正常胎儿肺静脉血流多普勒频谱分析及其临床意义

目的研究正常胎儿肺静脉血流频谱及其血流参数的正常参考范围。方法应用彩色多普勒超声诊断系统检测233例20～40孕周的正常胎儿的肺静脉血流频谱，测量其血流参数：心室收缩期峰值速度(S)、心室舒张期峰值速度(D)、心房收缩期速度(A)、时间速度积分(TVI)，计算S／D、静脉峰值速度指数(PVI)、静脉搏动指数(PI)。结果正常胎儿典型肺静脉血流频谱为三相波型：心室收缩期波峰、心室舒张期波峰及心房收缩期波谷，前向血流持续整个心动周期。S、D、A及TVI与胎龄呈良好的正相关，PVI、PI与胎龄呈良好的负相关，S／D与胎龄无明显相关关系。结论胎儿肺静脉血流频谱的产生主要由于左房与肺静脉之间的压差引起，左心房压力的改变有可能影响肺静脉血流频谱。胎儿肺静脉血流频谱及血流参数S、D、TVI、PVI、PI与孕周有良好的相关性。     

静脉导管的多普勒血流频谱在孕早期胎儿先天性心脏畸形筛查中的研究

目的 探讨静脉导管的多普勒血流频谱在孕早期胎儿先天性心脏畸形筛查中的临床应用价值。方法 应用彩色多普勒超声诊断系统检测800例孕11～14周随诊的单胎孕妇胎儿的静脉导管血流频谱。对静脉导管血流频谱异常的胎儿分别于孕18～20周和孕22～24周进行详细的超声心动图检查，其余孕妇则于孕18～24周行一次详细的超声心动图检查。结果 1．正常胎儿静脉导管的血流频谱为心室收缩期波峰(S)、心室舒张期波峰。(D)和心房收缩期波谷(A)在整个心动周期中均为前向血流；2．22例先天性心脏畸形胎儿中18例静脉导管的A波出现反转，2例出现A波消失，2例无明显变化；3．静脉导管血流频谱异常在孕早期(11～14周)筛查胎儿先天性心脏畸形的敏感性为91％，特异性为93．2％，阳性预测值为13．1％，阴性预测值为100％，准确性为83％。结论 静脉导管血流频谱异常可作为孕早期(11～14周)胎儿先天性心脏畸形的一个筛查指标。     

11～14孕周正常胎儿静脉导管血流参考范围

目的建立孕早期正常胎儿静脉导管（DV）不同时相血流速和各参数参考范围。方法应用彩色多普勒超声测定800例11~14孕周正常单胎胎儿DV血流参数：心室收缩期峰值流速（S-peak）,心室舒张期峰值流速（D-peak）,心房收缩期最大流速（A-wave）,搏动指数（PI）,阻力指数（R I）和S-peak/A-wave（S/A）。结果 7例出现生理性零及20例反向房收缩（RA）波;S-peak（30.26~36.46 cm/s）,D-peak（24.71~30.62 cm/s）,A-wave（11.13~14.33 cm/s）,与孕龄正相关均有显著性差异（P〈0.01）;PI（0.84~1.66）,R I（0.64~0.67）,S/A（2.71~3.11）,与孕龄相关性差（P〉0.05）。结论 11~14孕周正常胎儿DV频谱中存在着3.3%的生理性零或RA波,流速随着孕龄增加而增加;而R I、PI、S/A变化不明显。     

正常胎儿静脉血流频谱分析及其临床意义

目的对正常胎儿不同孕周肺静脉、下腔静脉、静脉导管血流频谱进行分析,探讨正常胎儿静脉循环血流动力学变化。方法采用高分辨率血流显像(HDF)技术显示200例20～40周正常胎儿肺静脉、静脉导管及下腔静脉,测量其血流参数:心室收缩期峰值速度(S),心室舒张期峰值速度(D),心房收缩期速度(A)。结果正常胎儿肺静脉、下腔静脉及静脉导管均呈三相波:心室收缩期波峰,心室舒张期波峰及心房收缩期波谷,其中肺静脉及静脉导管频谱前向血流持续整个心动周期,下腔静脉心房收缩期波谷与心室收缩期波峰及心室舒张期波峰呈反向;肺静脉S、D及A随着孕龄的增大而增加(P<0.05);下腔静脉S、D及A在妊娠中早期流速较低,在28周之后流速明显增高(P<0.05);静脉导管S、D及A在孕32+1～36周流速最高(P<0.05);36周后与32+1～36周比较无统计学差异。结论胎儿肺静脉、下腔静脉及静脉导管的流速随着孕周的增加有不同的变化。     

静脉导管的多普勒血流流速曲线在筛选胎儿先天性心脏病中的临床意义

目的：探讨静脉导管的血流流速曲线在筛选和协助早期诊断胎儿先天性心脏病中的临床意义。方法：应用彩色多普勒超声诊断系统检测240例14－41孕周的正常胎儿和20例先天性心脏病胎儿的静脉导管血流流速曲线，并计算静脉导管血流阻力指数、搏动指数及心室收缩期峰值速度与心房收缩期最大流速比值。结果：①正常胎儿静脉导管的血流流速曲线呈特殊的波形：心室收缩期波峰S、心室舒张期波峰D和心房缩期波谷A，前向血流持续整个心动周期；②20例先天性心脏病胎儿中8例静脉导管的A波出现反转，9例A波降低或缺失，3例无明显变化。先天性心脏病胎儿组静脉导管血流指数较胎龄相匹配的正常胎儿组增高，两组比较差异有显著性意义（P＜0．05）。结论：彩色多普勒超声检测胎儿静脉导管的血流流速曲线可筛选或协助早期诊断胎儿先天性心脏病。     

正常中晚孕期胎儿肺静脉血流频谱分析

目的 探讨正常中晚孕期单胎胎儿肺静脉血流频谱特点,建立肺静脉血流参数正常参考值范围.方法 应用彩色多普勒超声检测340例19～40孕周正常单胎胎儿肺静脉血流参数:心室收缩期峰值速度(S)、心室舒张期峰值速度(D)、心房收缩期血流速度(A)、速度时间积分(velocity time integral,VTI)、静脉峰值速度指数(peak velocity index,PVI)、静脉搏动指数(pulsatility index,PI)、心室收缩期峰值速度与心室舒张期峰值速度比值(S/D).结果 肺静脉血流参数S、D、A、VTI随孕龄增大逐渐增高,PVI、PI随孕龄增大逐渐降低,各参数拟合的回归方程均有统计学意义;S/D与孕龄无线性关系.所有病例心房收缩期均无反向血流出现.结论 正常胎儿肺静脉血流频谱形态与成人不同.相关参数正常参考值范围曲线可为评价病理情况下胎儿肺静脉血流变化及心功能改变提供依据.     

彩色多普勒超声观察不同孕周正常胎儿动脉血流的价值

目的：探讨不同孕周胎儿肾动脉（RA）、脐动脉（UA）、大脑中动脉（MCA）血流参数的变化情况,确定正常胎儿RA、UA、MCA血流参考值,并分析RA、UA、MCA血流参数与孕龄的关系。方法选取2013年1～12月在该院行产前检查的185例孕周为4～41周的正常单胎孕妇为研究对象,采用彩色多普勒超声测量胎儿 RA、UA、MCA的阻力指数（RI）、搏动指数（PI）、收缩期峰值流速（PS）及收缩期峰值流速与舒张末期流速比值（S/D）。结果随着孕周的增加,胎儿RA、UA、MCA中PS值显著增加,而RA、UA中RI、PI、S/D值显著减少。经相关性分析可知,RA、UA、MCA中RI、PI、S/D与孕周呈负相关性（P＜0．05）,而RA、UA、MCA中PS与孕周呈正相关性（P＜0．05）。结论应用彩色多普勒测量不同孕周胎儿RA、UA、MCA血流动力学参数能有效了解胎儿颅脑循环、胎盘循环及全身血流循环状态。通过建立正常胎儿血流参数参考范围可为超声预测胎儿宫内生长情况提供参考依据。     

孕11～40周正常胎儿静脉导管血流频谱分析

目的分析不同孕周正常胎儿静脉导管的频谱特征及血流频谱参数,得到不同孕周胎儿各频谱参数的正常参考值范围。方法 2011年6月-9月检测记录不同孕周胎儿的静脉导管波形及各频谱参数,统计各频谱参数的正常参考值范围,并评估与其孕周的相关性。结果胎儿静脉导管的频谱速度参数与孕周呈正相关,阻力参数与孕周呈负相关,均以11～20周变化趋势较明显,其中3.59%的胎儿静脉导管频谱出现异常。结论正常胎儿的静脉导管血流参数与孕周有较好的相关性,静脉导管频谱在孕16周前可出现生理性的异常。     

中晚孕期正常胎儿静脉导管血流动力学研究

目的 建立中晚孕期正常胎儿静脉导管多普勒血流参数参考范围。方法 应用彩色多普勒超声检查138例16-41孕周正常单胎胎儿。在静脉导管入口处记录静脉导管血流波形，测定血流参数包括：心室收缩期峰值流速（S）、心室舒张期峰值流速（D）、心房收缩期最大流速（A）、平均流速（Vmean）、S／A值、S／D值、（S-A）／S值、（S-A）／D值和（S-A）／Vmean值。结果 正常胎儿静脉导管的血流参数S、D、A、Vmean随着孕龄的增加而增加（均P〈0．01或P〈0．05）；而S／A、（S-A）／S、（S-A）／Vmean和（S-A）／D值随着孕龄增加而减低（均P〈0．01或P〈0．05），S／D与孕龄相关性差（r=0．1，P〉0．05）。结论 正常胎儿静脉导管血流波形呈特殊的三相波形，血流速度随着孕龄增加而增加，而阻力指数随着孕龄增加而减低，S／D值在妊娠中持续不变。     

超声观察中晚孕期正常胎儿脐动脉和脑、肾动脉血流动力学

目的 探索正常胎儿脐动脉(UA)、大脑中动脉(MCA)和肾动脉(RA)血流参数随孕期变化的规律;建立正常胎儿不同孕期UA、MCA和RA血流参数的参考值范围。方法 应用彩色多普勒血流显像(CDFI)检测220胎21~41孕周正常单胎胎儿UA、MCA和RA血流,测量收缩期峰值流速(PS)、搏动指数(PI)、阻力指数(RI)及收缩期峰值流速与舒张末期流速比值(S/D)。结果 正常胎儿UA、MCA和RA的PS值随着孕周增加而增加;UA和RA的PI、RI和S/D值随着孕周增加而减低;而MCA的PI、RI和S/D值随着孕周增加呈先升高后降低的抛物线状。至足月,PS参考值范围分别为:UA PS(54.96±14.57)cm/s、MCA PS(65.11±11.35)cm/s和RA PS(58.54±10.72)cm/s;UAS/D测值为2.14±0.30;RA RI测值为0.79±0.04;MCA RI测值为0.72±0.05。所有参数的变化在不同孕周组差异均有统计学意义(P均<0.05)。结论 CDFI产前检测胎儿UA、MCA和RA随着孕期变化的血流动力学参数可以同时了解胎儿胎盘循环、颅脑循环及周围循环状态。不同孕期的血流参数的参考值范围可为超声预测胎儿宫内缺氧提供理论依据。     

Reference values for ductus venosus Doppler flow measurements at 10-14 weeks of gestation.

OBJECTIVES: To calculate reference ranges for ductus venosus Doppler measurements obtained transabdominally at 10-14 weeks of gestation. DESIGN: Two hundred and one normal fetuses with a crown-rump length (CRL) ranging from 38 to 88 mm were examined in a cross-sectional study. The pulsatility index for veins (PIV), peak velocity during ventricular systole (S-wave), lowest forward velocity during atrial contraction (A-wave) and time-averaged maximum velocity (TAMXV) were recorded from the ductus venosus. Flow velocity waveforms were also classified as normal or abnormal according to the presence (normal) or absence or reversal (abnormal) of frequencies during atrial contraction. RESULTS: Three of 201 fetuses showed an abnormal flow pattern (1.5%; 95% exact confidence interval, 0.3-4.3%). In the 198 fetuses with a normal flow pattern, the mean PIV ranged from 1.07 at a CRL of 38 mm to 1.00 at a CRL of 88 mm (r = -0.093; P = 0.19). A significant increase in mean blood flow velocity with increasing CRL was noted for the S-wave (27.0 cm/s to 33.6 cm/s; r = 0.17; P = 0.02), the A-wave (5.9 cm/s to 7.8 cm/s; r = 0.14; P = 0.04) and the TAMXV (19.4 cm/s to 25.3 cm/s; r = 0.19; P < 0.01). Crown-rump length-specific reference ranges for each parameter were calculated using the method of scaled absolute residuals. CONCLUSIONS: Abnormal ductus venosus flow patterns could be observed in normal fetuses, even if they ocurred with a low prevalence. Reference values for Doppler measurements were established in fetuses with normal patterns of flow.     

The role of fetal nuchal translucency and ductus venosus Doppler at 11-14 weeks of gestation in the detection of major congenital heart defects.

OBJECTIVE: To determine whether, in a selected high-risk population, Doppler velocimetry of the ductus venosus can improve the predictive capacity of increased nuchal translucency in the detection of major congenital heart defects in chromosomally normal fetuses at 11-14 weeks of gestation. METHODS: Ductus venosus Doppler ultrasound blood velocity waveforms were obtained prospectively at 11-14 weeks of gestation in 1040 consecutive singleton pregnancies. Waveforms were classified either as normal in the presence of a positive A-wave, or as abnormal if the A-wave was absent or negative. All cases were screened for chromosomal defects by a combination of maternal age and fetal nuchal translucency thickness. In 484 cases karyotyping was performed. Those fetuses found to be chromosomally normal by prenatal cytogenetic analysis, and which had abnormally increased nuchal translucency and/or abnormal ductus venosus Doppler velocimetry, underwent fetal echocardiography at 14-16 weeks of gestation. Ultrasound examination was repeated at 22-24 weeks of gestation in all women. The sensitivity, specificity and positive and negative predictive values for the detection of major cardiac defects of increased nuchal translucency thickness alone, ductus venosus Doppler alone and increased nuchal translucency thickness in association with abnormal ductus venosus Doppler were determined. RESULTS: In 29 of 998 fetuses presumed to be chromosomally normal, reversed or absent flow during atrial contraction was associated with increased (> 95(th) centile for crown-rump length) nuchal translucency. Major cardiac defects were observed in 9 of these 29 fetuses. No other major cardiac abnormalities were found in chromosomally normal fetuses in spite of the presence of either increased nuchal translucency alone or abnormal ductus venosus velocimetry. A total of 25 cardiac malformations were observed in the population. Fifteen were associated with aneuploidy and 10 fetuses had a normal karyotype. Nine of the 10 had major cardiac anomalies and one had a ventricular septal defect. The nine cases with normal karyotype and major cardiac anomalies had both increased nuchal translucency and abnormal ductus venosus flow velocity waveforms. CONCLUSION: In chromosomally normal fetuses with increased nuchal translucency, assessment of ductus venosus blood flow velocimetry could improve the predictive capacity for an underlying major cardiac defect.     

Ductus venosus Doppler study in fetuses with homozygous alpha-thalassemia-1 at 12 to 13 weeks of gestation.

OBJECTIVE: Fetuses affected by homozygous alpha-thalassemia-1 are anemic from the first trimester of pregnancy. We investigated ductus venosus Doppler velocimetry in these affected fetuses at 12-13 weeks of gestation. DESIGN: Prospective observational study. SUBJECTS: Women referred for the prenatal diagnosis of homozygous alpha-thalassemia-1 before 14 weeks of gestation. METHODS: All fetuses underwent pulsed Doppler investigations following color flow mapping at 12 or 13 weeks of gestation. Homozygous alpha-thalassemia-1 was diagnosed by DNA or hemoglobin study. The ductus venosus Doppler indices--Vmax (peak velocity during ventricular systole), Vmin (minimum forward velocity during atrial systole), TAMX (time-averaged maximum velocity), PIV (pulsatility index for veins, Vmax-Vmin/TAMX), PLI (preload index, Vmax-Vmin/Vmax) and Vmax/Vmin ratio--were compared between the affected fetuses and fetuses unaffected by homozygous alpha-thalassemia-1. RESULTS: Between June 1998 and October 1999, 102 eligible women were recruited. Fetal ductus venosus Doppler study was successful in 96 pregnancies (94%). Of these, 20 fetuses were affected by homozygous alpha-thalassemia-1. None of them showed hydropic changes at the time of Doppler study. The affected fetuses had significantly higher ducts venosus Vmax (30% increase), Vmin (50% increase) and TAMX (20% increase) and significantly lower Vmax/Vmin ratio, PIV and PLI values. CONCLUSION: Fetuses affected by homozygous alpha-thalassemia-1 at 12-13 weeks had increased forward flow velocities in the ductus venosus throughout the cardiac cycle. The increase of venous return is consistent with our previous report of cardiac dilatation and an increase of cardiac output in the affected fetuses at this stage as a compensatory mechanism for anemia and hypoxia. However, extensive overlap of the ductus venosus Doppler indices between affected and unaffected fetuses precludes its use in predicting anemia at 12-13 weeks.     

Cardiac defects in chromosomally normal fetuses with abnormal ductus venosus blood flow at 10-14 weeks.

OBJECTIVE: To assess a possible relationship between ductus venosus blood flow abnormalities and cardiac defects in chromosomally normal fetuses with increased nuchal translucency thickness at 10-14 weeks of gestation. METHODS: Ductus venosus Doppler ultrasound blood flow velocity waveforms were obtained at 10-14 weeks' gestation immediately before fetal karyotyping in 200 consecutive singleton pregnancies with increased nuchal translucency. Fetal echocardiography was subsequently carried out in those with normal fetal karyotype. RESULTS: Reverse or absent flow during atrial contraction was observed in 11 of the 142 chromosomally normal fetuses with increased nuchal translucency. Major defects of the heart and/or great arteries were present in seven of the 11 with abnormal ductal flow and increased nuchal translucency, but in none of the 131 with normal flow. CONCLUSION: These preliminary results suggest that abnormal ductus venosus blood flow in chromosomally normal fetuses with increased nuchal translucency identifies those with an underlying major cardiac defect.     

Ductus venosus index: a method for evaluating right ventricular preload in the second-trimester fetus.

This study was designed to examine ventricular preload by measuring the ductus venosus index during the second trimester of pregnancy. A total of 137 women were entered into the study. Each fetus was examined with real-time, color and pulsed Doppler ultrasound. The color Doppler maximal velocity setting was adjusted so that the umbilical vein was homogeneous in color, did not demonstrate aliasing, and filled the venous lumen. The pulsed Doppler gate was placed within the ductus venosus in all subjects. Color Doppler identified a turbulent flow velocity within the ductus venosus which was not present in the umbilical vein, hepatic vein or inferior vena cava. The ductus venosus pulsed Doppler waveform demonstrated flow velocity from the umbilical vein to the heart during ventricular systole, the rapid filling phase of ventricular diastole, and atrial systole. However, flow velocity was decreased during atrial systole compared to ventricular systole and the rapid filling phase of diastole. The ductus venosus index was computed from the Doppler waveform of the ductus venosus at points consistent with ventricular and atrial systole ((ventricular systole - atrial systole)/ventricular systole). Regression analysis demonstrated a significant (p = 0.001) relationship between the ductus venosus index and gestational age (ductus venosus index = 75.5757 - 7.25484 x weeks gestation), standard error of the estimate = 7.21959; R = -0.451. One fetus with a hypoplastic left atrium and ventricle demonstrated a normal ductus venosus index. Two fetuses, one with pulmonary atresia and the second with severe cardiovascular dysfunction, demonstrated an abnormal ductus venosus index associated with absent flow velocity during atrial systole. This was associated with notching in the umbilical vein. The ductus venosus index is an angle-independent measurement from which right ventricular preload may be evaluated.     

Normal values of fetal ductus venosus blood flow waveforms during the first stage of labor.

OBJECTIVE: To present normal values of fetal ductus venosus blood flow waveforms during the first stage of labor during and between contractions. MATERIALS AND METHODS: Seventy-eight women between the 37th and 41st weeks of gestation were included in the study. At distinct stages of cervical dilation, blood flow velocity waveforms of the fetal ductus venosus during and between contractions were visualized in fetuses with a normal non-stress test. The pulsatility index for veins, peak velocity index for veins and fetal heart rate were calculated off-line. The means +/- standard deviations (SD) during and between contractions were compared using the Wilcoxon test. RESULTS: Ductus venosus blood flow velocity waveforms were visualized during 331 contractions and 375 episodes of uterine quiescence in 74 of 78 fetuses (95%) during normal labor. The mean +/- standard deviation values of pulsatility and peak velocity indices for veins during contractions were 1.66 +/- 0.85 (median: 1.56, range: 0.29-4.69) and 1.46 +/- 0.65 (median: 1.34, range: 0.26-3.13), respectively. Between contractions the values were 0.48 +/- 0.19 (median: 0.46, range: 0.14-1.00) for the pulsatility index and 0.44 +/- 0.18 (median: 0.42, range: 0.14-1.00) for the peak velocity index for veins. These differences during and between contractions were highly significant (P-value < 0.0001), whereas the fetal heart rate showed no significant differences. CONCLUSION: There are significant differences in fetal ductus venosus blood flow waveforms during and between labor contractions. Further studies should evaluate whether these normal values of the fetal ductus venosus are beneficial for risk evaluation in fetuses with an abnormal non-stress test and/or intrauterine growth restriction.     

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.     

Reversed end-diastolic flow in the umbilical artery at 10-14 weeks of gestation is associated with absent pulmonary valve syndrome.

OBJECTIVE: To determine the incidence of reversed end-diastolic flow (REDF) in the umbilical artery in high-risk first-trimester pregnancies and evaluate associated conditions. METHODS: This was a prospective evaluation of the umbilical artery Doppler waveforms of 614 consecutive high-risk pregnancies between 10 and 14 weeks of gestation, to determine those with REDF. The associated anomalies and characteristics of these fetuses were then investigated. RESULTS: In 278/614 (45.3%) fetuses, there was positive end-diastolic flow in the umbilical artery; in 331/614 (53.9%) end-diastolic flow was absent and in 5/614 (0.8%) there was REDF. Three of the five fetuses with REDF had tetralogy of Fallot (TOF) with absent pulmonary valve syndrome (APVS) and a patent ductus arteriosus, and all three showed signs of cardiac failure, with reversed blood flow in the ductus venosus during atrial systole and generalized skin edema. Another fetus had a large ventricular septal defect and the remaining fetus had agenesis of the ductus venosus. Three fetuses had trisomy 18 and one had trisomy 13. CONCLUSIONS: REDF in the umbilical artery is very rare in early pregnancy and mostly occurs in association with major fetal vascular anomalies and cardiac defects, particularly TOF with APVS and patent arterial duct. We propose that the patency of the arterial duct in TOF with APVS leads to heart failure with subsequent demise early in pregnancy. Therefore, the frequent absence of the arterial duct observed in APVS in later pregnancy is more likely to be a result of early selection than a prerequisite for the development of this lesion as has been proposed previously.     

Reference ranges for fetal venous and atrioventricular blood flow parameters.

This cross-sectional study establishes reference ranges with gestation for Doppler parameters of fetal venous and atrioventricular blood flow. Color flow Doppler was used to examine 143 normal singleton pregnancies at 20-40 weeks' gestation. Flow velocity waveforms were recorded from the ductus venosus, right hepatic vein and inferior vena cava. The waveforms are triphasic, reflecting ventricular systole, early diastole and atrial contraction. Peak velocities for these parameters were measured with pulsed Doppler and a new index, the peak velocity index for veins (PVIV), was calculated. Similarly, time-averaged maximum velocities for the whole cardiac cycle were measured and the pulsatility index for veins (PIV) was calculated. Flow velocity waveforms were also recorded at the level of the atrioventricular valves and the ratios of peak velocities at early diastolic filling (E) and atrial contraction (A) were calculated. Regression analysis was used to define the association of each measured and calculated Doppler parameter with gestational age. Blood flow velocities in the fetal veins and velocities and E/A ratios across the atrioventricular valves increased significantly with gestation, whereas PVIV and PIV decreased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic vein, and PVIV and PIV were highest in the hepatic vein and lowest in the ductus venosus. In the ductus venosus, there was always forward flow throughout the heart cycle, whereas in the inferior vena cava and hepatic vein during atrial contraction, flow was away from or towards the heart or there was no flow. Pulsatility of flow velocity waveforms in the venous system is the consequence of changes in pressure difference between the venous system and the heart during the heart cycle. The finding that PVIV and PIV decrease with gestation is consistent with decreasing cardiac afterload and maturation of diastolic ventricular function.