The clinical significance of absent or reverse end-diastolic flow in the fetal aorta and umbilical artery

Reduced fetal cerebral blood flow predicts perinatal mortality in a mouse model of prenatal alcohol and cannabinoid exposure

BACKGROUND

Children exposed prenatally to alcohol or cannabinoids individually can exhibit growth deficits and increased risk for adverse birth outcomes. However, these drugs are often co-consumed and their combined effects on early brain development are virtually unknown. The blood vessels of the fetal brain emerge and mature during the neurogenic period to support nutritional needs of the rapidly growing brain, and teratogenic exposure during this gestational window may therefore impair fetal cerebrovascular development.

STUDY DESIGN

To determine whether prenatal polysubstance exposure confers additional risk for impaired fetal-directed blood flow, we performed high resolution in vivo ultrasound imaging in C57Bl/6J pregnant mice. After pregnancy confirmation, dams were randomly assigned to one of four groups: drug-free control, alcohol-exposed, cannabinoid-exposed or alcohol-and-cannabinoid-exposed. Drug exposure occurred daily between Gestational Days 12-15, equivalent to the transition between the first and second trimesters in humans. Dams first received an intraperitoneal injection of either cannabinoid agonist CP-55,940 (750 µg/kg) or volume-equivalent vehicle. Then, dams were placed in vapor chambers for 30 min of inhalation of either ethanol or room air. Dams underwent ultrasound imaging on three days of pregnancy: Gestational Day 11 (pre-exposure), Gestational Day 13.5 (peri-exposure) and Gestational Day 16 (post-exposure).

RESULTS

All drug exposures decreased fetal cranial blood flow 24-hours after the final exposure episode, though combined alcohol and cannabinoid co-exposure reduced internal carotid artery blood flow relative to all other exposures. Umbilical artery metrics were not affected by drug exposure, indicating a specific vulnerability of fetal cranial circulation. Cannabinoid exposure significantly reduced cerebroplacental ratios, mirroring prior findings in cannabis-exposed human fetuses. Post-exposure cerebroplacental ratios significantly predicted subsequent perinatal mortality (p = 0.019, area under the curve, 0.772; sensitivity, 81%; specificity, 85.70%) and retroactively diagnosed prior drug exposure (p = 0.005; AUC, 0.861; sensitivity, 86.40%; specificity, 66.7%).

CONCLUSIONS

Fetal cerebrovasculature is significantly impaired by exposure to alcohol or cannabinoids, and co-exposure confers additional risk for adverse birth outcomes. Considering the rising potency and global availability of cannabis products, there is an imperative for research to explore translational models of prenatal drug exposure, including polysubstance models, to inform appropriate strategies for treatment and care in pregnancies affected by drug exposure.

Maternal Blood Fatty Acid Levels in Small and Adequate for Gestational Age Pregnancies

Background

The aim is to assess the levels of fatty acids (FAs) in pregnancies with small for gestational age (SGA) and adequate for gestational age (AGA) fetuses, constituting an association between FAs and fetal growth; according to the role of FA, lower levels were expected in SGA.

Materials and Methods

This was an analytical cross-sectional study including pregnant women with gestational ages of 26-36 weeks with AGA and constitutionally SGA fetuses diagnosed by ultrasonography. The levels of saturated, trans, monounsaturated, and polyunsaturated fatty acids were measured using centrifugation and liquid chromatography. Student's t test and general linear model using gestational age as covariant were used to compare the levels of FAs and the groups (AGA and SGA). Chi-square was used to evaluate the association between groups and studied variables. Pearson correlation coefficient and linear regression were used to evaluate the correlation between the levels of FAs and gestational age.

Results

Peripheral blood was collected from 67 pregnant women, 3 of whom were excluded from the study. No significant statistical differences were observed between SGA (n = 40) and AGA (n = 24) in relation to saturated, trans, monounsaturated, and polyunsaturated fatty acids (p > 0.05). There was not significant correlation between saturated, trans, monounsaturated, and polyunsaturated FAs and gestational age (p > 0.05).

Conclusion

The levels of saturated, trans, monounsaturated, and polyunsaturated FAs were similar in constitutionally SGA and AGA fetuses.

Ursodeoxycholic acid inhibits uptake and vasoconstrictor effects of taurocholate in human placenta

Intrahepatic cholestasis of pregnancy (ICP) causes increased transfer of maternal bile acids to the fetus and an increased incidence of sudden fetal death. Treatment includes ursodeoxycholic acid (UDCA), but it is not clear if UDCA protects the fetus. This study explores the placental transport of the bile acid taurocholate (TC) by the organic anion-transporting polypeptide, (OATP)4A1, its effects on the placental proteome and vascular function, and how these are modified by UDCA. Various methodological approaches including placental villous fragments and Xenopus laevis oocytes were used to investigate UDCA transport. Placental perfusions and myography investigated the effect of TC on vasculature. The effects of acute TC exposure on placental tissue were investigated using quantitative proteomics. UDCA inhibited OATP4A1 activity in placental villous fragments and oocytes. TC induced vasoconstriction in placental and rat vasculature, which was attenuated by UDCA. Quantitative proteomic analysis of villous fragments showed direct effects of TC on multiple placental pathways, including oxidative stress and autophagy. The effects of TC on the placental proteome and vasculature demonstrate how bile acids may cause fetal distress in ICP. UDCA inhibition of OATP4A1 suggests it will protect the mother and fetus against the vascular effects of TC by inhibiting its cellular uptake. UDCA may protect the fetus in ICP by inhibiting OATP4A1-mediated bile acid transfer and TC-induced placental vasoconstriction. Understanding the physiologic mechanisms of UDCA may allow better therapeutic interventions to be designed specifically for the fetus in the future.-Lofthouse, E. M., Torrens, C., Manousopoulou, A., Nahar, M., Cleal, J. K., O'Kelly, I. M., Sengers, B. G., Garbis, S. D., Lewis, R. M. Ursodeoxycholic acid inhibits uptake and vasoconstrictor effects of taurocholate in human placenta.

Feeding issues in IUGR preterm infants

Intra-uterine growth restriction (IUGR) is a severe and quite common problem in obstetrics. A condition of placental dysfunction can lead to a cardiovascular adaptation in the fetus characterized by a redistribution of cardiac output to maintain oxygen supply to the heart, adrenal glands and brain - the so-called brain sparing effect - at the expense of visceral organs (such as the gastrointestinal system). This condition may predispose IUGR infants to impaired gut function after birth. A higher incidence of necrotizing enterocolitis (NEC) is documented in IUGR preterm infants. Therefore, a common practice in neonatal intensive care units is to delay feeds to reduce the risk of feeding intolerance. Recent trials, however, have shown that early enteral feeding in IUGR infants is safe and it would appear, on the basis of the few available data, that breast milk could offer protection against NEC. This mini-review offers an update on feeding in IUGR infants. Future perspectives on the usefulness of Doppler and regional splanchnic and cerebral saturation monitoring for deciding when to start feeding are also provided.

The role of Doppler and placental screening

Placental-associated diseases account for most cases of adverse perinatal outcome in developing countries. Uterine Doppler evaluation predicts most instances of early-onset preeclampsia and intrauterine growth restriction, but there is no evidence in favour of any prophylactic strategy in cases of an abnormal screening result. Umbilical artery Doppler investigation allows identifying those small-for-gestational-age foetuses at higher risk, and its use in these pregnancies improves a number of perinatal outcomes. Middle cerebral artery Doppler investigation reflects brain redistribution, and its use in combination with the umbilical artery in a cerebroplacental ratio seems to improve prediction of adverse outcome, mainly in near-term pregnancies, where most instances of adverse outcome occur in foetuses with normal umbilical artery. Ductus venosus Doppler waveform is a surrogate parameter of the foetal acid-base status. However, the benefits of its use in the management of early-onset growth restriction needs further evidence.

Intrauterine restriction (IUGR)

Perinatal mortality and morbidity is markedly increased in intrauterine growth restricted (IUGR) fetuses. Prenatal identification of IUGR is the first step in clinical management. For that purpose a uniform definition and criteria are required. The etiology of IUGR is multifactorial and whenever possible it should be assessed. When the cause is of placental origin, it is possible to identify the affected fetuses. The major complication is chronic fetal hypoxemia. By monitoring the changes of fetal vital functions it is thus possible to improve both management and outcome. The timing of delivery is crucial but the optimal management scheme has not yet been identified. When IUGR is identified at very early gestational ages, serial assessments of the risk of continuing the in utero fetal life under adverse conditions versus the risks of the prematurity should be performed. Delivery of IUGR fetuses should take place in centers where appropriate neonatal assistance can be provided. Careful monitoring of the IUGR fetus during labor is crucial as the IUGR fetus can quickly decompensate once uterine contractions have started.

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.

Computerized cardiotocography in the management of intrauterine growth restriction associated with Doppler velocimetry alterations

OBJECTIVE

To verify the reliability of computerized cardiotocography (cCTG) in the prediction of the oxygen metabolism status of fetuses with growth restriction and Doppler velocimetry alterations.

METHODS

From 24 third-trimester cesarean section performed because of intrauterine growth restriction (IUGR) and Doppler velocimetry alterations, there were 11 cases of fetal heart rate alterations (Dawes-Redman criteria were not satisfied) and 13 cases of reactive cCTG. Fetal lung maturity was detected by amniocentesis and blood samples for umbilical blood gas analysis (UBGA) were collected before the first neonatal breath from the umbilical artery in a double-clamped segment of the cord.

RESULTS

Umbilical cord gas analysis showed arterial cord blood pH to be 7.20 or less in 11 newborns (45.8%), 7.10 or less in 6 (25%), and 7.00 or less in 3 (12.5%). Linear regression analysis showed short-term variation (STV) in the fetal heart rate to be significantly correlated with umbilical artery pH (r = 0.49; P = 0.01) and pCO2 (r = -0.50; P = 0.01). There were no significant correlations between cCTG and the other UBGA parameters considered. Receiver operator curves permitted to calculate the STV values at which pathological neonatal UBGA values can be expected (pH < 7.00 and pCO2 > 80 mmHg). A short-term variation less than 4.5 ms was found to predict acidemia with a sensitivity of 100% and a specificity of 70% (positive predictive value, 33%; negative predictive value, 100%), and hypercarbia with a sensitivity of 100% and a specificity of 77.8% (positive predictive value, 55.6%; negative predictive value, 100%).

CONCLUSION

In view of the results of this study, 4.5 ms for STV may be a threshold below which timing of delivery should be decided in cases of fetal growth restriction.

Monitoring the IUGR fetus

Monitoring of the intrauterine growth retarded fetus in order to improve fetal outcome and define precisely the timing of delivery, when necessary, is based on the study of changes in vital functions observable in cases of hypoxemia. It is easy to believe that ultrasound equipment with Doppler facilities is present in the majority if not in all gynecological units. Cardiotocography is also widely used and the addition of a computerized evaluation system is not expensive and therefore should be available when facing high risk pregnancies such as intrauterine growth retarded cases. IUGR can be recognized through the use of ultrasound fetal biometry and clinical examination of maternal conditions in order to assess fetal conditions. If the above technologies are available further action, such as fetal Doppler study of fetal vessels and cardiotocography, can then be undertaken. In this paper, we will be discussing the issue of monitoring the fetus for fetal well-being, particularly in cases of intrauterine growth retarded fetuses.

Arterial and ductus venosus Doppler in fetuses with absent or reverse end-diastolic flow in the umbilical artery: longitudinal analysis

OBJECTIVE

To evaluate alterations of arterial and ductus venosus blood flow velocities during deterioration and their interdependence.

METHODS

37 high-risk pregnancies complicated by umbilical absent or reverse end-diastolic flow velocities (AREDV) were monitored by measurement of the pulsatility index of the umbilical artery, middle cerebral artery and ductus venosus waveforms.

RESULTS

The mean observation period was 16.5 days. There was a significant change in the pulsatility of waveforms in all vessels over the observation period. Compared with the ductus venosus, pulsatility of waveforms in the middle cerebral artery diverged from the normal range 2.2 weeks earlier. Increase in pulsatility in the umbilical artery was concomitant with venous but not with cerebral flow alterations. In addition, there was a correlation between the increase of venous but not arterial pulsatility and perinatal acidemia. Variability of pulsatility index values of the umbilical artery and the ductus venosus but not of the middle cerebral artery increased towards delivery.

CONCLUSIONS

Ductus venosus Doppler allows detection of further deterioration in centralized fetuses with umbilical AREDV. However, striking short-term variability has to be taken into account when considering this parameter.

Cyclic changes in the umbilical arterial flow in mono-chorionic, di-amniotic twin pregnancy

OBJECTIVE

To determine the effect of arterio-arterial anastomosis on the umbilical arterial flow in mono-chorionic, di-amniotic twin pregnancy.

SUBJECTS

Thirty-three women with mono-chorionic, di-amniotic twin pregnancy.

METHODS

Pulsed Doppler ultrasonographic examination was performed every 4 weeks to obtain umbilical arterial flow velocity waveforms in both two fetuses.

RESULTS

In five of the women, cyclic flow changes in the umbilical arterial flow were detected in the smaller fetus. All of these twins had arterio-arterial anastomosis on the surface of the placenta.

CONCLUSION

The fetuses in mono-chorionic and di-amniotic twin gestation who showed cyclic changes in umbilical arterial flow had arterio-arterial anastomosis. But, this characteristic flow was not observed every time.

Can the degree of retrograde diastolic flow in abnormal umbilical artery flow velocity waveforms predict pregnancy outcome?

OBJECTIVE

Reverse end-diastolic flow is the most pathological type of the umbilical artery flow velocity waveform. We aimed to investigate whether additional prognostic information can be obtained from umbilical artery waveforms in cases with reverse end-diastolic flow.

SUBJECTS AND METHODS

Umbilical artery Doppler velocity waveforms from 44 fetuses with reverse end-diastolic flow were analyzed and the following parameters measured: the highest amplitude and the area below the maximum velocity curve of forward and reverse flow (A, B and C, D, respectively) and the duration of forward and reverse flow (Tc and Td, respectively). Ratios A/B, C/D and Tc/Td were calculated. The cut-off values for A/B, C/D and Tc/Td with the best predictive values for perinatal death were established with the help of receiver operating characteristics curves. The three curves were compared with each other.

RESULTS

Of the three ratios, A/B and C/D had the best capacity to predict perinatal death. Both ratios had acceptable sensitivities, specificities and positive predictive values. In this regard, A/B and C/D were comparable. The cut-off values for A/B and C/D were 4.3 and 4.52, respectively. Survivors had I significantly higher A/B and C/D ratios than non-survivors (P = 0.0001 and 0.0003, respectively). Significantly more fetuses with A/B or C/D below the established cut-off values had pulsations in the venous system (P < 0.05). In fetuses with a gestational age < =210 gestational days the survival rate was significantly higher in those with A/B or C/D above the cut-off values (P = 0.03 and 0.003, respectively).

CONCLUSIONS

The A/B or C/D ratio can be used for quantification of the reverse end-diastolic flow waveforms in the umbilical artery and may offer additional information to the evaluation of fetal condition.

Antepartal assessment of IUGR fetuses

Intrauterine growth restriction (IUGR) should be defined on the basis of a prenatally recognized defective growth compared to that expected for this fetus. This condition is encountered in 10-15% of the pregnancies and the perinatal outcome is impaired mainly as a consequence of fetal hypoxemia that is present in 30% of IUGR fetuses. In order to allow for proper management, the IUGR should be recognized prenatally and the method of choice for this purpose is ultrasound fetal biometry. After the identification of IUGR, 2nd level tests should be performed in order to assess the fetal oxygenation conditions. The validity of Doppler investigation on fetal and umbilical vessels is discussed, and the importance of using computer assisted cardiotocography instead of traditional eye ball evaluation of the non-stress test is emphasized.

Fetal ultrasound

Ultrasound provides an opportunity to visualize the fetus and to assess its response to the intrauterine environment. The topic of fetal ultrasound is broad, and whole textbooks have been devoted to areas such as the diagnosis of anomalies. In an effort to provide current practical information, I have focused on the most common clinical questions asked when pregnant women are referred for obstetric ultrasound. We review the diagnoses of oligohydramnios, polyhydramnios, intrauterine growth retardation (IUGR), macrosomia, multiple pregnancy, and common fetal anomalies. Noninvasive assessment of fetal well-being is addressed, along with the use of sonography to refine risk assessment in patients with abnormal antenatal screening tests.

Comparison of umbilical-artery velocimetry and cardiotocography for surveillance of small-for-gestational-age fetuses

Intrauterine growth retardation is associated with an increased risk of fetal asphyxia as well as greater perinatal morbidity and mortality. Ultrasound fetometry enables detection of fetuses that are small for gestational age. Doppler velocimetry of the umbilical artery has good predictive ability for fetal distress, but it is not yet clear whether it could replace cardiotocography in antenatal surveillance of small-for-gestational-age fetuses. We have done a randomised comparison of the two methods. At four obstetric departments in Sweden, women with fetuses found to be small on ultrasound examination at 31 completed weeks of pregnancy or later were randomly assigned to antenatal surveillance with either doppler velocimetry (doppler; 214) or cardiotocography (CTG; 212). Pregnancies in the doppler group were managed according to a protocol based on blood-flow classes deriving from the semiquantitative evaluation of umbilical-artery velocity waveforms; unless the pregnancy was complicated by any other disorder, no antenatal cardiotocography was done. By comparison with the CTG group, the doppler group had fewer monitoring occasions (mean 4.1 [SD 3.1] vs 8.2 [6.2], p < 0.01), antenatal hospital admissions (68 [31.3%] vs 97 [45.8%], p < 0.01), inductions of labour (22 [10.3%] vs 46 [21.7%], p < 0.01), emergency caesarean sections for fetal distress (11 [5.1] vs 30 [14.2%], p < 0.01), and admissions to neonatal intensive care (76 [35.5%] vs 92 [43.4%], p = 0.10). The groups did not differ in gestational age at birth, birthweight, Apgar scores, or total number of caesarean deliveries. Umbilical-artery doppler velocimetry of small-for-gestational-age fetuses allows antenatal monitoring and obstetric interventions to be aimed more precisely than does cardiotocography.

The effect of improvement of umbilical artery absent end-diastolic velocity on perinatal outcome

OBJECTIVES

The purpose of this study was to analyze cases in which antenatal improvement of absent fetal umbilical artery end-diastolic velocity was detected and to correlate improvement with perinatal outcome.

STUDY DESIGN

Forty cases of umbilical artery absent end-diastolic velocity in singleton pregnancies were retrospectively reviewed. Maternal characteristics and perinatal outcomes were compared in cases where improvement of end-diastolic velocity was diagnosed and those in which no improvement was detected.

RESULTS

Eleven cases of absent end-diastolic velocity showed antenatal improvement and were associated with more advanced gestational age at delivery, longer diagnosis-to-delivery interval, larger birth weights, and a lower incidence of neonatal death than those fetuses without antenatal improvement.

CONCLUSION

Improvement of umbilical artery absent end-diastolic velocity can occur and is associated with improved pregnancy outcome when compared with patients without antenatal improvement of diastolic velocity.