Fetal cerebral and renal Doppler in small for gestational age fetuses in hypertensive pregnancies

Three-dimensional power Doppler analysis of cerebral circulation in normal and growth-restricted fetuses

The objective of the present study was to evaluate fetal cerebral circulation by using three-dimensional (3D) power Doppler ultrasound in normal and growth-restricted fetuses. A total of 100 normal grown fetuses were compared with other 25 with growth restriction (FGR). Three-dimensional power Doppler ultrasound was used to assess fetal cerebral 3D vascular indices: vascularization index, flow index (FI), and vascularization flow index (VFI). Both FI and VFI correlated positively with gestational age. On average, all the 3D vascular indices were increased in fetuses with FGR. The proportion of fetuses detected as having hemodynamic redistribution was higher when using 3D power Doppler indices than by means of the middle cerebral artery pulsatility index (52% versus 20%, P=0.002). In conclusion, two of the three indices increased during gestation. All the fetal cerebral 3D vascular indices are increased in fetuses with FGR. In these fetuses, there were more cases suggesting hemodynamic redistribution than expected by conventional Doppler studies.

Morphological and functional evaluation of normal and abnormal fetal growth by ultrasonography

Correction or estimation of gestational age is essential for the evaluation of fetal growth. When necessary, an appropriate fetal biometric parameter should be selected depending on fetal size. In the first trimester, crown-rump length (CRL) is appropriate, especially when the CRL is 20-40 mm. In the second trimester, biparietal diameter (BPD), head circumference (HC), and femur length (FL) are of equal predictability. Fetal weight estimation is still the basis of evaluation of fetal growth. The most predictable formula currently available includes the parameters BPD (or HC), abdominal circumference (AC), and FL. Serial measurements of AC are useful for diagnosis of intrauterine growth restriction (IUGR) and macrosomia. Quantitative evaluation of soft tissue deposition may be informative for macrosomia. Functional evaluation using Doppler velocimetry is essential in IUGR cases associated with uteroplacental insufficiency. Analysis of blood velocity waveforms of the umbilical and intracranial arteries, predominantly the middle cerebral artery, is widely performed. An increase in the pulsatility index (PI) or resistance index (RI) of the umbilical artery and/or a decrease in the PI or RI of the middle cerebral artery are highly predictable for fetal hypoxia and/or acidosis.

Fetal cerebrovascular response to chronic hypoxia—implications for the prevention of brain damage

Fetal hypoxia is one of the leading causes of perinatal morbidity and mortality. One of the most severe sequels of fetal hypoxic insult is the development of perinatal brain lesions resulting in a spectrum of neurological disabilities, from minor cerebral disorders to cerebral palsy. One of the most important fetal adaptive responses to hypoxia is redistribution of blood flow towards the fetal brain, known as the 'brain sparing effect'. The fetal blood flow redistribution in favor of the fetal brain can be detected and quantified by the Doppler cerebral/umbilical ratio (C/U ratio = cerebral resistance index (CRI)/umbilical resistance index (URI)). Our studies on animal models and human fetuses have demonstrated clearly that this phenomenon cannot prevent the development of perinatal brain lesions in the case of severe or prolonged hypoxia. Fetal deterioration in chronic and severe hypoxia is characterized by the disappearance of the physiological cerebral vascular variability (vasoconstriction and vasodilatation), followed by an increase in cerebral vascular resistance. However, our latest study on growth-restricted and hypoxic human fetuses has shown that perinatal brain lesions can develop even before the loss of cerebrovascular variability. The fetal exposure to hypoxia can be quantified by using a new vascular score, the hypoxia index. This parameter, which takes into account the degree as well as duration of fetal hypoxia, can be calculated by summing the daily % C/U ratio reduction from the cut-off value 1 over the period of observation. According to our results, the use of this parameter, which calculates the cumulative, relative oxygen deficit, could allow for the first time the sensitive and reliable prediction and even prevention of adverse neurological outcome in pregnancies complicated by fetal hypoxia.

Fetal Doppler Hypoxic index for the prediction of abnormal fetal heart rate at delivery in chronic fetal distress

OBJECTIVE

To design a Doppler Hypoxic index (HI), which takes into account both the duration and the intensity of fetal flow redistribution (i.e. hypoxia) for predicting the occurrence of abnormal fetal heart rate (FHR) at delivery.

METHOD

Sixty-six pregnancies with hypertension and/or growth retardation (IUGR) were investigated (age: 23+/-5 years; primigravidas: 30%, CS 59%; hospitalisation: 10+/-8 days, IUGR (<10 c) 82%, intensive care 23%, fetal death 1). Umbilical (URI) and cerebral (CRI) Doppler resistance indices, and the C/U ratio (CRI/URI) were measured every 2 days from admission to delivery. HI was calculated by summing the daily %C/U reduction (in % from normal cut-off limit 1.1) over the period of observation (or mean C/U reduction in % from 1.1 x number of days of observation). Doppler C/U and HI were compared with fetal heart rate (FHR) traces, and perinatal data.

RESULTS

HI > 160% was associated with abnormal FHR in 80% of the cases (PPV = 87%, NPV = 88%). HI > 160% predicted the occurrence of abnormal FHR 8+/-6 days before they happened.

CONCLUSION

A combination of intensity and duration of the fetal flow redistribution (i.e. hypoxia) evaluated by Doppler is correlated with the occurrence of abnormal fetal heart rate.

Acute reversible placental dysfunction and abnormal fetal heart rate at delivery

Acute placental dysfunction induced by malaria is characterized by umbilical artery resistance increase and cerebral artery resistance decrease during the crisis. The objective was to evaluate the sensitivity and specificity of fetal Doppler indices and crisis duration for predicting abnormal fetal heart rate (aFHR) at delivery several weeks after the crisis.

METHOD

Every day during the crisis, the umbilical and cerebral resistance indices were measured by Doppler. These indices allowed evaluation of the amplitude of the fetal flow redistribution (C/U = cerebral resistance/umbilical resistance ratio), the duration of the flow redistribution period (i.e. crisis duration) and the Hypoxic index (HI) (mean %C/U change x crisis duration).

RESULTS

POPULATION

46 pregnancies. Mean duration of the flow redistribution period 8+/-3.2 days, mean C/U change -9%+/-6; Hypoxic index -86+/-75; prematures 48%; aFHR 30%). Hypoxic index >150 predicted occurrence of aFHR with high sensitivity and specificity (83%/88%). The presence of abnormal flow distribution (C/U<1.1) and the duration of the period with flow disturbance (>8 days) predicted aFHR at delivery with a sensitivity of 45 and 48% and a specificity of 82 and 84%.

CONCLUSION

The Hypoxic index was more predictive of aFHR at delivery than the amplitude or the duration of the fetal flow redistribution triggered by placental insufficiency.

Fetal flow redistribution to the brain in response to malaria infection: does protection of the fetus against malaria develop over time?

OBJECTIVE

Malaria during pregnancy induces deterioration of placental function, resulting in transient fetal hypoxia. Our objective was to evaluate the sensitivity and specificity of fetal Doppler indices for prediction of abnormal fetal heart rate at delivery and to compare the amplitude of the fetal vascular response to malaria in 2 groups of fetuses (1994 and 1996) separated by an interval of 2 years.

METHODS

Every day during the crisis, the umbilical and cerebral resistance indices, the cerebral-umbilical resistance ratio, and the hypoxic index (mean percent cerebral-umbilical resistance ratio change x crisis duration) were calculated.

RESULTS

In group 2 (1996), the duration of the flow redistribution period was about 7 days (mean cerebral-umbilical resistance ratio change +/- SD, 7%+/-4%; hypoxic index, 49+/-26; premature, 35%; and abnormal fetal heart rate, 17.5%). A hypoxic index greater than 150 predicted abnormal fetal heart rate with high sensitivity and specificity (group 1, 80% and 85%; and group 2, 100% and 91 %). Moreover, in group 2 (1996), the amplitude of the fetal vascular response and the rate of long-duration crisis were significantly lower than in group 1 (1994; P < .01). Nevertheless, the hypoxic index was much more predictive of fetal heart rate at delivery than the amplitude or duration (i.e., crisis duration) of the flow redistribution.

CONCLUSIONS

The hypoxic index value during the crisis allowed prediction of abnormal fetal heart rate at delivery. In group 2, the absence of a long-term flow redistribution period and the smaller hemodynamic changes (lower hypoxic index) associated with a lower occurrence of abnormal fetal heart rate could be related to improvement of pregnancy management, acquired protection during the interval between the 2 studies, or both.

Intrauterine growth restriction (IUGR): biometric and Doppler assessment

Intrauterine growth restriction (IUGR) is a common complication in pregnancy and influences morbidity and mortality at all stages of life. Historically, the management of IUGR has been dependent on antenatal biophysical testing and umbilical artery Doppler studies. With recent Doppler studies of the fetal central circulation, including intracardiac flows and the ductus venosus, better timing of delivery to minimize morbidity may be possible. This review will provide the reader with tools to diagnose IUGR, more accurately date the IUGR pregnancy with poor dating criteria, and better assess the condition of the IUGR fetus. A brief review of animal models of IUGR is presented to demonstrate research directions for answering human clinical questions and potentially carrying therapeutic intervention from the bench to the bedside.

Perinatal implications of maternal hypertension

Hypertensive disorders of pregnancy are prototypical of maternal conditions associated with reduced uteroplacental blood flow. Hypertensive disorders in pregnancy include chronic hypertension, preeclampsia-eclampsia, superimposed preeclampsia, and gestational hypertension. Pathophysiology of these disorders include deficient uterine vascular modeling in the process of placentation and aberrations of vasomotor regulation. Aberrations of uterine renin-angiotensin system may play a proximate role in the pathogenesis of preeclampsia syndrome. Clinical manifestations are explained in this review based on resultant vasoconstriction and ischemia in systemic and regional circulations. Perinatal implications of hypertensive disorders both in terms of early neonatal outcome and long-term neurodevelopmental effects are described. Methods of antenatal assessment of the fetus and, briefly, principles of clinical management are described.

Fetal adrenal artery velocimetry measurements in appropriate-for-gestational age and intrauterine growth-restricted fetuses

OBJECTIVE

To investigate adrenal artery blood flow in the fetus.

DESIGN AND METHOD

Sixty-two appropriate-for-gestational-age (AGA) and 20 intrauterine growth-restricted (IUGR) fetuses were recruited to this cross-sectional study between 22 and 42 weeks of pregnancy in a tertiary referral fetal medicine unit of a university hospital.

ENDPOINTS

Doppler velocimetry of the fetal adrenal, umbilical (UA), renal and middle cerebral arteries (MCA). Pulsatility index (PI), resistance index (RI), peak systolic velocity (PSV), time-averaged maximum velocity (TAMXV) and cerebroplacental ratio (MCA RI/UA RI; CPR). Obstetric outcome.

RESULTS

The adrenal artery was detected in 82% of the fetuses. All flow velocity waveforms obtained from the adrenal artery indicated low impedance blood flow. No significant changes in PI, RI, PSV and TAMXV occurred with advancing gestation. The blood flow parameters of the adrenal artery did not differ between AGA and IUGR fetuses. In five IUGR fetuses with signs of redistribution of cardiac output in favor of the brain, the adrenal artery velocimetry results were unremarkable. The adrenal artery PI, RI, PSV and TAMXV values were higher in female fetuses than in male fetuses (P < 0.05). A relationship was observed between the velocity measurements and the estimated fetal weight (P < 0.01).

CONCLUSIONS

The fetal adrenal artery could be readily detected. We observed no redistribution of blood flow in favor of the fetal adrenals in IUGR fetuses which were not severely compromised.

Fetal arterial Doppler-IUGR and hypoxia

Vascular resistances of various fetal areas are assessed by Doppler ultrasound. The PI, RI and S/D indices are measured on the cerebral, renal, aortic and umbilical Doppler spectrum. Ratios of these indices based on the comparison of the cerebral (Rc) and the umbilical (Rp) resistances, or carotid (Rcc) and umbilical resistances, or cerebral (Rc) and aortic (Rao) resistances (Rc/Rp or Rp/Rcc, or Rc/Rao), measure the flow redistribution between the placenta and brain. The umbilical resistance indices, when greater than the upper limit of the normal range (> 2sd) are frequently associated with IUGR. (Sensitivity about 65 to 70%). Absent end diastolic flow is most of the time associated with severe IUGR and hypoxia and poor fetal outcome. A fairly good correlation was found between the existence of significantly decreased (< .2.sd) cerebral resistance and the development of post asphyxial encephalopathy in the neonate (Specificity 75% Sensitivity 87%). The earliest detectors of IUGR and hypoxia are the cerebral-umbilical cerebral-carotid, or cerebral-aortic ratios (Sensitivity 85% specificity 90%). When used as predictor of poor perinatal outcome in growth retarded fetuses, the cerebral umbilical ratio shows a sensitivity of 90% compared with 78% of the middle cerebral artery, and 83% for the umbilical artery indices. Changes of this ratio are well correlated with the fetal pO2 changes. The renal flow response to hypoxia depends on the degree of hypoxia. Opposite responses were found in case of moderate, and severe IUGR or hypoxia. Thus, it is too early to conclude if the renal indices are reliable parameters for the evaluation of fetal hypoxia. The sensitivity in predicting IUGR was for the aortic PI: 41% and for the aortic BFC (Blood flow classes): 57%. In predicting delivery for fetal distress, the corresponding values were 76 and 87%, respectively. Because the resistance indices are heart rate-dependent, it is dangerous to draw any conclusion from one single value of any of these parameters. Only several successive measurement of the Doppler indices or of their ratio, may lead to a reliable evaluation of fetal hemodynamics. In the case of significant IUGR with abnormal Doppler indices it is recommended to repeat the Doppler measurements daily both at the cerebral and umbilical or aortic level in order to follow up the fetal flow redistribution which is highly correlated with the fetal pO2 changes.

Twenty-day cerebral and umbilical Doppler monitoring on a growth retarded and hypoxic fetus

In one growth retarded and hypoxic fetus, the cerebral and umbilical hemodynamic changes were assessed (by Doppler), daily over 20 days. The fetal brain was investigated by magnetic resonance imaging (MRI) close to the delivery, and because the fetus died at delivery we performed an anatomical study of the fetal brain. The evolution of the fetal hemodynamics (day by day) was interpreted according to the MRI findings and the clinical findings. During the period of observation (under sustained hypoxia) the fetal deterioration was characterized by: (a) the progressive development of the oligohydramnios (190d), (b) the disappearance of the vascular reactivity (eight successive cerebral resistance index (RI) constant at 194d), (c) the occurrence of fetal heart rate decelerations (199d), and finally (d) the increase of the cerebral vascular resistances with reduction of the brain perfusion (204d). The anatomical study of the brain showed a periventricular congestion however the histology revealed hypoxic lesions like gliosis and a marked vasodilation of the anterior and middle cerebral arteries. Finally in addition to single Doppler measurements performed 1 week before delivery (for prediction of fetal outcome), one can suggest to use the 'loss of fluctuation of the cerebral RI' to identify the beginning of the period of very high risk for the fetus. Such hypothesis may have to be confirmed on a larger number of pathological pregnancies.