.4%) and 28 of the right renal artery (38.9%), respectively. There was no correlation between acceleration time and systolic per diastolic ratio and gestational age, respectively, and no correlation between acceleration time and systolic per diastolic ratio, and caliceal diameter of the renal pelvis, respectively. Acceleration times of the left and right renal arteries were 47 +/- 11 and 40 +/- 8 msec in nonpregnant women and 62 +/- 23 and 62 +/- 23 msec in pregnant women, respectively. The left and right systolic per diastolic ratios were 3.1 +/- 0.7 and 2.9 +/- 0.5 in nonpregnant women and 2.8 +/- 0.6 and 2.6 +/- 0.5 in pregnant women, respectively. Therefore these data provide a foundation for the study of hydronephrosis, which may occur in pregnant women.     

Fetal and uteroplacental flow velocity waveforms in the expectant management of placental abruption

The change in flow velocity waveforms was assessed by Doppler ultrasound in the course of evolution of placental separation. The velocity changes reflected a high response to blood flow in the placental circulation along with decreased cerebral vascular resistance.     

Nucleated red blood cells in uncomplicated prolonged pregnancy

OBJECTIVE: Elevated counts of nucleated red blood cells (NRBCs), as well as prolongation of pregnancy, have been suggested as predictors of adverse perinatal outcome. However, the association between these 2 variables has received only minimal attention. We sought to evaluate fetal NRBCs in prolonged pregnancies. METHODS: Umbilical cord blood was prospectively collected at delivery from 75 prolonged (at or beyond 287 days) pregnancies. One hundred and fifty term deliveries (260-286 days) served as controls. All pregnancies were accurately dated with the use of first-trimester sonography. Fetal biophysical profile testing was initiated at 40 weeks of gestation. Patients were delivered if they were in spontaneous labor or the biophysical profile was nonreassuring or by 42 weeks of gestation. Nucleated red blood cell counts were expressed per 100 white blood cells (WBC). Umbilical artery pH studies, as well as other demographic and clinical variables, were obtained. RESULTS: Prolonged pregnancy was associated with a significantly increased incidence of induction of labor and a greater birth weight. There were no other differences between the study group and controls. The median NRBCs per 100 WBCs in prolonged pregnancy was not significantly elevated over the term values (median 3, range 0-35 versus median 3, range 0-34, respectively; P =.25). Neonatal outcome was also comparable between groups. The univariate regression analysis demonstrated a significant association between elevated NRBC counts and low arterial cord blood pH (P <.008, R = 0.175), elevated base excess (P =.02, R = 0.149), low platelet counts (P =.046, R = 0.134), and male gender (P =.028). Stepwise regression analysis revealed that low arterial cord blood pH and male gender were the only independent variables predicting elevated NRBC counts at birth. CONCLUSION: The findings of this study suggest that elevated NRBC counts are associated with specific pregnancy complications rather than uncomplicated prolonged pregnancies in general.