Relationship between placental blood flow resistance and precordial venous Doppler indices

The role of the fetal biophysical profile in the management of fetal growth restriction

Growth-restricted fetuses are at risk of hypoxemia, acidemia, and stillbirth because of progressive placental dysfunction. Current fetal well-being, neonatal risks following delivery, and the anticipated rate of fetal deterioration are the major management considerations in fetal growth restriction. Surveillance has to quantify the fetal risks accurately to determine the delivery threshold and identify the testing frequency most likely to capture future deterioration and prevent stillbirth. From the second trimester onward, the biophysical profile score correlates over 90% with the current fetal pH, and a normal score predicts a pH >7.25 with a 100% positive predictive value; an abnormal score on the other hand predicts current fetal acidemia with similar certainty. Between 30% and 70% of growth-restricted fetuses with a nonreactive heart rate require biophysical profile scoring to verify fetal well-being, and an abnormal score in 8% to 27% identifies the need for delivery, which is not suspected by Doppler findings. Future fetal well-being is not predicted by the biophysical profile score, which emphasizes the importance of umbilical artery Doppler and amniotic fluid volume to determine surveillance frequency. Studies with integrated surveillance strategies that combine frequent heart rate monitoring with biophysical profile scoring and Doppler report better outcomes and stillbirth rates of between 0% and 4%, compared with those between 8% and 11% with empirically determined surveillance frequency. The variations in clinical behavior and management challenges across gestational age are better addressed when biophysical profile scoring is integrated into the surveillance of fetal growth restriction. This review aims to provide guidance on biophysical profile scoring in the in- and outpatient management of fetal growth restriction.

Evaluating the Effect of Pravastatin in Early-Onset Fetal Growth Restriction: A Nonrandomized and Historically Controlled Pilot Study

OBJECTIVE

This study aimed to analyze the effect of pravastatin on angiogenic factors, feto-maternal Doppler findings and pregnancy outcomes in women with early-onset fetal growth restriction (FGR) treated with pravastatin compared with nontreated controls.

STUDY DESIGN

This was a pilot study conducted between March 2016 and September 2017. Women with single pregnancies and FGR diagnosed at ≤ 28 weeks of gestation were offered 40 mg of pravastatin daily. Doppler progression, soluble fms-like tyrosine kinase 1 (sFlt-1)/placental growth factor (PlGF) values, and pregnancy outcomes were assessed and compared with consecutive historical controls. Controls were matched to treated women for gestational age, maternal characteristics, maternal and obstetric history, Doppler severity classification, and angiogenic factors at diagnosis. The sFlt-1/PlGF was measured in maternal serum at two different times: before pravastatin was started (ratio M0) and during pravastatin treatment (ratio M1). Doppler severity was classified into four categories: normal, mild, moderate, and severe.

RESULTS

A total of 38 women were enrolled in this study. No differences were observed in baseline characteristics between groups. However, when compared with the ratio M0, M1 was increased by a median (interquartile range) of 67.0 (-34.8 to 197.3) in the control group but decreased by a median (interquartile range) of -10.1 (-53.1 to -0.07) in the pravastatin treated group (p < 0.001). No significant differences were observed in Doppler progression throughout pregnancy. Median interval from diagnosis to delivery was extended by 16.5 days, the median newborn birthweight was increased from 1,040 to 1,300 g, and the number of women with preeclampsia decreased from 9 (47.4%) to 6 (31.6%) in treated women; however, these trends were not statistically significant.

CONCLUSION

In women with early-onset FGR, treatment with pravastatin 40 mg daily was associated with significant improvement in the angiogenic profile. Additionally, median pregnancy duration and median birthweight increased and the incidence of PE was reduced in treated women. Nevertheless, since this pilot study was underpowered, none of these differences were statistically significant.

KEY POINTS

· Pravastatin improves sFlt-1/PlGF in FGR.. · Pregnancy duration tended to be greater in treated women.. · Birthweight tended to be greater in treated women..

Reference values for fetal Doppler-based cardiocirculatory indices in monochorionic-diamniotic twin pregnancy

Background

Placental anastomoses in monochorionic diamniotic (MCDA) twin pregnancy have a major impact on fetal circulation. This study was designed to define reference ranges of cardiac and vascular Doppler indices in MCDA twin pregnancies.

Methods

This cross-sectional study included 442 uncomplicated MCDA twin fetuses undergoing Doppler ultrasonography at 18–35 weeks of gestation. Left and right myocardial performance index (LV-MPI, RV-MPI), E/A ratio of atrioventricular valves, pulsatility indices of umbilical artery, middle cerebral artery (MCA), and ductus venosus (DV), cerebroplacental ratio, peak systolic velocity of MCA, S/a ratio of DV, and early diastolic filling time of ductus venosus (DV-E) were evaluated under standardized settings. The equation models between Doppler indices and gestational age (GA) were fitted. After adjustment for GA, the correlations between MPI and fetal heart rate (FHR), and between MPI and DV indices were analyzed.

Results

Estimated centiles of Doppler indices were derived as a function of GA, being distinct in values from those of singletons. There was no correlation between GA-adjusted MPI and FHR. DV-E was inversely related to LV-MPI.

Conclusions

MCDA twins showed significant changes in some Doppler indices throughout gestation with quantitative differences from singletons, emphasizing the importance of MC twin-specific reference values for clinical application. Further adjustment of MPI for FHR was unnecessary. DV-E is a vascular index indirectly representing fetal diastolic function.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-04255-w.

Reference values for ductus venosus flow in normal gestation among an Egyptian population

Background

Doppler studies of the fetal circulation have demonstrated the importance of the ductus venosus in the continuous monitoring of fetuses, especially those of high-risk pregnancies that can lead to abnormal pregnancy outcome. We tried to put reference values for the normal ductus venosus (DV) flow in normal gestation to be used in further studies assessing the different pathologies.

Results

The DV length ranged from 9.8 to 20.9 mm, and the diameter ranged from 0.6 to 2.3 mm. The DV pulsatility index, resistive index, and systolic velocity/maximum velocity during atrial wave ratio declined linearly with increasing of gestational age and were increased after that during the last weeks of pregnancy. Ductus venosus S wave and A wave velocities increased linearly from a mean of 38.30 at the first trimester to 61.68 at the third trimester and from a mean of 11.38 at the first trimester to 30.71 at the third trimester respectively.

Conclusion

A reference range of the normal ductus venosus different Doppler parameters was constructed in a centile module.

Reference values for ductus venosus doppler indices of normal gestation at 22-37 weeks: A Vietnamese cohort study

Prenatal doppler ultrasound of the ductus venosus plays an important role in the evaluation of fetal circulation and fetal heart function. We aimed to establish the percentile of Resistivity Index (RI) and Pulsatility Index (PI) of the Ductus Venosus (DV) among normal Vietnamese fetuses with a gestation from 22 to 37 weeks in a cohort study. Normal Vietnamese fetuses with a gestation ranging from 22 to 37 weeks were examined in a cohort study. The PI and RI were recorded from the DV. We analyzed 640 participants who all fulfilled the inclusion and exclusion criteria of our study. Results: There was a significant correlation between RI, PI and gestational age as shown with the equations y = 0.077x - 0.003x² + 3.493e - 5x³ (r=0.97) and y = 0.106x - 0.004x² + 4.5e - 5x³ (r=0.94), respectively. A centile module was constructed for the DV RI and PI indices among normal Vietnamese fetuses with gestation from 22 to 37 weeks.

Impact of umbilical cord length on fetal circulatory system by Doppler assessment

INTRODUCTION

Numerous studies have revealed the impact of umbilical cord (UC) length on fetal perfusion; abundant data implicate abnormal UC length to neurological delay and subsequent poor prognoses for fetuses and newborns. Indeed, our group previously developed theoretical approximations that contributed to formulas capable of explaining the impact of UC length on cardiac output.

METHODS

We performed an observational study that measured the pulsatility index and flow velocity in umbilical arteries. A special Doppler measured proximal and distal indexes in both arteries. After birth, medical staff measured complete UC length. We obtained maternal and neonatal outcomes from clinical records.

RESULTS

Our study enrolled 20 pregnant mothers. We found that flow velocities in the two edges were different: fetal edges exhibited greater velocity in the majority of cases; but, when we compared pressure differentials (ΔP), the pulsatility index was significantly related to umbilical cord length.

CONCLUSIONS

Fetal perfusion, welfare, and viability are related to UC function as the conveyor of all fetal volemia. Excessive UC length affects cardiac dynamics and increases peripheral vascular resistance. Further studies could validate routine use of the differential proximal and distal measurements proposed in this article, and their implications in in utero fetal heart function. We also hope that early diagnosis or UC alterations could alert neonatologists and obstetricians to clinical conditions of the fetus.

First-trimester ductus venosus velocity ratio as a marker of major cardiac defects

OBJECTIVES

To examine ductus venosus (DV) flow in fetuses with and those without a cardiac defect and to evaluate different phases of DV flow in addition to the standard assessment of DV pulsatility index for veins (PIV) and the a-wave.

METHODS

This was a retrospective study of singleton pregnancies that underwent first-trimester ultrasound screening, which included DV flow assessment, at the University of Tübingen (between 2010 and 2017) or the University of Cologne (between 2013 and 2016). The study population comprised normal fetuses and fetuses with major cardiac defects at a ratio of 10:1. For each fetus, the following parameters of the DV waveform were evaluated: qualitative assessment of the a-wave, PIV measurement and ratios of flow velocities during the S-wave (S) or D-wave (D) and the a-wave (a) or v-wave (v). Reproducibility of DV-PIV and DV flow ratios was evaluated in 30 fetuses in which the DV flow was assessed twice.

RESULTS

Our study population included 480 anatomically normal fetuses and 48 with a cardiac defect. Median fetal nuchal translucency (NT) in the normal and in the affected group was 1.9 mm and 2.6 mm, respectively. In five (1.0%) of the normal and 18 (37.5%) of the affected cases, fetal NT thickness was above the 99^th centile. In the normal group, the DV a-wave was reversed in 15 (3.1%) cases and the DV-PIV was above the 95^th centile in 25 (5.2%). In the cases with cardiac defects, the a-wave was reversed and the DV-PIV measurement was above the 95^th centile in 26 (54.2%). The reproducibility of measurement of the ratios of DV flow velocities was similar to that of the DV-PIV. Most cardiac defects were associated with an abnormal a/S or a/D ratio. If the cut-off for these two ratios was set at the 5^th centile of the normal distribution, the detection rate of fetal cardiac anomalies would be 62.5%. This compares favorably with the DV-PIV, which detects 26 (54.2%) of the affected fetuses for the same threshold.

CONCLUSION

In the first trimester, the a/S ratio has the potential to detect approximately 60% of congenital cardiac defects for a false-positive rate of 5%. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Aortic isthmus shunt dynamics in normal and complicated monochorionic pregnancies

OBJECTIVE

To study fetal aortic isthmus (AoI) shunt dynamics in monochorionic (MC) twins.

METHODS

Normal and complicated MC pregnancies were prospectively enrolled. The relationship of isthmus flow index (IFI) with Doppler parameters of umbilical artery (UA), descending aorta, middle cerebral artery, and ductus venosus and with left and right ventricular cardiac output and stroke volume was studied.

RESULTS

The IFI was obtained in 180 examinations from 48 pregnancies (24 twin-twin transfusion syndrome, TTTS; 4 selective intrauterine growth restriction, sIUGR; 12 TTTS + sIUGR; and 8 uncomplicated). Median gestational age was 20.9 weeks. AoI diastolic flow was reversed in three cases. UA pulsatility index (PI) and ductus venosus-PI z-scores were negatively correlated with the IFI (r_s -0.40 and -0.26, respectively, p < 0.001). Regression analysis identified only UA-PI as a determinant of the IFI (p < 0.001). The IFI was significantly correlated with left ventricular cardiac output and stroke volume. It did not differ between TTTS donors and recipients. sIUGR fetuses had significantly lower IFI compared with normal-grown counterparts (p < 0.001).

CONCLUSION

In MC gestations, AoI shunting is predominantly determined by placental flow resistance, while cerebral impedance and volume status have no impact. In MC twins, the relationship between AoI flow and outcome deserves further study in the setting of sIUGR. © 2017 John Wiley & Sons, Ltd.

Ductus venosus blood flow velocity waveforms during the early second trimester of pregnancy in a Thai population

OBJECTIVE

To establish reference ranges for ductus venosus (DV) blood flow velocities and indices during the early second trimester.

METHODS

A cross-sectional DV Doppler study of fetuses at 15-22 weeks of gestation was conducted at Songklanagarind Hospital, Songkhla, Thailand, during 2013-2014. The peak forward velocities were recorded and the DV indices were calculated. Predicted reference ranges based on the 5th and 95th percentiles according to the week of gestation were constructed.

RESULTS

Among 371 fetuses, measurement of DV Doppler waveforms in the sagittal plane was achieved in 97.5% of cases. With advancing pregnancy (weeks 15 to 22), the DV velocities during ventricular systole, early diastole, and atrial contraction increased from 47.48 cm/s to 68.22 cm/s, 42.23 cm/s to 60.52 cm/s, and 15.94 cm/s to 34.84 cm/s, respectively. The time-averaged maximum value increased from 37.61 cm/s to 55.42 cm/s. The DV indices-pulsatility index for the vein, peak velocity index for the vein, preload index, and systolic/a-wave ratio-decreased from 0.79 to 0.59, 0.71 to 0.53, 0.63 to 0.47, and 2.72 to 1.90, respectively. The systolic/diastolic ratio remained relatively constant at 1.12.

CONCLUSIONS

Normal reference ranges for DV flow velocities and indices during the early second trimester were established.

Correlation analysis of ductus venosus velocity indices and fetal cardiac function

OBJECTIVE

To examine the relationships between the ductus venosus (DV) pulsatility index for veins (PIV), individual DV velocity ratios and diastolic and global myocardial cardiac function.

METHODS

Doppler measurements of the DV, atrioventricular (AV) valves and ventricular in- and outflow were analyzed. The DV-PIV and velocity ratios for individual phases (systole (S), end-systolic relaxation (v), early diastole (D), atrial systole (a), and S/v, S/D, S/a, v/D, v/a and D/a ratios) were calculated. The ratio of early and late diastolic peak velocities across AV valves was calculated (E/A ratio). Left modified myocardial performance index (MPI) was calculated from time intervals between valve clicks defining isovolumetric contraction/relaxation and ejection times. All values were transformed to Z-scores. The distributions of DV velocity ratios and DV-PIV were correlated with cardiac Doppler parameters.

RESULTS

A total of 1163 examinations from 213 fetuses, most of which were at risk for cardiac dysfunction, were included in the study. In 742 the PIV was normal and in 421 PIV was elevated > 2 SD above the normal mean. The DV-PIV correlated with velocity ratios (P < 0.0001) but not with E/A ratios and the MPI. S/v and v/D ratios were related to tricuspid and mitral E/A ratios and left ventricular MPI. The S/D ratio was only related to both E/A ratios. There was no relationship between a-wave-related velocity ratios and cardiac function.

CONCLUSIONS

Velocity ratios of the DV show relationships with cardiac function that are not reflected by the PIV alone. In cases of suspected fetal cardiac dysfunction based on elevated DV-PIV, analysis of velocity ratios or direct cardiac evaluation is suggested to determine the underlying pathophysiology.

Fetal venous circulation in monochorionic twin pregnancies with placental insufficiency: prediction of acidemia at birth or intrauterine fetal death

OBJECTIVES

To investigate fetal venous Doppler measurements in monochorionic twin pregnancies complicated by placental insufficiency and the relationship between fetal venous flow and acidemia at birth or intrauterine fetal death.

METHODS

This was a prospective study of 18 monochorionic twin pregnancies with placental insufficiency. Inclusion criteria were monochorionic-diamniotic twin pregnancy, abnormal umbilical artery (UA) Doppler indices, intact membranes and absence of fetal congenital abnormalities. Cases of twin-to-twin transfusion syndrome were excluded. The following Doppler measurements were studied: UA pulsatility index (PI), ductus venosus PI, middle cerebral artery PI and peak systolic velocity, intra-abdominal umbilical vein (UV) time-averaged maximum velocity (TAMXV) and left portal vein (LPV) TAMXV. Doppler parameters were transformed into Z-scores (SD values from the mean) or multiples of the median according to normative references.

RESULTS

UA pH < 7.20 occurred in nine (25.0%) neonates, pH < 7.15 in four (11.1%) and intrauterine death in four (11.1%) fetuses. The UV-TAMXV and LPV-TAMXV Z-scores were significantly lower in the group with pH < 7.20 or intrauterine fetal death (-1.79 vs -1.22, P = 0.006 and -2.26 vs -1.13, P = 0.04, respectively). In cases with pH < 7.15 or intrauterine fetal death, UV pulsations were more frequent (50.0% vs 10.7%, P = 0.03) and UV-TAMXV Z-score was significantly lower (-1.89 vs -1.26, P = 0.003). Mixed effects logistic regression analysis, accounting for the paired nature of the outcomes for the two twins in each pregnancy, demonstrated that the UV-TAMXV Z-score significantly predicted UA pH at birth < 7.20 or intrauterine fetal death. The Doppler parameter that independently predicted pH < 7.15 or intrauterine fetal death was presence of pulsation in the UV.

CONCLUSION

UV Doppler parameters may predict acidemia at birth or intrauterine fetal death in monochorionic twins complicated by placental insufficiency.

Reference ranges for ductus venosus velocity ratios in pregnancies with normal outcomes

OBJECTIVES

The purpose of this study was to establish reference ranges for ductus venosus velocity ratios.

METHODS

Singleton pregnancies from 11 to 38 weeks with exactly established gestational ages (GAs) were recruited for the study. Pregnancies with fetal anomalies, growth abnormalities, maternal medical complications, stillbirth, birth weight below the 10th or above the 90th percentile, and neonatal anomalies were excluded. The ductus venosus pulsatility index for veins (PIV) and velocity ratios (S/v, S/D, v/D, S/a, v/a, and D/a, where S indicates ventricular systole [s-wave], v, ventricular end-systolic relaxation [v-descent], D, passive diastolic ventricular filling [D-wave], and a, active ventricular filling during atrial systole [a-wave]) were calculated. Separate regression models were fitted to estimate the mean and standard deviation at each GA for each ratio.

RESULTS

A total of 902 velocity wave ratios and ductus venosus PIVs were used for reference ranges. The S/v, S/D, and v/D ratios were not changed with GA (P > .05 for all). The PIV and S/a, v/a, and D/a ratios were reduced with GA (P < .0001 for all). Significant reductions in the means and standard deviations of the PIV and S/a, v/a, and D/a ratios were observed between 17 and 18 weeks' gestation. Therefore, nomograms were separately created between 11 and 17 weeks and 18 and 38 weeks.

CONCLUSIONS

We created reference ranges for ductus venosus velocity ratios between 11 and 38 weeks' gestation in normal pregnancies. These reference ranges may prove beneficial for evaluation of fetal conditions that are associated with cardiovascular abnormalities.

Cord blood B-type natriuretic peptide levels in placental insufficiency: correlation with fetal Doppler and pH at birth

OBJECTIVE

To examine the correlation of cardiac B-type natriuretic peptide (BNP) concentrations in umbilical cord blood at birth with fetal Doppler parameters and pH at birth.

STUDY DESIGN

Prospective cross-sectional study with the following inclusion criteria: women with a singleton pregnancy, placental insufficiency characterized by increased pulsatility index (PI) of the umbilical artery (UA), intact membranes, and absence of fetal abnormalities. The exclusion criteria kept out cases of newborns with postnatal diagnosis of abnormality and cases in which the blood analysis was not performed. The Doppler parameters used were the UA PI, middle cerebral artery (MCA) PI, cerebroplacental ratio (CPR), and ductus venosus (DV) PI for veins (PIV), all converted into zeta scores. Blood samples were obtained from the umbilical cord immediately after delivery to measure the pH of the UA and the BNP.

RESULTS

Thirty-two pregnancies with placental insufficiency were included, 21 (65%) with positive diastolic flow and 11 (35%) with absent or reversed end diastolic flow in the UA. The concentration of BNP correlated significantly with the UA PI z-score (rho=0.43, P=0.016), the CPR z-score (rho=-0.35, P=0.048), the DV PIV z-score (rho=0.61, P<0.001), pH at birth (rho=-0.39, P=0.031), and gestational age (rho=-0.51, P=0.003). In the multiple regression analysis, antenatal parameters were included; the DV PIV z-score (P=0.008) was found to be an independent parameter correlating with BNP at birth. Correlation between BNP and the DV PIV z-score was borne out by the regression equation Log[BNP]=2.34+0.13*DV (F=18.8, P<0.001). Correlation between BNP and pH at birth was confirmed by the regression equation Log[BNP]=21.36-2.62*pH (F=7.69, P=0.01).

CONCLUSION

The results suggest that fetal cardiac dysfunction identified by BNP concentrations at birth correlated independently with changes in DV PIV and correlated negatively with pH values at birth.

Normal reference ranges of inferior vena cava doppler indices from 14 to 40 weeks of gestation

OBJECTIVE

To establish normal reference ranges of inferior vena cava (IVC) Doppler velocities in normal singleton pregnancies from 14 to 40 weeks.

METHODS

A prospective descriptive study was conducted on normal singleton pregnancies with confirmed gestational age. The sonographic measurements of IVC Doppler indices, including preload index, peak velocity index for vein, and pulsatility index for vein, were determined by experienced sonographers.

RESULTS

A total of 645 measurements were performed, ranging from 12 to 30 measurements available for each gestational week. The relationship between gestational age and IVC Doppler indices was not linear. The best-fitted regression equations for the indices are as follows: [Formula: see text] [Formula: see text] [Formula: see text] (GA = gestational age in week) All IVC Doppler indices rapidly declined from 14 to 20 weeks of gestation and then they were relatively constant or slightly decreased throughout the rest of pregnancy. The tables of normal reference ranges were constructed.

CONCLUSIONS

Normal reference ranges of IVC Doppler indices for each gestational week from 14 to 40 weeks were constructed. This normative data may be a useful noninvasive tool in evaluation of fetal cardiac function.

Normal reference ranges of ductus venosus Doppler indices in the period from 14 to 40 weeks' gestation

OBJECTIVE

To construct reference ranges of ductus venosus (DV) Doppler indices in normal singleton pregnancies.

METHODS

A cross-sectional study was conducted on low-risk singleton pregnancies with accurate gestational age, and normal fetuses were enrolled into the study. Measurements of DV Doppler indices were determined by experienced sonographers. Poor quality images were excluded.

RESULTS

A total of 640 fetuses underwent DV measurements, ranging from 13 to 30 for each gestational week. The relationship between gestational age and DV Doppler indices was not linear. The best-fit regression equations are as follows: preload index = (5.061 - 0.4882) × exp (-0.211 × GA) + 0.4882; peak velocity index for veins = (7.498 - 0.5609) × exp (-0.2184 × GA) + 0.5609; pulsatility index for veins = (17.9 - 0.6053) × exp (-0.2512 × GA) + 0.6053; systolic/atrial wave ratio = (300 - 2.124) × exp (-0.3649 × GA) + 2.124. Notably, during the period from 14 to 20 weeks' gestation, all of the four indices rapidly decreased and they were relatively stable or slightly decreased after that. The nomogram tables for various percentile ranges were constructed.

CONCLUSION

A nomogram for DV Doppler indices for each gestational week during the period from 14 to 40 weeks' gestation was established. These reference ranges may be a useful non-invasive tool for evaluation of fetal cardiac function.

Venous Doppler evaluation of the growth-restricted fetus

Evaluation of venous Doppler parameters has significantly contributed to the understanding of the vascular mechanisms that lead to fetal growth restriction (FGR) and subsequent fetal deterioration in the setting of progressive placental dysfunction. Venous redistribution of umbilical venous blood flow away from the fetal liver precedes fetal growth delay. Venous Doppler examination allows adjustment of monitoring intervals in recognition of accelerating fetal deterioration. The timing of delivery in early-onset FGR remains challenging because gestational age has an overriding effect on the neonatal outcome until the late second trimester and randomized trials of specific delivery triggers are lacking.

Venous Doppler studies in low-output and high-output hydrops fetalis

OBJECTIVE

The objective of the study was to compare fetal venous Doppler flow reflecting cardiac function in fetuses with hydrops fetalis between a group of congenital heart defect (low cardiac output) and a fetal anemia group (high cardiac output).

STUDY DESIGN

This was a prospective cross-sectional analysis. It was conducted at the Maharaj Nakorn Chiang Mai Hospital, Tertiary center, Medical School. The study included fetuses with hydrops fetalis secondary to cardiac causes (low output group) and anemia (high output group). All fetuses underwent ultrasound examination to assess ductus venosus (DV) and umbilical vein (UV) Doppler indices. The results were related to normal reference range and were also compared between the group of high-output and the low-output group.

RESULTS

Sixty-nine hydropic fetuses were available for analysis, 50 in the high-output group and 19 in the low-output group. The peak velocity index, preload index, and the pulsatility index of the DV were significantly low in the high-output group, whereas they were significantly high in the low-output group. The umbilical vein pulsations were found in 78.9% of the fetuses with low-output hydrops fetalis but only 28.0% of fetuses in the high output group (P < .001).

CONCLUSION

New insights gained from this study are that hydrops caused by severe anemia because of hemoglobin Bart's is not associated with high central venous pressures as is seen in hydropic fetuses with coronary heart disease. This suggests that cardiac decompensation is not the primary mechanism of hydrops in these anemic fetuses. Additionally, umbilical vein pulsations are not a sign of cardiac failure in the anemic group.

Twin-to-twin transfusion syndrome: a comprehensive update

Twin-to-twin transfusion syndrome (TTTS) is a serious complication in about 10% to 20% of monozygous twin gestations with an incidence of 4% to 35% in the United States. Severe TTTS is reported to occur in 5.5% to 17.5% of cases. TTTS is a progressive disease in which sudden deteriorations in clinical status can occur, leading to death of a co-twin. Up to 30% of survivors may have abnormal neurodevelopment as a result of the combination of profound antenatal insult and the complications of severe prematurity. This article presents an overview of what is known about the pathophysiology and the diagnosis of TTTS, the role of echocardiography in TTTS, treatment options available for TTTS, complications of treatment for TTTS, and short- and long-term outcomes of TTTS.

Umbilical venous volume flow in twin-twin transfusion syndrome

OBJECTIVES

To examine umbilical venous volume flow (UVF) dynamics by twin status and disease severity in untreated twin-twin transfusion syndrome (TTTS).

METHODS

In 70 cases of untreated TTTS, absolute UVF, UVF corrected for estimated fetal weight (UVF/kg), intertwin difference (DeltaUVF/kg) and recipient to donor ratio (R/D-UVF/kg) were calculated. Parameters for UVF were compared with respect to twin status and disease severity (early, Quintero Stages I and II; advanced, Stages III and IV).

RESULTS

UVF/kg was higher in recipients than in donors and decreased with advancing stage in both twins (in recipients, 183.9 mL/kg/min vs. 145.6 mL/kg/min, P = 0.043; in donors, 137.5 mL/kg/min vs. 122.5 mL/kg/min, P = 0.033). Linear regression analysis demonstrated that the overall best correlation coefficient for DeltaUVF/kg was obtained for the Doppler pulsatility index of the umbilical artery (t = - 4.536, P < 0.001). In advanced stage, absolute and weight-corrected UVF were lower overall, while significant differences in intertwin volume flows persisted. The lowest flows were observed in hydropic recipients (median, 67.0 (range, 55.2-122.0) mL/kg/min vs. 180.8 (range, 59.1-565.4) mL/kg/min; P = 0.001).

CONCLUSIONS

In TTTS, UVF is significantly higher in recipients than in donors. With progression to advanced stage UVF/kg decreases in both twins as the magnitude of UVF that can be accommodated by the recipient declines. Further study of these dynamics in combination with cardiac performance parameters is warranted to refine diagnostic and prognostic assessment.

Ultrasound of the placenta: a systematic approach. Part II: functional assessment (Doppler)

Doppler velocimetry is the ideal clinical tool to assess placental performance in high-risk pregnancies. It also has value in predicting later complications and outcome in pregnancies which appear uncomplicated. All three circulations (fetal, placental and maternal) may be interrogated by Doppler technology. In the following review, we present basic physics aspects of Doppler and discuss mainly Doppler investigation of the fetal-placental circulation (umbilical artery, intraplacental circulation) as well as the uterine arteries. The assessment of umbilical blood flow provides information on blood perfusion of the fetal-placental unit. The diastolic blood flow velocity component in umbilical artery increases with advancing gestation. In pregnancies complicated by placental dysfunction, there may be a reduction in the number of functional villi and/or small blood vessels with, as a result, increased impedance, reflected, mainly, by a decrease in end-diastolic velocity. When the resistance increases even more, there is no diastolic forward velocity (absent end-diastolic velocity). Further increase in the resistance causes reversed end-diastolic velocity, which is considered a late step in the cascade of events leading to intrauterine fetal demise. Doppler assessment of the umbilical arteries was found to improve outcome of high-risk pregnancies, and reduce hospital admissions. On the contrary, routine Doppler ultrasound in low risk or unselected populations does not seem to confer benefit on mother or newborn. Uterine artery Doppler is a useful test in predicting pregnancies at high risk of developing complications related to uteroplacental insufficiency. It identifies women who may benefit from increased antenatal surveillance or prophylactic therapy. Three-dimensional power Doppler sonography can provide new insights into placental pathophysiology.

Doppler Assessment of the Intrauterine Growth-Restricted Fetus

The evaluation of fetal well-being by Doppler velocimetry in cases of intrauterine growth restriction (IUGR) is of great importance as it is very useful in detecting those IUGR fetuses that are at high risk because of hypoxemia. Several Doppler studies initially on fetal arteries and recently on the fetal venous system provide valuable information for the clinicians concerning the optimal time to deliver. Doppler sonography in combination with the other biophysical methods such as cardiotocogram and biophysical profile score should be used in everyday practice for the monitoring and appropriate management of the growth-restricted fetuses. The purpose of this review is to describe the current approaches in Doppler assessment of IUGR fetal circulation.

Venous-arterial Doppler ratios in the prediction of acidemia at birth in pregnancies with placental insufficiency

OBJECTIVES

Investigate the prediction of birth acidemia in pregnancies with placental insufficiency using two newly created venous-arterial Doppler ratios: pulsatility index (PI) of the ductus venosus (DV) over PI of the middle cerebral artery (MCA) and PI of the DV over PI of the umbilical artery and establish cut-off values for this prediction.

METHODS

This was a prospective cross-sectional study involving 47 patients with placental insufficiency managed in two Brazilian hospitals. All pregnancies were singleton, over 26 weeks of age and without structural or chromosome anomalies. A ROC curve was calculated for the venous-arterial ratios (independent variable) and acidemia (dependent variable).

RESULTS

The DV/AU PI ratio was not a good predictor of acidemia at birth. The DV/MCA PI ratio was related to fetal acidemia (area under the ROC curve 0.785, p = 0.004). The cut-off value was 0.582, sensibility 66.7%, specificity 77.1% and accuracy 74.5%.

CONCLUSIONS

The DV/MCA PI ratio is adequate for the diagnosis of acidemia at birth in pregnancies with placental insufficiency. The cut-off value was 0.582.

Venous Doppler in the assessment of fetal cardiovascular status

PURPOSE OF REVIEW

The purpose of this review is to highlight recent developments in the Doppler assessment of the fetal venous circulation with special reference to clinical applications in the human fetus.

RECENT FINDINGS

Doppler evaluation of the fetal venous circulation has increased our understanding of fetal cardiovascular function. Examples include the regulatory role of the ductus venosus in fetal nutrient partitioning and the significance of venous and arterial circulatory watershed areas. Alterations in cardiac afterload, contractility compliance, intravascular volume status and heart rate modulate venous and arterial flow velocity waveforms. Concurrent examination of these cardiovascular factors is of great importance in fetal growth restriction, complicated monochorionic multiple gestation, fetal hydrops and arrhythmia. In these conditions, comprehensive Doppler assessment provides critical diagnostic and prognostic information and has a key role in directing interventions.

SUMMARY

Venous Doppler has added a critical dimension to the understanding of fetal cardiovascular pathophysiology. In both health and disease, venous Doppler must now occupy a fundamental position in the comprehensive assessment of the fetal circulation.

Toward quantitative fetal heart rate monitoring

Continuous electronic fetal heart rate (FHR) monitoring during labor is motivated by the clinical experience that fetal distress causes loss of FHR variation and the occurrence of decelerations late during uterine contraction. This practice is of uncertain clinical benefit, perhaps because the interpretation is qualitative. We have developed new quantitative measures and analyzed cardiotocograph records from 148 consecutive patients, 44 of whom had at least one "nonreassuring" epoch. In multivariate regression models, measures of deceleration and variability were significantly associated with the obstetrician's diagnosis (receiver operating characteristic area 0.84, p < 0.05). This approach may be useful clinically.

Intrauterine hemodynamic change in TTTS: the alterations in the inferior vena cava waveform in the donor fetus

BACKGROUND

Significant hemodynamic changes are commonly observed in both fetuses in twin-twin transfusion syndrome.

METHODS AND RESULTS

We describe two donor fetus cases in twin-twin transfusion syndrome associated with abnormal waveform patterns in the inferior vena cava after therapeutic amnioreduction. Subsequent echocardiographic examinations demonstrated progressive deterioration of the cardiac function in the recipient fetuses.

CONCLUSIONS

We suggest that alterations in the inferior vena cava waveform in the donor fetuses may contribute to the accurate prediction of deterioration in fetal circulation after amnioreduction.

Venous Doppler in the prediction of acid-base status of growth-restricted fetuses with elevated placental blood flow resistance

OBJECTIVE

This study was undertaken to test which venous Doppler parameter offers the best prediction of acid-base status at birth in pregnancies complicated by intrauterine growth restriction (IUGR) caused by placental dysfunction.

STUDY DESIGN

A prospective cross-sectional Doppler study of IUGR fetuses with abnormal umbilical artery Doppler and birth weight less than the 10th percentile. Absence of atrial systolic forward velocities in the ductus venosus (DV) (DV-RAV) and umbilical vein (UV) pulsations were noted and multiple venous indices were calculated for the inferior vena cava (IVC) and DV (IVC and DV preload index, peak velocity index [PVIV] and pulsatility index [PIV] and the DV S/a ratio). Doppler indices, UV pulsations, and DV- RAV were related to an umbilical artery cord pH <7.20, and a pH <7.00 and/or base deficit greater than -13 (severe metabolic compromise) in neonates delivered by cesarean section without labor.

RESULTS

In 122 fetuses all venous Doppler indices were equally predictive of a pH <7.20, with the exception of the IVC PVIV. No Doppler index predicted severe metabolic compromise. Bayesian analysis of individual Doppler parameters showed comparable outcome prediction with the highest sensitivity for the IVC PIV (76%) and the highest specificity for DV-RAV (96%). Combined assessment of the IVC, DV, and UV provided the most accurate outcome prediction. Doppler abnormality in either vessel identified 89% of neonates with pH <7.20 (negative predictive value 92%) and 10 of 11 neonates with severe metabolic compromise. Prediction was most specific (84%) when Doppler parameters were abnormal in all 3 vessels.

CONCLUSION

IVC, DV, and UV Doppler parameters correctly predict acid-base status in a significant proportion of IUGR neonates. Combination, rather than single vessel assessment provides the best predictive accuracy. While the choice of Doppler index can be guided by operator preference, familiarity with the examination technique of all 3 vessels is encouraged to offer the highest flexibility in clinical practice.