Measurement of venous blood flow in the human fetus: a dream comes true, but now for some standardization

Comment on Barbieri et al. Umbilical Vein Blood Flow in Uncomplicated Pregnancies: Systematic Review of Available Reference Charts and Comparison with a New Cohort. J. Clin. Med. 2023, 12, 3132

We would like to comment on the systemic review article published in the Journal of Clinical Medicine by Barbieri et al [...].

The Fetal Liver Afferent Venous Flow Volumes in Fetuses With Appropriate for Gestational Age Birth Weight

OBJECTIVES

The present study aimed: 1) to simultaneously investigate the relationship between blood flow volumes of the two fetal liver afferent venous systems of normally appropriate for gestational age newborns. 2) to establish the normal reference range centiles values that will serve as a basis for future investigations.

METHODS

A cross-sectional, prospective study of singleton low obstetric risk pregnancies. Doppler examination included the measurement of the umbilical and the main portal vein vessels' diameters and time-averaged maximum velocity. The absolute and per kilogram of estimated fetal weight flow volumes and the ratio between the placental and portal blood volume flow were calculated from these data.

RESULTS

Three hundred and sixty-three pregnant women were included in the study. The umbilical and portal flow volumes' capacity to provide blood flow per kilogram of fetal weight, in the period of maximum fetal growth, was diverse. The placental flow decreased continuously from a mean of 121.2 mL/min/kg at the 20th week of gestation to 64.1 mL/min/kg at the 38th week of gestation. Meanwhile, the portal flow volume per kilogram of fetal weight increased from 9.6 mL/min/kg at 32 weeks of gestation to 10.3 at the 38th week of gestation. This resulted in a decrease in the umbilical to portal flow volume ratio from 13.3 to 9.6 during this period.

CONCLUSION

Our results indicate that in the period of maximum fetal growth, the placental/portal ratio diminishes emphasizing the portal flow's predominance with low oxygen and nutrient supply to the liver.

Prediction of late-onset fetal growth restriction by umbilical artery velocities at 37 weeks of gestation: a cross-sectional study

OBJECTIVE

To explore the predictive capacity of umbilical artery (UA) velocities at 37 weeks of gestation in identifying fetal growth restriction (FGR).

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

We retrospectively recruited 569 fetuses in the study. Thirty-nine FGR infants and 57 small-for-gestational-age (SGA) infants with normal UA Doppler at 37 weeks, as the study groups and 473 adequate-for-gestational-age (AGA) infants as a control group in a tertiary referral centre.

METHODS

All the parameters of UA velocities, including the UA end-diastolic velocity (UA-EDV), UA peak systolic velocity (UA-PSV), UA mean diastolic velocity (UA-MDV) and UA time-averaged maximum velocity (UA-TAMXV), and UA Doppler were measured at approximately 37 weeks of gestation.

RESULTS

Among the FGR, SGA and AGA groups, the UA-MDV, UA-TAMXV, UA-PSV and UA-EDV decreased with the loss of fetal weight. Multivariate logistic regression analyses showed that the UA-TAMXV was an independent predicting factor of FGR. It had a moderate predictive value for FGR. The area under the receiver operating characteristic curve was 0.82 (95% CI: 0.79 to 0.85).

CONCLUSIONS

The UA velocities decreased with the loss of fetal weight among the FGR, SGA and AGA groups and the UA-TAMXV was independently predictive of FGR. The results suggest that the UA-TAMXV might be a new parameter to predict FGR prior to delivery.

Comparison of Variations Between Spectral Doppler and Gaussian Surface Integration Methods for Umbilical Vein Blood Volume Flow

OBJECTIVES

We are studying a new method for estimating blood volume flow that uses 3-dimensional ultrasound to measure the total integrated flux through an ultrasound-generated Gaussian surface that intersects the umbilical cord. This method makes none of the assumptions typically required with standard 1-dimensional spectral Doppler volume flow estimates. We compared the variations in volume flow estimates between techniques in the umbilical vein.

METHODS

The study was Institutional Review Board approved, and all 12 patients gave informed consent. Because we had no reference standard for the true umbilical vein volume flow, we compared the variations of the measurements for the flow measurement techniques. At least 3 separate spectral Doppler and 3 separate Gaussian surface measurements were made along the umbilical vein. Means, standard deviations, and coefficients of variation (standard deviation/mean) for the flow estimation techniques were calculated for each patient. P < .05 was considered significant.

RESULTS

The ranges of the mean volume flow estimates were 174 to 577 mL/min for the spectral Doppler method and 100 to 341 mL/min for the Gaussian surface integration (GSI) method. The mean standard deviations (mean ± SD) were 161 ± 95 and 45 ± 48 mL/min for the spectral Doppler and GSI methods, respectively (P < .003). The mean coefficients of variation were 0.46 ± 0.17 and 0.18 ± 0.14 for the spectral Doppler and GSI methods respectively (P < 0.002).

CONCLUSIONS

The new volume flow estimation method using 3-dimensional ultrasound appears to have significantly less variation in estimates than the standard 1-dimensional spectral Doppler method.

The role of umbilical artery velocities in the clinical assessment of twin-twin transfusion syndrome at stage

OBJECTIVE

To analyze the discordances of the umbilical artery velocities between pregnancies with twin-twin transfusion syndrome (TTTS) at stage I and those with normal monochorionic-diamniotic (MCDA) twins, and investigate the value of their discordances in predicting TTTS at stage I.

METHODS

We recruited 58 twin pregnancies with TTTS at stage I and 60 normal MCDA twin pregnancies in a tertiary referral center retrospectively. The umbilical artery velocities and their discordances were compared between the normal and TTTS twins.

RESULTS

The discordances of umbilical artery mean diastolic velocity (UA-MDV), umbilical artery time-averaged maximum velocity (UA-TAmax), umbilical artery peak systolic velocity (UA-PSV), and umbilical artery end-diastolic velocity (UA-EDV) were higher in the TTTS group than in the normal group. In TTTS co-twins, the UA-MDV, UA-TAmax, UA-PSV, and UA-EDV in recipients were higher than those in donors. The discordances of UA-TAmax and UA-PSV were found to be independent predicting factors for TTTS at stage I.

CONCLUSION

Co-twin umbilical artery velocity discordances were significantly associated with stage I TTTS. The results suggest that UA-TAmax and UA-PSV might be new parameters for predicting TTTS at stage I.

Evaluation of Umbilical Vein Blood Volume Flow in Preeclampsia by Angle-Independent 3D Sonography

OBJECTIVES

To investigate the association between umbilical vein blood volume flow and the condition of preeclampsia in an at-risk maternal patient cohort. Umbilical vein volume flow was quantified by a 3-dimensional (3D) sonographic technique that overcomes several limitations of standard sonographic flow measurement methods.

METHODS

A total of 35 patients, each with a singleton pregnancy, were recruited to provide 5 patients with preeclampsia, derived as a subset from a 26-patient at-risk group, and 9 patients with normal pregnancies. An ultrasound system equipped with a 2.0-8.0-MHz transducer was used to acquire multivolume 3D color flow and power mode data sets to compute the mean umbilical vein volume flow in patients with normal pregnancies and preeclampsia.

RESULTS

The gestational ages of the pregnancies ranged from 29.7 to 34.3 weeks in the patients with preeclampsia and from 25.9 to 34.7 weeks in the patients with normal pregnancies. Comparisons between patients with normal pregnancies and those with preeclampsia showed weight-normalized flow with a moderately high separation between groups (P = .11) and depth-corrected, weight-normalized flow with a statistically significant difference between groups (P = .035). Umbilical vein volume flow measurements were highly reproducible in the mean estimate, with an intrapatient relative SE of 12.1% ± 5.9% and an intrameasurement relative SE of 5.6% ± 1.9 %. In patients who developed pregnancy-induced hypertension or severe pregnancy-induced hypertension, umbilical vein volume flow suggested gestational hypertensive disorder before clinical diagnosis.

CONCLUSIONS

Results indicate that mean depth-corrected, weight-normalized umbilical vein volume flow is reduced in pregnancies complicated by preeclampsia and that volume flow may indicate hypertensive disorder earlier in gestation. Volume flow measurements are highly reproducible, and further study in a larger clinical population is encouraged to determine whether 3D volume flow can complement the management of preeclampsia and, in general, at-risk pregnancy.

Modelling umbilical vein blood flow normograms at 14-40 weeks of gestation by quantile regression analysis

OBJECTIVE

To construct reference limits for gestation of umbilical vein blood flow (UVBF) in normal singleton pregnancies between 14 and 40 weeks of gestation using quantile regression.

METHODS

We ultrasonographycally examined 852 fetuses from low-risk pregnancies between 16 and 40 weeks of gestation in a prospective cross-sectional study. UV diameter and time-averaged maximum velocity (TAMXV) were measured in UV intra-abdominal portion by real time and Doppler ultrasonography. A semi-automatic measurement software was used to obtain UV diameter values. UVBF was then calculated from UV diameter and TAMXV measurements and expressed both as absolute value and as value normalized for fetal abdominal circumference (UVBF/AC). Individual centile values of the variables investigated were established by quantile regression in the gestational interval considered. In 50 cases UVBF was measured twice by the same investigator or by a second investigator and the intra- and inter-observer agreement were calculated.

RESULTS

A significant increase in UV diameter, TAMXV, UVBF absolute value and UVBF/AC was evidenced in the gestational period considered. Growth charts were established based on these measurements. The intra- and inter-observer intraclass correlation coefficients resulted as 0.92 (0.87-0.96) and 0.89 (0.84-0.97), respectively, for UBVF.

CONCLUSIONS

In this study we constructed UVBF charts using quantile regression in a large cohort of low-risk pregnancies. These charts offer the advantage of specific estimated regression parameters for each percentile, better defining the normal range of UVBF. This promises to be useful in the diagnosis and management of fetuses with abnormal fetal growth.

Three-dimensional sonographic measurement of blood volume flow in the umbilical cord

OBJECTIVES

Three-dimensional (3D) umbilical cord blood volume flow measurement with the intention of providing a straightforward, consistent, and accurate method that overcomes the limitations associated with traditional pulsed wave Doppler flow measurement and provides a means by which to recognize and manage at-risk pregnancies.

METHODS

The first study involved 3D sonographic volume flow measurements in 7 healthy ewes whose pregnancies ranged from 18 to 19 weeks' gestation (7 singletons). Sonographic umbilical arterial and venous flow measurements from each fetus were compared to the corresponding average measured arterial/venous flow to assess the feasibility of measurement in a static vessel. A second complementary study involved 3D sonographic volume flow measurements in 7 healthy women whose pregnancies ranged from 17.9 to 36.3 weeks' gestation (6 singletons and 1 twin). Umbilical venous flow measurements were compared to similar flow measurements reported in the literature. Pregnancy outcomes were abstracted from the medical records of the recruited patients.

RESULTS

In the fetal sheep model, arterial/venous flow comparisons yielded errors of 10% or less for 8 of the 9 measurements. In the clinical study, venous flow measurements showed agreement with the literature over a range of gestational ages. Two of the 7 patients in the clinical study had lower flow than anticipated for gestational age; one had a subsequent diagnosis of intrauterine growth restriction, and the other had preeclampsia.

CONCLUSIONS

Accurate measurement of umbilical blood volume flow can be performed with relative ease in both the sheep model and in humans using the proposed 3D sonographic flow measurement technique. Results encourage further development of the method as a means for diagnosis and identification of at-risk pregnancies.

Pre-sampling ultrasound evaluation and assessment of the tissue yield during sampling improves the diagnostic reliability of office endometrial biopsy

We evaluated the implementation of a strict procedure for endometrium biopsy, including pre-sampling ultrasound examination and assessment of the tissue yield during sampling, in 257 consecutive women with abnormal bleeding. The tissue yield was assessed during sampling and scored from 1 to 4. The median endometrial thickness as measured by ultrasound was 5.0 mm, 5.1 mm, 10.0 mm and 18.7 mm for a tissue yield score of 1, 2, 3 and 4, respectively. The median endometrial thickness at ultrasound and the median tissue yield score was 18.3 mm and score 4 in the endometrial cancer cases, compared with 3.9 mm and score 1, and 14.8 mm and score 3 in the case of endometrial atrophy and hyperplasia, respectively; and 11.5 mm and score 2 in endometrial polyp cases. Overall, 12 cancers were diagnosed. No endometrial cancer was diagnosed during follow-up (median 447 days). A strict office endometrial biopsy procedure contributes to the diagnostic reliability for intracavitary pathology.

Umbilical vein blood flow at 11 + 0 to 13 + 6 weeks of gestation

OBJECTIVE

To establish reference intervals for fetal umbilical vein (UV) diameter, UV time averaged maximum velocity (TAMXV) and UV flow (UVBF) at 11 + 0 to 13 plus; 6 weeks of gestation and to determine the intraobserver reliability of these measurements.

METHODS

We considered, in a cross-sectional study, 162 fetuses from uncomplicated singleton pregnancies at 11 + 0 to 13 + 6 weeks of gestation. UV diameter and TAMXV were measured in its intraabdominal portion by real-time and Doppler ultrasonography and UVBF calculated. Relationships between these parameters and fetal crown rump length were tested by regression analysis. In 25 cases UVBF was measured twice by the same investigator and the intraobserver agreement of these measurements was calculated.

RESULTS

A significant increase was evidenced in the gestational age period considered in UV diameter (r = 0.729, p < 0.0001), TAMXV (r = 0.691, p < 0.0001) and UVBF (r = 0.777, p < 0.0001). UVBF increased from 2.26 ml/min at 11 weeks to 15.62 ml/min at 13 + 6 weeks of gestation. The intraobserver ICCs were 0.96, 0.92 and 0.88, respectively, for UV diameter, TAMXV and UVBF.

CONCLUSIONS

In normal fetuses, UV diameter, TAMVX and flow increase between 11 + 0 and 13 + 6 weeks of gestation. In this gestational age interval, the calculation of UV blood flow and its components shows an intraobserver agreement reliable enough for clinical use.

Agreement between umbilical vein volume blood flow measurements obtained at the intra-abdominal portion and free loop of the umbilical cord

OBJECTIVE

The umbilical vein (UV) is a single vessel and theoretically the volume of blood flowing through it should be equal whether it is measured at the intra-abdominal portion (IA) or a free loop of the umbilical cord (FL). However, the reported values vary considerably depending on the technique and site of measurement. Our objective was to investigate the correlation and agreement between UV volume blood flows (Q(uv)) measured at the IA and FL.

METHODS

Blood flow velocities and inner diameter of the UV were measured cross-sectionally at the IA and FL in 131 pregnant women at 22-24 weeks' gestation, and in 53 of them longitudinally at 4-weekly intervals until delivery. For each sampling site, the Q(uv) was calculated as: 0.5 x time-averaged maximum velocity x pi x (UV diameter/2)(2).

RESULTS

The mean Q(uv) measured at the IA (61.5 +/- 23.3 mL/min) and FL (60.7 +/- 17.6 mL/min) cross-sectionally in 131 fetuses at 22-24 weeks of gestation were similar, but the bivariate correlation between them was not strong (r = 0.38; P < 0.0001) and the intraclass correlation coefficient (ICC) was 0.37 (95% CI, 0.21-0.51). When the agreement between 131 pairs of Q(uv) measurements was tested with Bland-Altman analysis, the mean of the ratio IA-Q(uv)/FL-Q(uv) was found to be 1.05 (i.e. IA-Q(uv) exceeded FL-Q(uv) on average by 5%) with 95% limits of agreement of 0.31-1.78. In the longitudinal analysis of 232 pairs of Q(uv) measurements from 53 fetuses at 22-40 weeks, the mean Q(uv) obtained at the IA and FL were similar, i.e. 164 +/- 87 (range, 25-484) mL/min vs. 159 +/- 82 (range, 30-470) mL/min, and the correlation between them, assessed after grouping the observations in five different gestational age groups of 4-week intervals, was slightly better (r = 0.45-0.62; P < 0.0001). The ICC for the Q(uv) measurements obtained at the two sites ranged from 0.38 to 0.54. The mean of the ratio IA-Q(uv)/FL-Q(uv) was 1.07 (i.e. IA-Q(uv) exceeded FL-Q(uv) on average by 7%), with 95% limits of agreement of 0.39-1.75.

CONCLUSION

Average Q(uv) measured at the IA and FL was similar, but the agreement between individual pairs of measurements was not good enough to be able to use them interchangeably. Therefore, any clinical application of Q(uv) measurement would require standardization of the technique, strict adherence to methodology and use of appropriate reference ranges for it to be useful.

Doppler-derived umbilical artery absolute velocities and their relationship to fetoplacental volume blood flow: a longitudinal study

OBJECTIVES

To construct reference ranges for serial measurements of the umbilical artery (UA) absolute blood flow velocities in the second half of pregnancy and to test the hypothesis that significant associations exist between UA velocities and placental volume blood flow assessed from umbilical vein blood flow velocities and diameter.

METHODS

This was a prospective longitudinal study of the umbilical circulation. UA absolute velocities and umbilical vein blood flow were measured at 4-weekly intervals between 19 and 42 weeks' gestation in 130 low-risk singleton pregnancies. A total of 511 observations were used to construct the reference ranges and assess the association between UA absolute velocities and placental volume flow using multilevel modeling.

RESULTS

Both UA absolute velocities and placental volume blood flow showed a steady increase throughout the second half of pregnancy. However, the gestational age-related increase in the UA end-diastolic velocity (EDV) was greater than the corresponding increase in the peak systolic velocity (PSV). The time-averaged intensity-weighted mean velocity (TAWMV)/time-averaged maximum velocity (TAMXV) was 0.6 indicating probably not a completely parabolic velocity profile. There was a significant positive association (P < 0.00001) between UA absolute velocities and placental volume blood flow, but this association was modified by the gestational age. The intraobserver coefficients of variation for the UA PSV, EDV, TAMXV and TAWMV and placental volume blood flow were 10.17%, 16.29%, 11.46%, 18.18% and 8.61%, respectively.

CONCLUSION

We have established new reference ranges for the UA absolute velocities based on longitudinal data. They show a significant association with fetoplacental volume blood flow and may have a clinical value in the assessment of the umbilical circulation.

Reference ranges for umbilical vein blood flow in the second half of pregnancy based on longitudinal data

OBJECTIVES

To construct new reference ranges for serial measurements of umbilical vein (UV) blood flow.

METHODS

Prospective longitudinal study of blood flow velocities and diameter of the UV measured at four-weekly intervals during 19 to 42 weeks' gestation in 130 low-risk singleton pregnancies. Regression models and multilevel modeling were used to construct the reference ranges.

RESULTS

On the basis of 511 sets of longitudinal observations, we established new reference percentiles of UV diameter, blood flow velocities, volume flow, and blood flow normalized for fetal weight and abdominal circumference. They reflected some of the developmental patterns of previous cross-sectional studies, but with important differences, particularly near term. The UV blood flow showed a continuous increase until term, whereas the flow normalized per unit fetal weight, a corresponding reduction. Calculating the blood flow on the basis of intensity-weighted mean velocity or 0.5 of the maximum velocity gave almost interchangeable results for most fetuses.

CONCLUSION

New reference ranges for UV blood flow based on longitudinal observations appear slightly different from cross-sectional studies, and should be more appropriate for serial evaluation of fetal circulation.

Prenatal diagnosis of ductus venosus agenesis and its association with cytogenetic/congenital anomalies

OBJECTIVES

We present an observational study of 12 cases of anomalies of the umbilical and portal vein systems associated with absence of the ductus venosus (DV) diagnosed over the past 5 years. The hemodynamic implications of each pattern of umbilico-portal system anomalies associated with absence of the DV have been investigated, as well as the frequency and types of associated anomalies and their embryological origin.

METHODS

In all cases ultrasound, color Doppler, and cytogenetic investigations were performed.

RESULTS

Four main patterns of abnormal venous circulation were documented: (1). the umbilical vein (UV) bypasses the liver and drains into the right atrium directly or through a dilated coronary sinus (three cases); (2). the UV bypasses the liver, with an infrahepatic or suprahepatic connection directly to the inferior vena cava (IVC) (two cases); (3). the UV bypasses the liver and drains directly into the iliac or renal veins (four cases); and (4). the UV drains directly into the portal veins (three cases). Among seven cases with other associated anomalies (58%), there were three cases of Turner's and Noonan's syndromes. Two fetuses and two neonates died and there were two terminations of pregnancy (TOP).

CONCLUSIONS

In utero diagnosis of ultrasound patterns associated with DV anomalies is feasible. Fetal karyotyping should be considered, serial ultrasound examinations recommended and, in the presence of heart failure, delivery can be anticipated.

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.

The anatomy of the umbilical, portal and hepatic venous systems in the human fetus at 14-19 weeks of gestation

BACKGROUND

Ultrasound imaging of the fetal ductus venosus is becoming increasingly commonplace in clinical practice. The true anatomical relationships of the fetal umbilical and portal venous systems have not been clearly defined due to paucity of published data on the relevant anatomy. This has led to confusing terminology when describing the fetal umbilical, portal and hepatic circulations. The aim of the present study was to examine and document the anatomy of the umbilical, portal and hepatic venous systems and to propose a standardized nomenclature.

METHODS

This was a prospective study on 11 fetuses obtained from medical termination of pregnancies between 14 and 19 weeks of gestation. The liver was microdissected to expose the branching pattern and anatomical relations of the umbilical, portal and hepatic venous systems.

RESULTS

A wide L-shaped venous confluence at the terminal end of the umbilical vein, termed the portal sinus, was identified. The portal sinus was connected to the right and left hepatic lobes, by the right and left intrahepatic portal veins, respectively. The extrahepatic portal vein drained into the portal sinus just before the origin of the right intrahepatic portal vein. The ductus venosus, a branchless straight vessel, originated from the portal sinus and ascended steeply in the direction of the diaphragm. Numerous small vessels draining the liver converged into three main hepatic veins, which open into the subdiaphragmatic vestibulum.

CONCLUSION

Based on detailed sequential anatomical dissection and clear illustrations, the present study documents the anatomy of the umbilical, portal and hepatic venous systems. Taking into account the embryological origin of the vessels, a new anatomically appropriate and simplified nomenclature of these venous systems is proposed. In clinical practice, the consistent use of the suggested terminology would allow collection of comparable data between units and enable operators to be confident of which vessels they are sampling by Doppler ultrasound.

Absence of the ductus venosus: report of 10 new cases and review of the literature

OBJECTIVE

To assess the clinical significance of the absence of the ductus venosus.

DESIGN

A retrospective study with a review of the literature.

METHODS

The archives of our ultrasound laboratory and the English literature were searched for cases with a prenatal diagnosis of absence of the fetal ductus venosus.

RESULTS

Between 1985 and 2000, 10 fetuses were diagnosed in our center as having absence of the ductus venosus. The review of the literature revealed 23 cases. Three main patterns of abnormal venous circulation were documented: (1) umbilical vein bypassing the liver and connecting directly to the right atrium (46%); (2) umbilical vein bypassing the liver and connecting to the inferior vena cava mostly through one of the iliac veins (25%); (3) umbilical vein connecting to the portal circulation without giving rise to the ductus venosus (21%). Major anomalies, including chromosomal aberrations, were found in 8/33 (24%) cases. Hydrops developed in 11/33 (33%) cases. Twenty fetuses with isolated absence of the ductus venosus were delivered, and 5 (20%) died. The portal vein was found to be absent in half of the infants examined after birth.

CONCLUSIONS

Our results and the review of literature suggest that absence of the ductus venosus is associated with a high incidence of fetal anomalies and adverse outcomes, including associated malformations, chromosomal aberrations, in utero heart failure and absence of the portal vein. Heart failure and absence of the portal vein seem particularly frequent when absence of the ductus venosus is associated with a connection of the umbilical vein to either the inferior vena cava or the right atrium.