Fetal heart rate and umbilical artery velocity variability in pregnancies complicated by insulin-dependent diabetes mellitus.

OBJECTIVES: To examine the variability in fetal heart rate and absolute flow velocity, which are possible hemodynamic markers of cardiovascular homeostasis in pregnancies complicated by diabetes mellitus. METHODS: Doppler studies of umbilical artery velocity waveforms were performed at 12-21 weeks of gestation in 16 women with well-controlled type I (insulin-dependent) diabetes mellitus. From umbilical artery velocity waveforms of at least 13 s in duration, we determined absolute values and beat-to-beat variability for fetal heart rate and umbilical artery flow velocities and compared these findings with normal controls matched for gestational age. RESULTS: Fetuses of diabetic women displayed increased fetal heart rate variability and umbilical artery peak systolic velocity. Fetal heart rate, umbilical artery time-averaged velocity and variability in umbilical artery flow velocity were not essentially different between the two groups. CONCLUSION: Fetal heart rate variability and umbilical artery peak systolic velocity may be markers for fetal cardiovascular homeostasis in pregnancies complicated by insulin-dependent diabetes mellitus.     

Do heart rate and velocity variability derived from umbilical artery velocity waveforms change prior to clinical pregnancy-induced hypertension?

OBJECTIVE: To investigate the hypothesis that alterations in heart rate variability, peak systolic velocity variability and time-averaged velocity variability in the human umbilical artery may predict early signs of dysfunctional fetal-placental coupling in pregnancies that later develop pregnancy-induced hypertension. METHODS: Doppler flow velocity recordings from the umbilical artery were performed at 10-20 weeks of gestation in 12 nulliparous women who subsequently developed pregnancy-induced hypertension. From umbilical artery velocity waveforms of at least 12 s in duration we determined absolute values and beat-to-beat variability in fetal heart rate, peak systolic and time-averaged velocity and compared these findings with those in normal nulliparous pregnant women matched for gestational age. RESULTS: Absolute values for fetal heart rate, peak systolic and time-averaged velocity as well as beat-to-beat variability in fetal heart rate did not differ significantly between women later developing pregnancy-induced hypertension and normal controls. However, variability in peak systolic velocity and time-averaged velocity were decreased in women who subsequently developed pregnancy-induced hypertension. CONCLUSIONS: Whereas fetal heart rate variability was similar, umbilical artery flow velocity variability was reduced in women developing pregnancy-induced hypertension compared with controls. It is proposed from this study that variability of the umbilical artery flow velocity is associated with mechanical changes in the vascular bed of women who later develop pregnancy-induced hypertension.     

Fetal heart rate and umbilical artery velocity variability in fetuses with congenital cardiac defects: a preliminary study.

OBJECTIVE: To examine whether variabilities in fetal heart rate and umbilical artery flow velocity are possible markers for hemodynamic dysfunction in fetuses with a congenital heart defect. METHODS: Doppler studies of the umbilical artery velocity waveform were performed at 20-35 weeks of gestation in 13 patients with a congenital heart defect. We determined absolute and variability values for heart rate and flow velocities from umbilical artery velocity waveforms of at least 18 s duration. We compared these findings with normal controls matched for gestational age. RESULTS: Fetuses with a congenital heart defect displayed decreased umbilical artery peak systolic and time-averaged velocities. However, variability in peak systolic and time-averaged velocities and fetal heart rate variability were increased compared with normal controls. Absolute fetal heart rates were similar between the two groups. CONCLUSIONS: Marked cardiovascular changes occur in the fetus with a congenital heart defect compared with the normal healthy fetus. We propose that variability in fetal heart rate and umbilical artery blood flow velocity could be additional markers for impaired homeostasis in the presence of fetal congenital heart disease.     

Fetal heart rate and blood flow velocity variability in the presence of increased nuchal translucency: a preliminary study.

OBJECTIVE: To study the power spectrum distribution of heart rate and umbilical artery flow velocity variability in fetuses with increased nuchal translucency thickness (NT). METHODS: Doppler velocity waveforms were collected from long-lasting (>20 s) umbilical artery recordings in 18 fetuses with increased NT (>3 mm) and 18 normal controls matched for gestational age at 11-14 (median, 12) weeks. The NT group included 11 abnormal karyotypes: trisomy 18 (n = 3), 45,X (n = 4), trisomy 21 (n = 3) and a balanced translocation. Absolute heart rate as well as the coefficient of variation for both beat-to-beat heart rate variability and umbilical artery blood flow velocity variability were determined. The ratios of the integrated low-frequency components (0.05-0.2 Hz) and the integrated high-frequency ones (0.25-1.6 Hz; LH ratio) from normalized power spectrum distributions were established to reflect sympathovagal balance. RESULTS: The mean heart rate was not significantly different between the two groups. However, mean heart rate variability and time-averaged flow velocity variability were significantly increased in the NT group, while there was no significant difference in the LH ratios between the two groups. The mean umbilical artery pulsatility index was significantly higher in the NT group. CONCLUSION: The autonomic nervous system does not seem to play a role in the altered cardiovascular homeostasis in the presence of increased fetal NT.     

Doppler assessment of the normal early fetal circulation.

Combined transvaginal and transabdominal Doppler ultrasound allows recording of fetal intra- and extracardiac flow velocity waveforms in late first- and early second- trimester pregnancies. At 10-12 weeks, end-diastolic flow velocities were always absent in the fetal descending aorta and umbilical artery, but were present in over half of the intracerebral artery waveforms. The pulsatility index in the three vessels decreased significantly with advancing gestational age, suggesting a reduction in fetal and umbilical placental vascular resistance. Peak velocities during atrial contraction (A-wave) were nearly twice as high as those during early diastolic filling (E-wave), reflecting low ventricular compliance. Continuous forward flow in the umbilical vein was associated with a pulsatile systolic and diastolic forward flow in the ductus venosus. Retrograde flow was only present in the inferior vena cava.     

Fetal and uteroplacental blood flow in prolonged pregnancies. A clinical study.

In a prospective study during 1 year, 102 women with prolonged pregnancies (more than 294 completed gestational days) were followed with serial pulsed Doppler blood flow examinations every 2nd day, either to spontaneous onset of labor (n = 82) or to induction of labor due to subsequently occurring complications (n = 20). Mean aortic blood velocity did not change significantly with gestational age beyond 294 days either in fetuses with normal outcome or in fetuses that developed asphyxia at birth. The flow velocity waveforms in the descending aorta, the umbilical artery, the common carotid artery and the uterine artery did not change significantly compared to the values at term. Abnormal flow velocity waveforms in the fetal descending aorta, umbilical artery or uterine artery had no significant relationship to fetal asphyxia. Absence of diastolic flow velocities was not found in any of the vessels examined, indicating that the fetuses did not suffer from chronic hypoxia in utero and that aging of the placenta did not alter fetal and uteroplacental blood flow. Notching of the aortic flow velocity waveform was a common finding among prolonged pregnancies. The hemodynamic implications and consequences of this phenomenon are discussed.     

Changes in fetal hemodynamics with ritodrine tocolysis.

OBJECTIVE: To evaluate the effect of ritodrine on the fetal cardiovascular system. METHODS: Cardiac and extracardiac Doppler waveforms were recorded in 12 fetuses prior to and during ritodrine therapy used for preterm labor. Maternal and fetal heart rates, the Doppler pulsatility indices of the umbilical artery, middle cerebral artery, descending thoracic aorta and renal artery, and time velocity integrals of the atrioventricular valves and the ductus arteriosus, were measured. RESULTS: Ritodrine infusion caused an increase in maternal and fetal heart rates, the left cardiac output as measured by the product of time velocity integral and heart rate, and the pulsatility index of the middle cerebral artery, and a decrease in the pulsatility index of the umbilical artery. CONCLUSIONS: Ritodrine infusion may alter placental and cerebral blood flow and may have a selective effect on the left side of the heart.     

Fetal heart rate and umbilical artery flow velocity variability in intrauterine growth restriction: a matched controlled study.

OBJECTIVES: To study heart rate and umbilical artery blood flow velocity variability in growth-restricted fetuses and investigate the influence of the autonomic nervous system on these parameters. METHODS: Doppler velocity waveforms were collected from long-lasting umbilical artery recordings in 15 fetuses with growth restriction and 15 normal age-matched controls at 23-35 weeks of gestation. Absolute heart rate and umbilical artery blood flow velocity as well as the coefficient of variation were determined. Using power spectral analysis the low- and high-frequency bands of heart rate variability and blood flow velocity variability were calculated. The low-to-high (LH) ratio of heart rate variability and blood flow velocity variability were examined as a measure of sympathovagal balance. RESULTS: In growth-restricted fetuses umbilical artery velocities were significantly reduced. Heart rate variability was significantly reduced in the presence of growth restriction, but no significant difference was demonstrated for blood flow velocity variability. The LH ratio for heart rate variability was significantly decreased in growth restriction, but no difference in LH ratio was demonstrated for blood flow velocity variability. CONCLUSION: Flow velocity variability in growth restriction seems not to be predominantly influenced by the autonomic nervous system, whereas the decreased heart rate variability seems to be influenced by altered sympathetic-parasympathetic balance.     

Longitudinal changes in the ductus venosus, cerebral transverse sinus and cardiotocogram in fetal growth restriction.

OBJECTIVE: To evaluate the changes in flow velocity waveforms in the transverse cerebral sinus in growth-restricted fetuses and to correlate these changes with (1) flow velocity waveforms in the ductus venosus and (2) changes in computerized analysis of the fetal cardiotocogram. DESIGN: Fetuses between 22 and 37 weeks' gestation with an estimated fetal weight below the fifth centile were included in this prospective longitudinal study. Doppler measurements of the umbilical artery, descending aorta, middle cerebral artery, transverse cerebral sinus and ductus venosus were recorded. Fetal heart rate was analyzed by a computer system according to the Dawes-Redman criteria. RESULTS: We measured a significant correlation between pulsatility index in the cerebral transverse sinus and in the ductus venosus over the study period and at delivery. There was a negative correlation between these indices and short- and long-term variability of the fetal heart rate. There was a parallel increase in pulsatility in the ductus venosus and the transverse cerebral sinus. These changes were inversely correlated with fetal heart rate variability and preceded fetal distress. CONCLUSION: Cerebral venous blood flow in IUGR fetuses may be a useful additional investigation to discriminate between fetal adaptation and fetal decompensation in chronic hypoxemia.     

Effects of maternal hyperoxygenation on ductus venosus flow velocity waveforms in normal third-trimester fetuses.

On the basis of the data obtained in sheep fetuses showing a high interdependence between umbilical vein oxygenation and ductus venosus flow, we investigated the effect of maternal hyperoxygenation on ductus venosus velocity waveforms in normal third-trimester human fetuses. Ductus venosus velocity waveforms were recorded by using color and pulsed Doppler ultrasonography before and after 15 min of maternal administration of humidified 60% oxygen. During maternal hyperoxygenation, there was a significant increase of both estimated peak velocities during systole, diastole and atrial contraction and the mean temporal velocity during the total cardiac cycle and systolic and diastolic portions. On the other hand, during maternal hyperoxygenation, no significant changes were found in fetal heart rate or in the ratios between peak velocities and mean temporal velocities during systole and diastole. These findings suggest a close relationship between fetal oxygenation and ductus venosus velocity waveforms that may be useful in monitoring fetal hypoxemia.     

Power spectrum analysis of heart rate and blood flow velocity variability measured in the umbilical and uterine arteries in early pregnancy: a comparative study.

OBJECTIVE: To compare power spectral derived variability parameters from the fetal side of the placental circulation with those from the maternal side of the placental circulation, during early pregnancy. METHODS: Doppler velocity waveforms were obtained from both the umbilical and the uterine arteries in a study group of 40 pregnant women between 10 and 14 (n = 25) and 15 and 20 (n = 15) weeks of gestation. The coefficient of variation of both the beat-to-beat heart rate variability and the blood flow velocity variability was determined. The ratio of the integrated low-frequency components (< 0.2 Hz) and the integrated high-frequency components (> 0.2 Hz) from normalized power spectrum analysis (LH-ratio) was established, to reflect sympathovagal balance. RESULTS: The coefficient of variation and LH-ratio of fetal heart rate variability constitute only a fraction of the same maternal heart rate variability parameters. Nevertheless a highly significant increase (P < 0.001) in LH-ratio was demonstrated with advancing gestational age. The coefficient of variation and LH-ratio of blood flow velocity variability were significantly lower in the fetal umbilical artery only in the 10-14-weeks' gestation group. Due to a decrease of the maternal uterine blood flow velocity variability parameters with advancing gestational age, statistically equal fetal and maternal values for coefficient of variation and LH-ratio were found in the 15-20 weeks' gestation group. CONCLUSIONS: The increase in LH-ratio of fetal heart rate variability indicates functional development of the fetal autonomic nervous system at 15-20 weeks' gestation. The umbilical blood flow velocity variability may be secondary to maternal uterine arterial flow variability rather than due to primary changes in fetal cardiovascular function.     

Indomethacin and amniocentesis-induced changes in fetal flow velocity waveforms.

The effect of genetic amniocentesis on flow velocity waveforms in the fetal aorta and the umbilical artery, and fetal heart rate and their correlation with uterine contractions was examined in 75 pregnant women who underwent this procedure. Forty-three were untreated and 32 were pretreated with indomethacin. Median maternal age was 36 years and median gestational age was 18 weeks. The resistance index of waveforms from the fetal aorta was stable at 0.8 throughout the approximately 20-h study period in both groups, but the systolic/diastolic ratio in the umbilical artery increased significantly after amniocentesis in the untreated group, and remained stable in the treated group. Fetal heart rate remained at about 150 beats/min throughout all measurements in both groups. These findings indicate that genetic amniocentesis causes an increase in downstream resistance in the umbilical artery which, however, remains within normal limits. This mild fetoplacental response to amniocentesis can be suppressed by the administration of a potent prostaglandin inhibitor like indomethacin.     

Blood flow velocity waveforms of the fetal pulmonary artery and the ductus arteriosus: reference ranges from 13 weeks to term.

OBJECTIVE: To establish reference ranges for blood flow velocity waveforms of the fetal main pulmonary artery and the ductus arteriosus during the second and third trimesters of pregnancy. METHODS: A prospective cross-sectional echocardiographic study was performed in 222 normal fetuses from 13 to 41 weeks of gestation using high resolution/color Doppler ultrasound equipment. RESULTS: Gestational age-specific reference ranges are given for peak velocity across the pulmonary valve, velocities in the ductus arteriosus, peak systolic velocity in the ductus arteriosus-to-peak velocity across the pulmonary valve ratio, ductal systolic velocity-to-diastolic velocity ratio, ductal resistance index and ductal pulsatility index. In the ductus arteriosus, increasing fetal heart rate was significantly associated with increasing end-diastolic velocity and decreasing systolic-to-diastolic ratio, decreasing resistance index, and decreasing pulsatility index. CONCLUSIONS: Based on a prospective study in more than 200 normal fetuses, the data provide gestational age specific reference ranges for blood flow velocity waveforms of the fetal pulmonary artery and the ductus arteriosus. The reference ranges may be helpful in prenatal diagnosis of cardiac malformations and ductal obstruction from 13 to 41 weeks of gestation.     

Normal cardiac flow velocities at 14-16 weeks of gestation measured by transvaginal ultrasound.

OBJECTIVE: Doppler ultrasound has been used to study the flow velocities through the valves and arteries of the fetal heart. Using transvaginal sonography, we sought to determine normal values for flow velocities through the fetal heart valves at 14-16 weeks of gestation. METHODS: Eighty-seven normal fetuses were examined. The flow velocity waveforms were visualized using Doppler ultrasound with the sample volume calipers placed just distally to the four fetal valves. Peak E- and A-wave velocities were recorded for the tricuspid and mitral valves and peak systolic flow velocities were recorded for the ascending aorta and pulmonary arteries. Linear regression for comparison of flow velocities with gestational age was performed. RESULTS: There was no significant correlation between any of the velocities and gestational age. CONCLUSIONS: Flow velocities through the fetal cardiac valves remain unchanged at 14-16 weeks of gestation as measured by transvaginal Doppler sonography.     

Fetal Doppler velocimetry at high altitude.

OBJECTIVES: To determine impedance and velocity characteristics of the fetal circulation using Doppler ultrasound, at extremely high altitude (4300 m) in the Peruvian Andes compared to an ethnically similar population at sea level. METHODS: This was a cross-sectional study of 196 women resident at high altitude (Cerro de Pasco, 4300 m above sea level) and 196 women resident at sea level (Lima) with normal singleton pregnancies. Pulsatility index (PI), maximum velocity (Vmax) and minimum velocity (Vmin) in the umbilical artery, the descending aorta, the middle cerebral artery and the ductus venosus were compared between the two populations using fractional polynomial regression analysis. RESULTS: The PI was higher at high altitude than at sea level in the umbilical artery (regression coefficient = 0.112, P < 0.001), and not significantly different in the descending aorta, middle cerebral artery and ductus venosus. Vmax was lower at high altitude than at sea level in all three arterial vessels assessed; Vmin was lower in two: the umbilical artery and the descending aorta. The high-altitude/sea-level ratios for umbilical artery Vmax and Vmin were 0.93 and 0.82, respectively (P < 0.001 for each), the ratios for descending aorta Vmax and Vmin were 0.93 and 0.89, respectively (P = 0.003 and P < 0.001, respectively), and the regression coefficient for the middle cerebral artery Vmax was -2.844 (P = 0.003). There was no significant difference in the middle cerebral artery Vmin or in the ductus venosus Vmax and Vmin. CONCLUSIONS: Despite the lower ambient oxygen at high altitude and an increase in umbilical artery PI, the fetal circulation does not exhibit a 'brain sparing effect'. This and the overall decrease in blood flow velocities in the fetal circulation at high altitude may be due to the increased fetal hematocrit, which will result in increased blood viscosity.     

Changes in fetoplacental vessel flow velocity waveforms following maternal administration of betamethasone.

OBJECTIVE: To determine the timing of the onset of the umbilical artery flow velocity waveform changes following maternal administration of betamethasone in pregnancies complicated by umbilical artery absent end-diastolic flow, and to explore whether these changes are associated with flow velocity waveform changes in other fetoplacental vessels. SUBJECTS AND METHODS: This was a prospective study of 12 women with pregnancies complicated by umbilical artery absent end-diastolic flow. Flow velocity waveforms were recorded from the umbilical artery, fetal middle cerebral artery, renal artery, aorta and ductus venosus, before and after maternal betamethasone administration, using real-time pulsed wave Doppler. RESULTS: In all 12 pregnancies, the administration of maternal betamethasone was followed by the return of end-diastolic flow within 24 h. End-diastolic flow was first observed at 4 h and was present in all women studied at 8 h. In addition, there was a statistically significant decrease in the pulsatility index in the fetal aorta at 8 h and the middle cerebral artery at 24 h. No change was observed in the ductus venosus or the renal artery flow velocity waveforms. CONCLUSION: The findings suggest that, in pregnancies complicated by absent end-diastolic flow in the umbilical artery, maternally administered betamethasone induces a return in umbilical artery end-diastolic flow as early as 4 h, along with widespread vasodilatation throughout the fetoplacental vasculature.     

Nifedipine therapy for preterm labor: effects on placental, fetal cerebral and atrioventricular Doppler parameters in the first 48 hours.

OBJECTIVE: To assess the effect of nifedipine tocolysis on Doppler parameters of the uterine, umbilical and fetal middle cerebral arteries and atrioventricular valves in the first 48 h of therapy. METHODS: Doppler waveforms of uterine, umbilical and middle cerebral arteries and both atrioventricular valves were measured from 28 pregnant women and fetuses prior to and during nifedipine therapy for preterm labor. Maternal and fetal heart rates (FHR), maternal systolic and diastolic blood pressure, and the Doppler pulsatility index (PI) of the uterine, umbilical and middle cerebral arteries were measured. The cerebroplacental ratio (middle cerebral artery PI/umbilical artery PI) was calculated. The total time velocity integrals (TVIs) of tricuspid and mitral valves and their E- and A-wave peak velocity ratio (E/A) were measured. Friedman repeated-measures analysis of variance was used to compare the variables before and after nifedipine therapy. If significant differences were found, Wilcoxon's signed ranks test was used to analyze the difference between the two variables. A P-value of < 0.05 was considered significant. RESULTS: Nifedipine maintenance was associated with a significant decline in maternal systolic and diastolic blood pressure after 24 h, while maternal heart rate and FHR were unaffected. The uterine artery PI had decreased significantly at 24 and 48 h, while the umbilical artery PI did not change significantly. The middle cerebral artery PI had decreased significantly at 24 and again at 48 h. A significant fall in the cerebroplacental Doppler ratio was maintained beyond 24 h. The mean E/A values, TVIs and TVI x FHR values at 24 and 48 h were unchanged from the baseline values. CONCLUSIONS: Nifedipine maintenance tocolysis is associated with a significant decline in uterine artery and middle cerebral artery Doppler indices 24 h after the first dose. Fetal cardiac diastolic function is unaffected and the significant redistribution observed after 24 h is likely to be attributable to altered cerebral blood flow.     

Doppler blood flow velocity waveforms in the fetal renal arteries: variability at proximal and distal sites in the right and left arteries.

OBJECTIVE: To investigate variability in pulsatility/resistance indices and absolute velocities of blood flow in fetal renal arteries dependent on side and sampling site within each vessel. METHODS: Doppler blood flow measurements of pulsatility index (PI), resistance index (RI) and peak systolic velocity (PSV) and end-diastolic velocity (EDV) were performed in the renal arteries of 27 fetuses between 236 and 247 days of gestation. Velocity waveforms were sampled in both the right and left renal arteries at two different sites: proximally, close to the aorta, and distally, before any major visible bifurcation of the vessels. The intraobserver variation was measured in 15 additional fetuses. RESULTS: Mean values of PI and RI were similar in the right and left renal arteries and at the proximal and distal sampling sites of these arteries. Mean PSV and EDV were higher at the proximal compared to the distal site on both sides. For all parameters the 95% limits of agreement between measurements made in the right and left arteries and at proximal and distal sites were wide but tended to be narrower for the left renal artery and at the distal site. Intraclass correlation coefficients for intraobserver variability were 0.88, 0.89, 0.83 and 0.81 for PI, RI, PSV and EDV, respectively. CONCLUSIONS: It is important to standardize the precise site at which Doppler blood flow velocity waveform measurements are made in the renal arteries of the fetus. On the basis of our observations, we suggest that the left renal artery is the preferred vessel for sampling and that measurements should be made in the renal arterial trunk away from the aorta and before any visible branches.     

Assessment of variability of renal blood flow Doppler parameters during the menstrual cycle in women.

OBJECTIVE: To estimate variability of renal flow Doppler parameters during the menstrual cycle in young women, and to explore whether the parameters oscillate substantially throughout the cycle. METHODS: The peak systolic, mean, and end-diastolic velocities, pulsatility (PI) and resistance (RI) indices, acceleration time (AT) and index (AI) of the right renal artery were measured nine times during the cycle with duplex sonography in 14 healthy women (age range, 23-25 years), and correlated with plasma concentrations of 17beta-estradiol and progesterone. Coefficient of variation (CV), interclass correlation (rho), and repeatability coefficients (RC) were used to measure the variability. RESULTS: The measures of the variability for AI and AT were: CV = 45.4% and 37.3%; rho = 0.25 and 0.15; RC = 10.1 and 99.5, respectively. The CV for flow velocities varied from 24.1% to 25.5%, rho from 0.49 to 0.50, RC from 22.7 for end-diastolic to 63.3 for peak systolic velocity. The respective figures for PI and RI were: CV = 17% and 8.3%; rho = 0.21 and 0.29; RC = 0.53 and 0.15. Fluctuations of the flow parameters, hematocrit, hemoglobin, heart rate, and systolic blood pressure during the menstrual cycle were insignificant, while the diastolic blood pressure decreased by about 7 mmHg (P < 0.01) in the luteal phase. CONCLUSION: The variability of renal flow Doppler parameters during the menstrual cycle in young healthy women is substantial. However, fluctuations of the values of the parameters throughout the cycle were non-significant.     

彩色多普勒观察高危妊娠时硝酸甘油对胎儿－胎盘血流动力学的影响

本文介绍应用彩色多普勒超声技术观察３０例高危妊娠孕妇口含硝酸甘油前后的脐动脉、胎儿大脑中动脉、胎儿腹主动脉的血流动力学改变。结果：用药后脐动脉的搏动指数（ＰＩ）、阻力指数（ＲＩ）和Ｓ／Ｄ值均有显著改变（Ｐ＜０．００１），胎儿大脑中动脉和胎儿腹主动脉的ＰＩ、ＲＩ和Ｓ／Ｄ值无显著变化。而孕妇血压、心率和胎心率未见明显改变，呈现良好的耐受性。表明应用硝酸甘油可明显降低脐－胎盘血管阻力，是改善胎儿血氧供应的简便、有效的方法。而彩色多普勒超声显像则为围产期好高征早期诊断及疗效观察提供了重要的依据。