Arterial blood flow velocity waveforms of the pelvis and lower extremities in normal and growth-retarded fetuses

Doppler Ultrasonography of the Fetal Tibial Artery in High-Risk Pregnancy and Its Value in Predicting and Monitoring Fetal Hypoxia in IUGR Fetuses

Background and Objectives: Intrauterine growth restriction (IUGR) is the term used to describe a fetus whose estimated weight is less than the 10th percentile of its age growth curve. IUGR is the second most common cause of perinatal death. In many cases there is a deficiency in the standardization of optimal management, prenatal follow-up and timing of delivery. Doppler examination is the most sensitive test that can assess the condition of the fetus and indicate fetal intrauterine hypoxia. Numerous studies of the fetal intrauterine state focus on the umbilical artery and the fetal cerebral blood vessels, while the peripheral arteries have so far received insufficient attention. Materials and Methods: We present a case of an IUGR fetus monitored with a non-stress test (NST) and a Doppler examination of the fetal arteries (tibial, umbilical, middle cerebral and uterine) and the ductus venosus. In this case the first early sign of fetal hypoxia was revealed by blood flow changes in the tibial artery. Results: We hypothesize that peripheral vascular changes (in the tibial artery) may more accurately reflect the onset of deterioration in the condition of the IUGR fetus, such that peripheral blood flow monitoring ought to be employed along with other techniques already in use. Conclusion: This paper describes the clinical presentation of an early detection of late IUGR hypoxia and claims that blood flow changes in the tibial artery signal the worsening of the fetus’s condition.

Size and shape of the four-chamber view of the fetal heart in fetuses with an estimated fetal weight less than the tenth centile

BACKGROUND

Fetuses with an estimated fetal weight below the 10^th centile have an increased risk of adverse perinatal and long-term outcomes as well as increased rates of cardiac dysfunction, which often alters cardiac size and shape of the 4-chamber view and the individual ventricles. As a result, a simple method has emerged to screen for potential cardiac dysfunction in fetuses with estimated fetal weights <10^th centile by measuring the size and shape of the 4-chamber view and the size of the ventricles.

OBJECTIVE

To determine the number of fetuses with an abnormal size and shape of the 4-chamber view and size of the ventricles in fetuses with an estimated fetal weight <10^th centile.

MATERIALS AND METHODS

This was a retrospective study of 50 fetuses between 25 and 37 weeks of gestation with an estimated fetal weight <10^th centile. Data from their last examination were analyzed. From an end-diastolic image of the 4-chamber view, the largest basal-apical length and transverse width were measured from their corresponding epicardial borders. This allowed the 4-chamber view area and global sphericity index (4-chamber view length/4-chamber view width) to be computed. In addition, tracing along the endocardial borders with speckle tracking software enabled measurements of the right and left ventricular chamber areas and the right ventricle/left ventricle area ratios to be computed. Doppler waveform pulsatility indices from the umbilical (umbilical artery pulsatility index) and middle cerebral arteries (middle cerebral artery pulsatility index) were analyzed, and the cerebroplacental ratio (middle cerebral artery pulsatility index/umbilical artery pulsatility index) computed. Umbilical artery pulsatility indices >90^th and cerebroplacental ratios <10^th centile were considered abnormal. Using data from the control fetuses, the centile for each of the cardiac measurements was categorized by whether it was <10^th or >90^th centile, depending upon the measurement.

RESULTS

Of the 50 fetuses with estimated fetal weight <10^th centile, 50% (n = 25) had a normal umbilical artery pulsatility index and cerebroplacental ratio. These fetuses had significantly more (P < 0.02 to <0.0001) abnormalities of the size and shape of the 4-chamber view than controls. In all, 44% had a 4-chamber view area >90^th centile, 32% had a 4-chamber view global sphericity index <10^th centile, 56% had a 4-chamber view width >90^th centile, and 80% had 1 or more abnormalities of size and/or shape. The remaining 50% of fetuses (n = 25) had abnormalities of 1 or both for the umbilical artery pulsatility index and/or cerebroplacental ratio. These fetuses had significantly higher rates of abnormalities (P <0.05 to <0.0001) than controls for the following 4-chamber view measurements: 36% had a 4-chamber view area >90^th centile; 28% had a 4-chamber view global sphericity index <10^th centile; and 68% had a 4-chamber view width >90^th centile. Only those fetuses with an abnormal umbilical artery pulsatility index had significant changes in ventricular size; 56% had a left ventricular area <10^th centile; 28% had a right ventricular area <10^th centile; 36% had right ventricular/left ventricular area ratio >90^th centile. One or more of the above abnormal measurements were present in 92% of the fetuses.

CONCLUSION

Higher rates of abnormalities of cardiac size and shape of the 4-chamber view were found in fetuses with an estimated fetal weight <10^th centile, regardless of their umbilical artery pulsatility index and cerebroplacental ratio measurements. Those with a normal umbilical artery pulsatility index and an abnormal cerebroplacental ratio had larger and wider measurements of the 4-chamber view. In addition, the shape of the 4-chamber view was more globular or round than in controls. These fetuses may have an increased risk of perinatal complications and childhood and/or adult cardiovascular disease. Screening tools derived from the 4-chamber view, acting as surrogates for ventricular dysfunction, may identify fetuses who could benefit from further comprehensive testing and future preventive interventions.

Physiological adaptation of the growth-restricted fetus

The growth-restricted fetus in utero is exposed to a hostile environment and suffers undernutrition and hypoxia. To cope with the stress, the fetus changes its physiological functions. These adaptive changes aid intrauterine survival; however, they can lead to permanent functional and structural changes that can contribute to the development of serious chronic diseases later in life. Epigenetic mechanisms are an important part of the pathophysiological processes behind this "developmental origin of adult diseases." The dominant cardiovascular adaptive change is the redistribution of blood flow in hypoxic fetuses, with preferential supply of blood to the fetal brain, myocardium, and adrenal glands. The proportion of blood from the umbilical vein to the ductus venosus and foramen ovale increases, which increases the cardiac output of the left heart ventricle. The increased perfusion of fetal brain can be followed with Doppler ultrasound as increased diastolic velocities and decreased pulsatility index in the middle cerebral artery.

Fetal dorsalis pedis artery velocimetry in the second and third trimesters

OBJECTIVES

This study aimed to establish reference ranges for Doppler parameters of the fetal dorsalis pedis artery and to compare them with those of the anterior tibial artery.

METHODS

Dorsalis pedis artery velocimetry was performed in 138 singleton fetuses. Intraobserver repeatability coefficients and differences between measurements of bilateral legs were also evaluated. Comparisons were made between the pulsatility index in the dorsalis pedis and anterior tibial arteries.

RESULTS

The average maximum velocity of the dorsalis pedis artery increased from approximately 12.2 cm/s at 18 weeks' gestation to 33.6 cm/s at 39 weeks' gestation, whereas the minimum velocity did not show any significant variation during the observed gestational weeks. The average pulsatility index increased from about 2.0 at 18 weeks' gestation to 3.1 at 39 weeks' gestation. The pulsatility index was lower in the dorsalis pedis artery than in the anterior tibial artery.

CONCLUSIONS

Doppler parameters of the dorsalis pedis artery can be easily and accurately acquired by trained examiners and therefore are potential means for evaluating related fetal vascular development. However, it is still unclear whether changes exist in fetuses with limb diseases, and further investigation is needed.

Bowel circulation in normally grown and growth-restricted fetuses

OBJECTIVES

The purpose of this study was to characterize bowel blood flow and its relationship with cerebral and placental circulations in normally grown and growth-restricted fetuses.

METHODS

In a cross-sectional prospective study of singleton normally grown fetuses, Doppler blood flow pulsatility indices were measured in the superior mesenteric artery, middle cerebral artery, and umbilical artery from 19 to 38 weeks' gestation. The same Doppler parameters were examined in intrauterine growth-restricted (IUGR) fetuses and analyzed as two groups: (1) without a brain-sparing effect, defined as an umbilical artery/middle cerebral artery ratio of less than 1; and (2) with a brain-sparing effect, defined as an umbilical artery/middle cerebral artery ratio of greater than 1.

RESULTS

A total of 262 appropriate-for-gestational-age fetuses were analyzed for superior mesenteric artery Doppler pulsatility index values; 196 were simultaneously examined for umbilical artery and middle cerebral artery pulsatility index values. Forty-three IUGR fetuses were similarly analyzed. In appropriate-for-gestational-age fetuses, both the bowel and brain circulations showed a globally higher pulsatility index as pregnancy advanced, resulting in an almost constant middle cerebral artery/superior mesenteric artery ratio (r(2) = 0.079). The IUGR fetuses had a lower superior mesenteric artery pulsatility index compared to the appropriate-for-gestational-age fetuses, which was more pronounced in those with brain sparing (group 2) than in group 1 (Z = -0.97 and -0.53, respectively; P < .0001). The middle cerebral artery/superior mesenteric artery ratio was higher with respect to the appropriate-for-gestational-age fetuses in group 1, whereas the ratio in group 2 was lower (Z = 0.16 and -0.60).

CONCLUSIONS

We have shown the existence of a superior mesenteric artery sparing effect in IUGR fetuses. This reaction seems to correlate positively with the severity of the growth restriction.

Fetal cardiovascular reflex responses to hypoxaemia

The fetus mounts a coordinated cardiovascular response to an insult of acute hypoxaemia which involves neural and endocrine components. During acute hypoxaemia in late pregnancy there is a transient bradycardia, a gradual increase in arterial blood pressure and an increase in heart rate variability. In addition, there is a redistribution of the combined ventricular output favouring the cerebral, myocardial and adrenal circulations by shunting blood away from the peripheral circulations. A component of the increase in peripheral vascular resistance and the increase in arterial blood pressure during acute hypoxaemia is mediated via increases in plasma concentrations of vasoconstrictor hormones such as vasopressin, angiotensin II and neuropeptide Y. Whilst an increase in plasma ACTH and cortisol is also seen during acute hypoxaemia, their contribution to cardiovascular control in fetal sheep is less clear.

Evidence has been presented to suggest that a number of these cardiovascular and endocrine responses to acute hypoxaemia are chemorefiex in nature, mediated principally by carotid chemoreceptor afferents. In addition, this reflex may be modifiable in terms of changes in magnitude and gain: first, by an influence of the intrauterine environment during chronic hypoxaemia and second, through genetic influences, in animals adapted to life at high altitude.

Diagnosis and management of intrauterine growth restriction

The growth-restricted fetus is a fetus who fails to reach his growth potential and is at risk for perinatal morbidity and mortality. When a fetus has an estimated weight below the 10th percentile, in the absence of congenital anomalies and in the presence of a normal amount of amniotic fluid, Doppler velocimetry gives the most important information to differentiate the truly growth-restricted fetus from the fetus that is constitutionally small but otherwise normal. One area of debate and research is whether Doppler velocimetry can help in timing the delivery of the growth-restricted fetus. Data appear to support the use of ductus venosus velocimetry in deciding when to deliver, but randomized data on this point are still lacking.

Lung fractional moving blood volume in normally grown and growth restricted foetuses

OBJECTIVE

To examine foetal lung blood perfusion using power Doppler ultrasound (PDU) and to compare fractional moving blood volume (FMBV) and mean pixel intensity (MPI) estimations in the lungs of normally grown (NG) foetuses and foetuses with intrauterine growth restriction (IUGR) and also to correlate foetal lung FMBV and MPI with respiratory complications after birth.

METHODS

Lungs of 47 NG and 25 IUGR foetuses after 32 weeks of gestation were examined with PDU. FMBV and MPI were estimated in a defined region in the posterior part of the foetal lung closest to maternal abdominal wall. FMBV and MPI were correlated to foetal weight deviation and gestational age. Perinatal outcome and respiratory complications after birth were recorded in both groups.

RESULTS

There were significantly lower FMBV and MPI values in IUGR than in NG foetuses. The overall variation was lower for FMBV than for MPI. There was a slightly higher correlation between FMBV and foetal weight deviation [r = 0.33, 95% confidence intervals (CI) 0.11-0.52] than between MPI and foetal weight deviation (r = 0.26, 95% CI 0.03-0.46). There was no significant correlation between FMBV or MPI and gestational age. No differences between the groups were found in the rate of respiratory complications, and they were not correlated either to the FMBV or MPI.

CONCLUSION

FMBV and MPI, estimated from the PDU signals of foetal lung circulation, showed lower values in third-trimester pregnancies complicated by IUGR. The frequency of neonatal respiratory complications was not increased in cases with low pulmonary FMBV and MPI values.

Fetal growth restriction due to placental disease

Normal fetal growth depends on the genetically predetermined growth potential and its modulation by the health of the fetus, placenta and the mother. Fetuses that are small because of intrauterine growth restriction (IUGR) are at higher risk for poor perinatal and long-term outcome than those who are appropriately grown. Of the many potential underlying processes that may result in IUGR, placental disease is clinically the most relevant. Fetal cardiovascular and behavioral responses to placental insufficiency and the metabolic status are interrelated. The concurrent evaluation of fetal biometry, amniotic fluid volume, heart rate patterns, arterial and venous Doppler, and biophysical variables therefore allow the most comprehensive fetal evaluation in IUGR. In the absence of successful intrauterine therapy, the timing of delivery is perhaps the most critical aspect of the antenatal management. A discussion of the fetal responses to placental insufficiency and a management protocol that accounts for multiple Doppler and biophysical parameters as well as gestational age is provided in this review.

Doppler blood flow in obstetrics

PURPOSE OF REVIEW

Our review on Doppler ultrasound in obstetrics aims to identify which vessels have a definite clinical role in obstetrics.

RECENT FINDINGS

The use of Doppler ultrasonography in the diagnosis and management of the intrauterine growth-restricted fetus improves the perinatal morbidity and mortality. However, the timing of delivery of the intrauterine growth-restricted fetus, based on Doppler ultrasonography, remains the subject of investigation. Robust data exist on the management of fetuses at risk for anemia because of red cell alloimmunization by using the middle cerebral artery peak systolic velocity. Appropriate training for the correct assessment of this vessel is fundamental. Doppler ultrasonography of the umbilical artery is useful in the counseling of patients with pregnancies complicated by twin-twin transfusion syndrome.

SUMMARY

Recently, Doppler ultrasonography has been shown to be helpful to the obstetricians in the diagnosis of the IUGR fetus, diagnosis of fetal anemia, twin-twin transfusion syndrome. These are the basis for timing the delivery of the IUGR fetus. However, more data are necessary. Doppler ultrasonography should be used to assess the fetal ductus arteriosus in patients treated with prostaglandin inhibitors. Doppler is also an important part of the fetal echocardiogram.

A transmission line model of the human foetal circulatory system

A transmission line model of the human foetal circulatory system is presented. The model has been developed in the frequency domain with the cardiac input modeled as a flow rather than as a pressure pulse and is structured upon electrical transmission line analogies. The model is formed by cascading solutions to the two-dimensional Navier-Stokes equations for both oscillatory and steady, laminar viscous fluid flow in isotropic visco-elastic tubes with thick walls, which are constrained by surrounding tissues. Simulations allow for representation of both forward and retrograde travelling flow and pressure waves in all of the main foetal arterial vessels. The solution is verified by a comparison of model generated Doppler indices in the thoracic aorta, abdominal aorta, iliac artery and both ends of the umbilical arteries with previously published indices obtained by clinical measurements in these arteries. For simulations of blood flow in a healthy foetus, the model generated Pulsatility and Resistance indices were on average within 8% of the corresponding clinical measurements. The model results also demonstrates that placental resistance must increase by a factor of three, corresponding to a 60% decrease in flow to the placenta, before umbilical arterial absent end diastolic flow is observed. Differences between indices obtained from simulations at opposite ends of the umbilical arteries increase with increasing placental resistance.

Doppler velocimetry in the adrenal artery in human fetuses

BACKGROUND

Fetal hypoxia and/or acidosis causes redistribution of blood flow to the high-priority organs including the adrenal glands. Although this phenomenon is well described in the human cerebral and placental circulations using Doppler velocimetry, there are few reports about the adrenal glands.

AIM

To clarify the gestational age-related changes in adrenal blood flow in normal fetuses and fetuses at risk of hemodynamic derangement.

MATERIAL AND METHODS

In 153 normal cases, the resistance indices (RIs) calculated from the blood flow velocity waveforms (FVWs) in the middle adrenal artery (MAA) were obtained from 24 weeks to construct nomogram using regression analysis. Twenty-seven complicated cases were divided according to the 5%ile RI values in the MAA, and clinical outcomes were retrospectively compared.

RESULT

The RI values in the MAA increased until 31 weeks and decreased thereafter. The 50%ile regression curve was represented as RI=-0.000914 (weeks)(2)+0.0579 weeks-0.181. Of the 27 complicated cases, 13 had RIs in the MAA below the 5%ile. Cases with low RI had significantly higher RI ratio in regard of UA/MCA; higher occurrence of abnormal FHR patterns on observation; higher incidence of cesarean delivery for nonreassuring fetal well-being status; earlier gestational age at delivery; lower birth weights and longer periods of admission to NICU than the cases with normal RI.

CONCLUSION

We have described the nomogram for the RI in the MAA. In conditions of fetal hypoxia or acidemia, blood flow redistribution to the adrenal glands may occur and the analysis of the adrenal artery FVWs may be useful in detection of fetal altered hemodynamics.

Pain and stress in the human fetus

Invasive diagnostic and therapeutic techniques are increasingly applied to the fetus. It is not known if the fetus feels pain during such procedures, but the fetus does mount significant stress hormonal and circulatory changes in response to these from 18-20 weeks. Perinatal stress may have long-term neurodevelopmental implications. During open fetal surgery, maternal general anaesthesia provides fetal anaesthesia. However, in closed procedures, fetal analgesia presents difficulties. The optimal drug, dose, and route of administration remain to be determined.

Comparison of alterations in fetal regional arterial vascular resistance in appropriate-for-gestational-age singleton, twin and triplet pregnancies

The objective of this longitudinal study was to evaluate alterations in fetal vascular resistance of fetal peripheral arteries with advancing gestation in singleton appropriate-for-gestational-age (S-AGA), twin appropriate-for-gestational-age (Tw-AGA) and triplet appropriate-for-gestational-age (Tri-AGA) infants. Colour Doppler flow imaging and pulsed Doppler ultrasonographic examinations were performed on 35 S-AGA, 52 Tw-AGA and 12 Tri-AGA fetuses. The pulsatility index for middle cerebral artery (MCAPI), umbilical artery (UAPI), descending aorta (DAPI), splenic artery (SAPI), renal artery (RAPI) and femoral artery (FAPI) was measured as vascular resistance every 2 weeks after 15 weeks of menstrual age until delivery. Optimal models and normal ranges for pulsatility index for each artery in each group were generated. The alterations in various fetal regional arterial pulsatility indices with advancing gestational age showed no significant differences in S-AGA, Tw-AGA and Tri-AGA infants, respectively. These results suggest that there is no significant difference for regional arterial vascular resistance in AGA fetuses among singleton, twin, and triplet pregnancies, whereas there was a slight difference in fetal growth pattern among singleton, twin, and triplet pregnancies described in our previous investigation.

Splenic artery velocity waveforms in small-for-gestational-age fetuses: relationship with pH and blood gases measured in umbilical blood at cordocentesis

OBJECTIVE

Our purpose was to relate velocity waveforms from the splenic artery with pH and blood gas levels measured at cordocentesis in small-for-gestational-age fetuses and to compare the diagnostic efficiency of splenic artery waveforms with that of other fetal arterial and venous vessels in predicting acid-base status.

STUDY DESIGN

Cross-sectional recordings from the splenic artery were obtained by color and pulsed Doppler techniques in 316 appropriately grown fetuses, 12 small-for-gestational-age fetuses with normal umbilical artery velocity waveforms (group 1), and 30 small-for-gestational-age fetuses with abnormal umbilical artery velocity waveforms (group 2). Measurements of splenic artery pulsatility index values in small-for-gestational-age fetuses were compared with those of appropriate-for-gestational-age fetuses. Associations of splenic artery pulsatility index with Po2, Pco2, and pH values measured at cordocentesis were examined and compared with those of umbilical artery, middle cerebral artery, and inferior vena cava.

RESULTS

In appropriately grown fetuses pulsatility index values from the splenic artery decrease with advancing gestation (r = 0.51, p < 0.0001). Splenic artery pulsatility index values are lower in group 2 (p < 0.001) but not in group 1 small-for-gestational-age fetuses (p = 0.211). The amplitude of the decrease in the pulsatility index is significantly associated with fetal hypoxemia (r = 0.646, p < 0.001), acidemia (r = 0.593, p < 0.001) and hypercapnia (r = 0.577, p < 0.001). However, logistic regression demonstrates that hypoxia is better predicted by middle cerebral artery pulsatility index, whereas hypercapnia and acidosis are more closely associated with the percent of reverse flow in inferior vena cava.

CONCLUSION

A decrease in the splenic artery pulsatility index occurs in small-for-gestational-age fetuses in the presence of abnormal pH and blood gas values, but a more accurate assessment of acid-base status may be obtained with the study of the middle cerebral artery and inferior vena cava.

Prenatal diagnosis of an extensive haemangioma of the fetal leg: a case report

Extensive haemangioma with platelet consumption (Kasabach-Merritt syndrome) is rare. The lesion is usually a single cutaneous cavernous haemangioma similar to that found in our patient. Multiple superficial strawberry naevi were also seen all over the rest of the body. This condition was diagnosed antenatally in this patient with the use of colour Doppler. There is one recent report where the thrombocytopaenia was diagnosed by cordocentesis. Unfortunately the baby developed heart failure with intractable coagulopathy and died 2 days later.

Common iliac artery flow velocity waveforms in fetuses with a single umbilical artery: a longitudinal study

OBJECTIVES

In fetuses with a single umbilical artery the entire blood flow to the placenta is transported through the common and internal iliac arteries from the side of the single artery, whereas the pelvic vessels from the side of the missing artery do not participate in the fetoplacental circulation. The aim of this study was to investigate the effect of gestational age on pelvic arterial blood flow in fetuses with single umbilical artery.

DESIGN

In 15 fetuses with a single umbilical artery (SUA), common iliac artery flow velocity waveforms were studied longitudinally using high resolution colour Doppler ultrasonography at three gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 37 weeks. The pulsatility index was measured in each common iliac artery and mixed model analysis of variance was used to examine the effect of gestational age and side.

RESULTS

There was a highly significant difference in pulsatility index between common iliac arteries at all gestational ages, the values always being higher on the side that did not participate in the fetoplacental circulation (P < 0.001). For increasing gestation, the pulsatility index fell significantly in the SUA side but remained high in the non-SUA side (P < 0.001).

CONCLUSIONS

This study shows that the asymmetry in the pelvic arterial blood flow in fetuses with SUA increases as pregnancy progresses, consistent with decreasing vascular resistance in the placenta and increasing resistance in the lower extremities.

Flow velocity waveforms of the ductus arteriosus in appropriate and small-for-gestational-age fetuses

OBJECTIVES

To assess ductus arteriosus velocity waveforms in the appropriate and small-for-gestational-age (SGA) fetuses.

STUDY DESIGN

Ductus arteriosus flow velocity waveforms were obtained in 14 normal fetuses in a longitudinal study and in 139 normal fetuses in a cross-sectional study with pulsed and continuous Doppler ultrasonography. Ductus velocity waveforms were also determined in 25 SGA fetuses whose gestational age ranged between 20 and 34 weeks (mean +/- SD: 30 +/- 4.1 weeks).

RESULTS

Mathematical modeling demonstrated that the peak systolic velocity, lowest diastolic velocity, and mean velocity of the ductus arteriosus increased with advancing gestation in both the longitudinal and cross-sectional study, but considerable individual variability was seen in the longitudinal study. The pulsatility index did not change significantly. The ductal parameters were in the normal range in all the SGA fetuses.

CONCLUSIONS

The blood velocity of the ductus arteriosus increase with advancing gestation. Our results suggest that Doppler ultrasonographic study of the fetal ductus arteriosus, unlike Doppler study of the umbilical artery or middle cerebral artery, is not useful as an indicator of adverse fetal outcome.

Doppler flow velocimetry of the splenic artery in the human fetus: is it a marker of chronic hypoxia?

OBJECTIVE

The aim of this investigation was to describe splenic artery flow velocity waveforms in the appropriate- and small-for-gestational-age human fetus.

STUDY DESIGN

Splenic artery flow velocity waveforms were prospectively obtained from 95 appropriate- and 15 small-for-gestational-age fetuses with pulsed Doppler ultrasonography. The resistance index was used to quantify the Doppler waveform.

RESULTS

A second-degree polynomial model expressed the changes of the resistance index in appropriate-for-gestational-age fetuses with advancing gestation (y = 0.057x [Weeks] - 0.001x2, r = 0.53, p < 0.001). In 14 of 15 (93%) small-for-gestational-age fetuses the splenic artery resistance index was below the mean for gestational age. In five of 15 (33%) small-for-gestational-age fetuses the resistance index of the splenic artery was < 2 SEMs. A trend toward a higher hematocrit was noted in the five fetuses with splenic artery resistance index values < 2 SEMs (50.2%) compared with other small-for-gestational-age fetuses (43.0%).

CONCLUSION

Our results suggest that some small-for-gestational-age fetuses have decreased resistance at the level of the splenic artery. We postulate that the increased erythropoietin level, stimulated by hypoxia, results in decreased resistance at the level of the splenic artery in small-for-gestational-age fetuses. Finally, management of the small-for-gestational-age fetus may be aided by the study of the splenic artery waveforms.

Discordant iliac and femoral artery flow velocity waveforms in fetuses with single umbilical artery

OBJECTIVE

The aim of this study was to investigate pelvic and femoral arterial flow velocity waveforms in fetuses with a single umbilical artery.

STUDY DESIGN

Seven fetuses with single umbilical artery and no other ultrasonographically detected anomalies were studied with color Doppler ultrasonography at a median gestational age of 24 weeks (range 18 to 34 weeks). Flow velocity waveforms from the relevant vessels were obtained as follows: (1) umbilical artery from a free loop of cord, (2) common iliac artery from both sides just below the aortic bifurcation, (3) internal iliac artery and intraabdominal portion of the umbilical artery from the vessel visualized alongside the fetal bladder, and (4) femoral artery on both sides from the upper third of the fetal thigh. The pulsatility index was measured, and comparisons were made with the paired t test. A p value < 0.05 was considered significant.

RESULTS

The pulsatility index in the umbilical artery was normal in all cases. There were highly significant differences between the common iliac arteries in each side (difference in pulsatility index 2.7, 95% confidence interval 2.0 to 3.5, p < 0.001). Significant differences between both femoral arteries were also noted (difference in pulsatility index 1.0, 95% confidence interval 0.3 to 1.7, p < 0.001). In both vessels the pulsatility index was always higher in the side that did not participate in the placental circuit.

CONCLUSION

This study demonstrates that fetuses with single umbilical artery have asymmetric arterial blood flow patterns in the pelvic and lower extremities.

Understanding the pathophysiology of intra-uterine growth retardation: the role of the 'lower limb reflex' in redistribution of blood flow

Doppler ultrasound was used to investigate the circulatory redistribution and underlying reflex responses of fetal cardiovascular compensation in 30 small-for-gestational age (SGA) fetuses. The utero-placental bed, umbilical artery and vein, thoracic and abdominal aorta, internal and external cerebral arteries were evaluated. The values were compared to reference ranges constructed from 135 normal pregnancies, correlated to fetal blood gases obtained by cordocentesis and compared to the outcomes. In Group I (mortality and morbidity), all fetuses had loss of end-diastolic frequencies (L-EDF) in the abdominal aorta (100%), but only 20 (87%) and 13 (56%) had L-EDF in the thoracic aorta and umbilical artery respectively. High vascular resistance in the placental bed and low impedance in the middle cerebral and common carotid arteries was found in 14 (61%), 12 (52%) and 20 (87%) fetuses, respectively. In Group II (Healthy infants) two fetuses had high utero-placental vascular resistance and one had brain-sparing. Doppler indices did not always reflect fetal hypoxaemia demonstrating that redistribution in SGA fetuses may not be triggered by a fall in pO2, and that hypoxaemia is an associated pathology but may not be the underlying cause. It is postulated that redistribution in SGA fetuses is regulated by reflex mechanisms (the 'lower limb reflex') which result in severe vasoconstriction in the abdominal aorta, mesentery and carcass, favouring the brain and cardiac muscles. This mechanism explains the good predictive value of L-EDF in the abdominal aorta for poor neonatal outcome (sensitivity, specificity and positive predictive value, all 100%).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of Doppler technology in the evaluation of fetal hypoxia

Failing intrauterine support to the fetus can lead to intrauterine growth retardation (IUGR) and hypoxia and it is associated with a high risk of perinatal morbidity and mortality. The main effects of moderate to severe hypoxia on the fetus are different degrees of blood flow redistribution and reduction of oxygen consumption to maintain oxygen delivery to the central organs at the expenses of peripheral organs. The redistribution results in a 'brain sparing' effect. Recently, a Doppler ultrasonic technology (continuous wave, pulsed wave and colour flow imaging) has been developed for the non invasive measurement of flow. Doppler velocimetry detects the flow velocity waveform (FVW) which reflects the cardiac output, the vascular compliance and the resistance to the flow in a defined point of the vessel. Velocity waveform indices or even simpler criteria, such as the presence or absence of diastolic flow or flow reverse during diastole, have been applied to a number of fetal vessels. A significant relationship exists between blood oxygen, systemic lactic acidosis (determined by cordocentesis) and increase PI values in umbilical artery (UA), thoracic aorta (TA) and renal artery (RA). Moreover, in experimental animals during steady state hypoxia, several cardiovascular parameters are affected (heart rate/cardiac output decreases and blood pressure increases) while placental flow don't show a significant variation thus suggesting a raise in placental vascular resistance. Redistribution of the flow may be reliably evaluated by the cerebroplacental ratio (i.e. ratio between PI of MCA and PI of UA, c/p).(ABSTRACT TRUNCATED AT 250 WORDS)

Middle cerebral artery flow velocity waveforms in normal and small-for-gestational-age fetuses

The middle cerebral artery flow velocity waveforms were obtained in 16 normal fetuses in a longitudinal study and in 128 normal fetuses in a cross-sectional study with pulsed Doppler ultrasonography. The pulsatility index values of the middle cerebral artery were higher at 25 to 30 weeks' gestation than those observed during the two periods of major cerebral cellular multiplication in the human fetus. In 9 of the 16 fetuses studied longitudinally we compared the pulsatility index values obtained at the end of gestation with those obtained at 1 month after delivery; no significant difference was observed. The pulsatility index of the middle cerebral artery was also determined in 33 small-for-gestational-age fetuses. A middle cerebral artery pulsatility index value below our normal range was recorded in 9 of the 33 small-for-gestational-age fetuses (27.3%). These small-for-gestational-age fetuses with abnormal pulsatility index values had a significantly higher incidence of abnormal fetal heart rate and admission into the neonatal intensive care unit. There were three deaths in the nine small-for-gestational-age fetuses with abnormal pulsatility index values (33.3%) and three deaths in the 24 small-for-gestational-age fetuses with normal pulsatility index values (12.5%). Our data indicate that the pulsatility index of the middle cerebral artery in the normal human fetus has a parabolic pattern during pregnancy and does not change significantly after delivery. The results suggest that the small-for-gestational-age fetus with a normal middle cerebral artery pulsatility index is at lower risk than the fetus with abnormal pulsatility index values; moreover, management of the small-for-gestational-age fetus may be aided by the study of the middle cerebral artery waveforms.