Fetal middle cerebral artery blood flow during normal active labour and in labour with variable decelerations

[Per partum acidosis: Interest and feasibility of cerebral Doppler during labor]

OBJECTIVES

To evaluate feasibility and interest of fetal cerebral Doppler during labor and the link with fetal pH to predict perinatal fetal asphyxia.

METHODS

Our prospective study in a university perinatal center, included patients during labor. There were no risk factors during pregnancy and patients were included after 37 weeks of pregnancy. For each patient an ultrasound with cerebral Doppler was done concomitant to a fetal scalp blood sample. We collected maternal and fetal characteristics as well as cervix dilatation, fetal heart rate analysis and fetal presentation.

RESULTS

Among 49 patients included over a period of 4 months, cerebral Doppler failed in 7 cases (11%). Majority of failure occurred at 10cm of dilatation (P=0.007, OR=14.1 [1.483; 709.1275]). Others factors like: maternal age, body mass index, parity, history of C-Section were not associated with higher rate of failure. We did not found either significant correlation between cerebral fetal Doppler and pH on fetal scalp blood sample (r=0.15) nor pH at cord blood sample (r=0.13). No threshold of cerebral Doppler is significant for fetal asphyxia prediction.

CONCLUSION

Fetal cerebral Doppler is feasible during labor with a low rate of failure but not a good exam to predict fetal acidosis and asphyxia.

Study of uterine and fetal hemodynamics in response to labor induction with dinoprostone in prolonged pregnancies with normal amniotic fluid and oligohydramnios

OBJECTIVE

We investigated the effects of labor induction with Dinoprostone on uteroplacental and fetal circulations with Doppler velocimetry in prolonged pregnancies with and without oligohydramnios.

METHODS

We performed Doppler evaluations of Uterine A, Umbilical A and Middle Cerebral A. (MCA) in 117 patients (27 associated with oligohydramnios) just before and 6 h after the administration of Dinoprostone. We compared two groups with Mann Whitney U Test and Independent Sample T Test.

RESULTS

Uterine Artery Doppler indices of both groups obtained before the medication were compared. All indices were within normal range; however Umbilical A. S/D and PI were higher in oligohydramnios group, approaching statistical significance (p=0.07 for S/D and p=0.03 for PI). All of the Uterine A. Doppler indices significantly increased after the administration of Dinoprostone ovule in normal amniotic fluid index (AFI) group (p=0.00). Doppler indices of the other arteries in this group did not change significantly. Similarly, none of the Doppler indices of all investigated arteries in oligohydramnios group changed significantly. Changes in all measured Doppler indices were minor and similar in both groups.

CONCLUSIONS

Labor induction with Dinoprostone in prolonged pregnancies complicated with oligohydramnios is as safe and effective as it is in prolonged pregnancies with normal AFI.

Can anomalies of fetal brain circulation be useful in the management of growth restricted fetuses?

Assessment of the fetal cerebral circulation provides important information on the hemodynamic changes associated with chronic hypoxia and intrauterine growth restriction. Despite the incorporation of new US parameters, the landmark for the fetal brain hemodynamic evaluation is still the middle cerebral artery. However, new vascular territories, such as the anterior and posterior cerebral arteries, might provide additional information on the onset of the brain sparing effect. The fractional moving blood volume estimation and three-dimensional power Doppler ultrasound indices are new techniques that seem to be promising in identifying cases at earlier stages of vascular deterioration; still, they are not available for clinical application and more information is needed on the reproducibility and advantages of three-dimensional power Doppler ultrasound blood flow indices. In the past, the brain sparing effect was considered as a protective mechanism; however, recent information challenges this concept. There is growing evidence of an association between brain sparing effect and increased risk of abnormal neurodevelopment after birth. Even in mild late-onset intrauterine growth restriction affected fetuses with normal umbilical artery blood flow, increased cerebral blood perfusion can be associated with a substantial risk of abnormal neuroadaptation and neurodevelopment during childhood.

Doppler impedance changes at the fetal brain vessels in a pregnancy affected with a multiple combination of uteroplacental anomalies

A fetus with a very rare five-fold combination of uteroplacental anomalies, bicornuate uterus, short cervix with cervical incompetence, multilobed placenta succenturiata, accessory cotyledon within the cervical funneling, and umbilical cord insertion into the anomalous cervical cotyledon, presented an early and marked decrease at the vertebral and middle cerebral arteries Doppler resistances. This cerebral low-impedance state, usually found before labor, and considered an adaptive mechanism developed to protect the fetus at term from labor asphyxia, was present for an unknown reason at 20 weeks. After the patient was treated with vaginal progesterone, the cervix shortening improved and markedly, at the same time, the cerebral vascular resistances increased and maintained an adequate for gestational age impedance until delivery at 34 weeks. As the described uteroplacental anomalies determined a high risk of preterm delivery, due to cervical dilation, cord compresion, and placental haemorrhage, these fluctuating brain vascular changes might be the result of the fetal adaptation to the changes preceding an imminent delivery.

[Management of post-term pregnancies: the role for AFI, biophysical score and doppler]

OBJECTIVE

To evaluate the role of ultrasound and doppler assessment in the management of prolonged pregnancies and to state its modalities.

METHOD

Medline, PubMed, embase and the Cochrane library were searched using terms prolonged pregnancy, post date pregnancy amniotic fluid, ultrasound assessment, doppler, biophysical profile.

RESULTS

Single deepest vertical pool measurement is the method of choice of the assessment of amniotic fluid. Indeed, when this method was used, significantly fewer case of oligohydramnios were diagnosed and fewer women had inductions of labor. However, this method is not superior to the amniotic fluid index in the prevention of poor perinatal outcomes. There is a significant difference in the incidence of fetal distress, meconium stained fluid and caesarean section for fetal distress when the amniotic fluid is reduced as compared with normal amniotic fluid. However, sensibility and predictive positive value of oligohydramnios to predict poor perinatal outcomes is moderate. Similary, in most studies, diagnosis of an abnormal uterine, umbilical, aortic or cerebral blood flow doppler was associated with a weak prediction of a poor perinatal outcome. Therefore, we do not recommend its use in management of prolonged pregnancy. There were significantly more diagnosis of oligoamnios and more abnormal antenatal monitoring results in the modified biophysical profile group as compared with the group managed with only single deepest pool but no differences in cord blood gases, neonatal outcome, or in outcomes related to labour and delivery were noted between the two groups. Therefore, biophysical profile including AFI offers no advantage in detecting adverse outcomes and may cause more interventions.

CONCLUSION

Close monitoring of fetal condition including assessment of amniotic fluid by single deepest pool twice a week from 41 weeks of gestation is recommended in the management of prolonged pregnancy. Induction of labor could be considered when oligohydramnios is diagnosed by single deepest pool less than 2 cm.

Evaluation of fetal cerebrovascular circulation and brain development: the role of ultrasound and Doppler

The human fetal brain is protected from pressure changes by autoregulation of the cerebral circulation. However, antenatal intrauterine cerebrovascular events are found to play an important role in the pathogenesis of perinatal brain damage. Changes in placental vascular resistance, cardiac contractibility, vessel compliance, and blood viscosity alter the normal dynamics of fetal cerebral circulation. The introduction of various sonographic techniques and the collection of data from the arterial and venous cerebral circulation provide a powerful tool for the evaluation of physiological and pathological hemodynamic events. Anatomic and physiological considerations of cerebral vasculature in healthy and disease states are relevant in studying brain development and variations in fetal brain blood perfusion. The major role of ultrasound and Doppler modalities in the evaluation of fetal cerebrovascular circulation is enabled by implementation of these considerations. Changes in flow characteristics in fetal cerebral vasculature can be used for clinical decision making in situations of fetal compromise, such as growth restriction and anemia.

Uterine activity: implications for the condition of the fetus

AIM

The aim of this review is to provide more insight in the fetal mechanisms as a response to uterine contractions and to emphasize the importance of correct assessment of uterine activity (UA) patterns during labor.

STUDY RESULTS

UA causes a decreased flow through the uterine artery. In the healthy uncompromised fetus, this will not cause fetal acidemia. The fetus has developed certain protection mechanisms to survive labor; (1) During a contraction, fetal preload increases and enables the fetus to maintain a constant blood flow through the umbilical artery and (2) UA increases the blood flow in the fetal middle cerebral artery, i.e., a brain sparing effect. The shortcoming of those protection mechanisms in the compromised fetus and in case of excessive UA increases the risk of adverse fetal outcome. The brain sparing effect will become more pronounced to compensate for the decreased umbilical artery blood flow and fetal oxygen saturation. Maintenance of normal UA, especially a sufficiently long relaxation time, is essential so that the supply of well oxygenated maternal blood to the intervillous space will be restored and the fetal cerebral oxygen saturation can remain stable.

CONCLUSION

Adequate UA monitoring is a prerequisite for proper reading and interpretation of cardiotocograms. It alarms in cases of excessive UA and can help to prevent fetal acidemia. Uterine contraction monitoring deserves full attention in daily obstetric practice.

Acute centralization of blood flow in compromised human fetuses evoked by uterine contractions

BACKGROUND

During fetal hypoxia blood is redistributed to the brain ('brain-sparing'). Sequential changes of the cerebral and placental circulation in parallel in comparisons between basal conditions and acute hypoxic stress have not yet been thoroughly studied in human fetuses.

AIM

To explore acute fetal middle cerebral artery (MCA) circulatory changes relative to umbilical artery (UA) blood flow in a clinical experimental model with hypoxic stress provoked by uterine contractions during an oxytocin challenge test (OCT).

STUDY DESIGN

Prospective comparative between imminently compromised (OCT positive) and un-compromised (OCT negative) fetuses.

SUBJECTS AND METHODS

82 term pregnancies suspected of intrauterine growth restriction were exposed to simultaneous electronic fetal heart rate monitoring and Doppler recordings of pulsatility index (PI) in the UA and MCA during basal conditions and during uterine contractions and relaxations at an OCT.

OUTCOME MEASURES

Sequential changes of UA and MCA PI, OCT positive vs. negative cases. Nonparametric statistics with a P < 0.05 considered significant.

RESULTS

The UA PI was significantly higher in OCT positive cases (N = 10) compared with OCT negative cases (N = 72) during uterine contractions and relaxations, but not during basal measurements. During contractions and relaxations the MCA PI decreased significantly in both groups (brain-sparing), but significantly more in OCT positive cases.

CONCLUSIONS

During acute hypoxic stress, changes towards a centralization of blood flow to the brain develop in imminently compromised (OCT positive) fetuses at an expense of the umbilicoplacental blood flow, and the brain-sparing flow is more pronounced than in un-compromised (OCT negative) fetuses.

Reference ranges for umbilical and middle cerebral artery pulsatility index and cerebroplacental ratio in prolonged pregnancies

OBJECTIVE

To construct normal ranges for umbilical artery pulsatility index (UA PI), middle cerebral artery pulsatility index (MCA PI) and cerebroplacental ratio (CPR) in prolonged pregnancies according to strict methodological criteria using polynomial regression analysis.

METHODS

This was a retrospective, cross-sectional observational study involving 140 women, 10 women for each gestational day between 287 and 300 days of gestation. Fetal Doppler parameters were assessed to construct normal reference ranges for UA PI and MCA PI. CPR was calculated as a ratio of MCA PI/UA PI.

RESULTS

Mathematical modeling of the data demonstrated that the optimal fit was a linear polynomial one. Mean, 5th and 95th centiles were calculated for UA, MCA and CPR and centile curves from the regression analysis were constructed.

CONCLUSIONS

Reference ranges for UA PI, MCA PI and CPR in prolonged pregnancies have been constructed. MCA PI shows a wider range than previously reported in the literature.

Middle cerebral artery Doppler indices at different sites: prediction of umbilical cord gases in prolonged pregnancies

OBJECTIVES

To assess the value of middle cerebral artery Doppler indices obtained from different sampling sites in predicting umbilical cord gases at delivery in prolonged pregnancies.

METHODS

This was a prospective study of consecutive pregnant women referred for prolonged-pregnancy surveillance. The predictive value of distal and proximal middle cerebral artery Doppler indices for cord blood gases was evaluated in women who delivered within 48 h of their last antenatal test using stepwise multiple regression.

RESULTS

There was a significant linear correlation between proximal and distal middle cerebral artery pulsatility indices (R = 0.777; P < 0.0001), the mean values being 1.49 (SD, 0.45) and 1.56 (SD, 0.47), respectively. There was also a linear correlation between proximal and distal cerebroplacental ratios (R = 0.68; P < 0.0001), the mean values being 1.85 (SD, 1.96) and 1.92 (SD, 1.89), respectively. The stepwise multiple regression analysis for umbilical artery pH showed that once the distal middle cerebral artery pulsatility index was introduced into the model, the addition of any variable did not result in a significant improvement of the predictive capacity. The model showed a coefficient of determination (R(2)) of 0.079. There was a significant correlation between umbilical artery pO(2) and both proximal middle cerebral artery pulsatility index (positive) and the occurrence of elective Cesarean section (negative). This model accounted for 21% of the variance (R(2) = 0.21). No other variables added any significant prediction for pO(2).

CONCLUSIONS

In post-term pregnancies the proximal middle cerebral artery pulsatility index significantly predicts umbilical artery pO(2) at delivery but does not predict pH. There is a weak association between distal middle cerebral artery pulsatility index and pH but, as this only explains 8% of the variance, it is of little clinical value.

The relation between pre-eclampsia at term and neonatal encephalopathy

OBJECTIVES

To determine whether pre-eclampsia, hypothesised to be an inflammatory condition, is associated with fever in term labour, and confirm and examine the reported association of pre-eclampsia at term with neonatal encephalopathy.

DESIGN

Prospective cohort study.

SETTING

A Dublin teaching hospital.

PARTICIPANTS

6163 women in labour with singleton pregnancies at term at low risk for intrapartum hypoxia, recruited to a randomised trial examining the effect of admission cardiotocography on neonatal outcome.

RESULTS

Pre-eclampsia was associated with maternal fever > 37.5 degrees in labour (odds ratio (OR) 3.39, 95% confidence interval (CI) 2.1 to 5.4); this was independent of obstetric intervention (adjusted OR 2.07, 95% CI 1.24 to 3.47). Pre-eclampsia was associated with neonatal encephalopathy (OR 25.5, 95% CI 8.4 to 74.7); this too was independent of obstetric intervention (adjusted OR 18.5, 95% CI 5.9 to 58.1). Cord arterial pH values were significantly lower in pre-eclamptics (7.20 v 7.24), although severe cord acidaemia was not significantly more common (OR 2.91, 95% CI 0.7 to 9.9). The association of pre-eclampsia with encephalopathy was independent of maternal fever (adjusted OR 16.5, 95% CI 5.1 to 54) and cord acidaemia (adjusted OR 13.5, 95% CI 3.2 to 56.7).

CONCLUSIONS

The association of pre-eclampsia with maternal fever at term supports the hypothesis that pre-eclampsia is an inflammatory condition. The association of pre-eclampsia with neonatal encephalopathy is independent of obstetric intervention and cannot be explained by either acidaemia or maternal fever. A systemic inflammatory response in the fetus, perhaps secondary to oxidative stress, could explain the link between maternal pre-eclampsia and neonatal encephalopathy, and this may occur through cerebral vasoconstriction.

Intrapartum umbilical artery Doppler velocimetry as a predictor of adverse perinatal outcome: a systematic review

OBJECTIVE

To evaluate the diagnostic prediction of intrapartum umbilical artery Doppler velocimetry for adverse perinatal outcomes using systematic quantitative overview of the available literature.

DESIGN

Online searching of MEDLINE database (January 1966-September 1997), scanning of bibliography of known primary and review articles, review of recent journal issues and that from personal files. Study selection, assessment of study quality and data extraction were all performed in duplicate under masked conditions.

PARTICIPANTS

2700 women (unselected, low, high, and combined low and high obstetric risk populations) included in eight studies selected for meta-analyses.

MAIN OUTCOME MEASURES

Likelihood ratios (LRs) for positive and negative test results were generated for the following outcome measures: Apgar scores < 7 at 1 and 5 minute following delivery, small for gestational age fetus; intrapartum fetal heart rate abnormality, umbilical arterial acidosis at delivery; and caesarean section for fetal distress.

RESULTS

For Apgar score < 7 at 1 minute following delivery, the pooled LR was 2.5 (95% CI 1.7-3.7) for a positive test and 1.0 (95% CI 0.9-1.1) for a negative test result. A positive test predicted an Apgar score < 7 at 5 minute following delivery with a pooled LR of 1.3 (95% CI 0.4-4.1) while a negative test had a pooled LR of 1.0 (95% CI 0.8-1.2). For the prediction of a small for gestational age fetus, the pooled LR was 3.4 (95% CI 2.3-5.1) for a positive test and 0.9 (95% CI 0.8-1.0) for a negative test. The prediction for fetal heart rate abnormality during labour was similarly disappointing: the pooled LR for a positive test result was 1.4 (95% CI 0.9-1.2) whereas a negative test result generated a pooled LR of 0.9 (95% CI 0.9-1.0). With umbilical acidosis at delivery, the pooled LR was 1.6 (95% CI 1.1-2.5) for a positive test and 1.1 (95% CI 1.0-1.2) for a negative test. The LRs for the prediction of caesarean section for fetal distress were 4.1 (95% CI 2.7-6.2) for a positive test result and 0.9 (95% CI 0.8-1.0) for a negative test result.

CONCLUSION

Intrapartum umbilical artery Doppler velocimetry is a poor predictor of adverse perinatal outcomes.

Intra- and early postpartum ultrasonography: a review. Part II

Part II is a continuation of the preceding segment, which appeared in the previous issue (Survey 1998;53:000-000). This part presents data pertaining to ultrasound-guided procedures (invasive and noninvasive), physiology (fetal behavior), intrapartum hemorrhage, the third stage of labor, post-partum hemorrhage, and postcaesarean ultrasonography. In addition, this article includes data regarding nonobstetric ultrasound including anesthesiology, catheter placement, venous air embolism, effect of epidural anesthesia on uterine blood flow, and urinary retention. Finally, this part presents ultrasonographic data of the maternal cerebral circulation in preeclampsia/eclampsia and of the maternal deep venous system.

Prenatal ultrasonographic assessment of the middle cerebral artery: a review

Published reports, case studies, and articles regarding ultrasonographic morphology, physiology, and pathophysiology of the fetal middle cerebral artery obtained from a MEDLINE search from 1966 through January 1997 were reviewed. Both transabdominal and transvaginal color Doppler ultrasonographic modalities may be used to assess fetal middle cerebral artery flow hemodynamics. Altered middle cerebral artery flow velocities may be noted in various medical conditions that include various behavioral states, term and preterm labor, maternal medications (anesthesia, tocolytics), fetal compromise (growth restriction and hypoxia), twin-twin transfusion syndrome, invasive diagnostic procedures (amniocentesis and fetal blood sampling), fetal anemia and transfusion, in addition to intracranial fetal lesions (congenital anomalies and hemorrhage). In summary, knowledge of Doppler flow velocity of the fetal middle cerebral artery may assist prenatal diagnosis and management of complicated pregnancies.

Middle cerebral artery velocimetry as a predictor of hypoxemia in fetuses with increased resistance to blood flow in the umbilical artery

About half of all fetuses with increased resistance to blood flow, but with still detectable diastolic blood velocity in the umbilical artery (UA), show signs of imminent asphyxia during labour indicating a need for operative delivery. Fetal brain-sparing during hypoxia is characterized by an increase in diastolic and mean blood flow velocity in the middle cerebral artery (MCA). The aim of this study was to assess whether MCA blood velocity in pregnancies with increased resistance to blood flow in the feto-placental circulation could predict the development of fetal asphyxia during labour. Fifty pregnant women with signs of increased feto-placental vascular resistance between 31 and 42 weeks of gestation were studied serially by Doppler ultrasound and the last examination was correlated to perinatal outcome. The MCA pulsatility index (PI), cerebroplacental PI ratio and mean MCA blood velocity were calculated and correlated to fetal outcome. Fetal brain-sparing was defined as MCA PI < mean -2 S.D., cerebroplacental PI ratio < 1.08 and mean MCA blood velocity >mean + 2 S.D. No significant association was found between signs of fetal brain-sparing and the perinatal outcome. Among fetuses with signs of increased resistance to flow in the umbilical artery, velocimetry of the middle cerebral artery did not identify those that would not withstand the strain of labour.

Doppler information pertaining to the intrapartum period

The aim of the study was to evaluate the use of color-Doppler velocimetry during the labor. 325 intrapartal measurements of the umbilical artery, fetal aorta, middle cerebral artery and arcuate arteries were performed in a group of 105 patients. The resistance index (RI) and pulsatility index (PI) were measured. During the active labor the RI and PI of the umbilical artery remained unchanged. The impedance in arcuate arteries have increased (p < 0.05). The RI and PI of the middle cerebral artery showed non significantly increased mean values when compared with the corresponding values during pregnancy. But, a short term, transitory decreased impedance is registered during the decrement slope of contraction. Since fetal outcome was normal in all newborns, these changes are considered as physiologic.

Cerebral blood flow velocity in term newborns following intrapartum fetal asphyxia

Twenty-six term newborns with intrapartum fetal asphyxia, determined biochemically (umbilical artery base deficit > 12 mmol/l), were compared with 59 normal newborns to determine the effect of intrapartum fetal asphyxia on newborn blood pressure and cerebral blood flow velocity following delivery. Cerebral blood flow velocity observations with concurrent measures of blood pressure and heart rate were obtained during the 24 h after delivery and after 24 h. After delivery, diastolic blood pressure in the newborns of the asphyxia group was significantly greater than that of the newborns of the normal group and this difference persisted after 24 h. Cerebral blood flow velocity in the newborns of the asphyxia group was of the same order as that of the newborns of the normal group during the 24 h after delivery. However, there was a significant increase in both peak systolic and end-diastolic blood flow velocity after 24 h. The duration of metabolic acidosis may be a factor in the occurrence of this delayed cerebral blood flow velocity response. Observations of cerebral blood flow velocity should be continued for more than 24 h following delivery to determine the effect of intrapartum fetal asphyxia.

Post-term pregnancies with normal cardiotocographs and amniotic fluid columns: the role of Doppler evaluation in predicting perinatal outcome

OBJECTIVE

To study the role of Doppler ultrasound examination in predicting an abnormal perinatal outcome, among post-term pregnancies uncomplicated by an abnormal non-stress test (NST) or reduced amount of amniotic fluid.

DESIGN

A prospective study.

SETTING

High-risk pregnancy unit, Hadassah Mt. Scopus University Hospital, Jerusalem.

SUBJECTS

Seventy-eight women with confirmed gestational age of > 287 days, who had normal initial evaluation and unfavourable cervical examination.

INTERVENTIONS

Doppler flow velocity waveforms were recorded from the umbilical and middle cerebral arteries, and from the descending thoracic aorta.

MAIN OUTCOME MEASURES

Correlation between Doppler measurements and data regarding delivery.

RESULTS

Women who developed signs of fetal distress during labour, or who required intervention because of fetal distress, had elevated umbilical artery systolic/diastolic ratio, decreased middle cerebral artery pulsatility index, and decreased time average aortic blood flow velocity. Umbilical artery Doppler measurements could significantly predict the need for intervention due to fetal distress.

CONCLUSIONS

Doppler examination of uncomplicated post-term pregnancies may identify patients with normal results as having a low risk of developing fetal distress during labour. Patients with abnormal Doppler results are prone to need intervention following fetal distress in labour.