The value of Doppler ultrasonography in prolonged pregnancies

Fetal umbilical artery Doppler as a tool for universal third trimester screening: A systematic review and meta-analysis of diagnostic test accuracy

The objective of this study was to investigate the accuracy of universal third trimester umbilical artery (UA) Doppler to predict adverse pregnancy outcome at term. We searched Medline, EMBASE, the Cochrane library and ClinicalTrials.gov from inception to October 2020 and we also analyzed previously unpublished data from a prospective cohort study of nulliparous women, the Pregnancy Outcome Prediction (POP) study. We included studies that performed a third-trimester ultrasound scan in unselected, low or mixed risk populations, excluding studies which only included high risk pregnancies. Meta-analysis was performed using the hierarchal summary receiver operating characteristic curve (HSROC) analysis and bivariate logit-normal models. We identified 13 studies (including the POP study) involving 67,764 pregnancies which met our inclusion criteria. The overall quality was variable and only six studies (N = 5777 patients) blinded clinicians to the UA Doppler result. The summary sensitivity and positive likelihood ratio (LR) for small for gestational age (SGA; birthweight <10th centile) were 21.7% (95% CI 13.2-33.6%) and 2.65 (95% CI 1.89-3.72) respectively. The summary positive LR for NICU admission and metabolic acidosis were 1.35 (95% CI 0.93-1.97) and 1.34 (95% CI 0.86-2.08) respectively. The results were similar in the POP study: associations with SGA (positive LR 2.66 [95% CI 2.11-3.36]) and severe SGA (birthweight <3rd centile; positive LR 3.27 [95% CI 2.29-4.68]) but no statistically significant association with neonatal morbidity. We conclude that third trimester UA Doppler has moderate predictive accuracy for small for gestational age but not for indicators of neonatal morbidity in unselected and low risk pregnancies.

Universal late pregnancy ultrasound screening to predict adverse outcomes in nulliparous women: a systematic review and cost-effectiveness analysis

BACKGROUND

Currently, pregnant women are screened using ultrasound to perform gestational aging, typically at around 12 weeks' gestation, and around the middle of pregnancy. Ultrasound scans thereafter are performed for clinical indications only.

OBJECTIVES

We sought to assess the case for offering universal late pregnancy ultrasound to all nulliparous women in the UK. The main questions addressed were the diagnostic effectiveness of universal late pregnancy ultrasound to predict adverse outcomes and the cost-effectiveness of either implementing universal ultrasound or conducting further research in this area.

DESIGN

We performed diagnostic test accuracy reviews of five ultrasonic measurements in late pregnancy. We conducted cost-effectiveness and value-of-information analyses of screening for fetal presentation, screening for small for gestational age fetuses and screening for large for gestational age fetuses. Finally, we conducted a survey and a focus group to determine the willingness of women to participate in a future randomised controlled trial.

DATA SOURCES

We searched MEDLINE, EMBASE and the Cochrane Library from inception to June 2019.

REVIEW METHODS

The protocol for the review was designed a priori and registered. Eligible studies were identified using keywords, with no restrictions for language or location. The risk of bias in studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. Health economic modelling employed a decision tree analysed via Monte Carlo simulation. Health outcomes were from the fetal perspective and presented as quality-adjusted life-years. Costs were from the perspective of the public sector, defined as NHS England, and the costs of special educational needs. All costs and quality-adjusted life-years were discounted by 3.5% per annum and the reference case time horizon was 20 years.

RESULTS

Umbilical artery Doppler flow velocimetry, cerebroplacental ratio, severe oligohydramnios and borderline oligohydramnios were all either non-predictive or weakly predictive of the risk of neonatal morbidity (summary positive likelihood ratios between 1 and 2) and were all weakly predictive of the risk of delivering a small for gestational age infant (summary positive likelihood ratios between 2 and 4). Suspicion of fetal macrosomia is strongly predictive of the risk of delivering a large infant, but it is only weakly, albeit statistically significantly, predictive of the risk of shoulder dystocia. Very few studies blinded the result of the ultrasound scan and most studies were rated as being at a high risk of bias as a result of treatment paradox, ascertainment bias or iatrogenic harm. Health economic analysis indicated that universal ultrasound for fetal presentation only may be both clinically and economically justified on the basis of existing evidence. Universal ultrasound including fetal biometry was of borderline cost-effectiveness and was sensitive to assumptions. Value-of-information analysis indicated that the parameter that had the largest impact on decision uncertainty was the net difference in cost between an induced delivery and expectant management.

LIMITATIONS

The primary literature on the diagnostic effectiveness of ultrasound in late pregnancy is weak. Value-of-information analysis may have underestimated the uncertainty in the literature as it was focused on the internal validity of parameters, which is quantified, whereas the greatest uncertainty may be in the external validity to the research question, which is unquantified.

CONCLUSIONS

Universal screening for presentation at term may be justified on the basis of current knowledge. The current literature does not support universal ultrasonic screening for fetal growth disorders.

FUTURE WORK

We describe proof-of-principle randomised controlled trials that could better inform the case for screening using ultrasound in late pregnancy.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42017064093.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 15. See the NIHR Journals Library website for further project information.

[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.

Computerised evaluation of fetal heart rate in post-term fetuses: long term variation

Computerised fetal heart rate records were obtained between 1987 and 1993 using the Sonicaid System 8000 for a cross-sectional study of postdates fetal heart rate variation; 567 singleton pregnancies at 41 and 43 weeks provided 1502 records. In all cases gestational age had been verified by ultrasound examination in early pregnancy. The mean minute range of the long term pulse interval variation, which is known to be correlated with fetal oxygenation was found to decrease progressively from an average value of 48.5 ms at 41 weeks to 46.4 ms and 42.4 ms at 42 and 43 or more weeks, respectively. When conservative management of postdate pregnancies is chosen, accurate measurements are needed to follow the evolution of fetal condition. Reference values for calculated pulse interval variation at later gestational ages are now provided.

Association between a low umbilical artery pulsatility index and fetal distress in labor in very prolonged pregnancies

OBJECTIVE

To investigate the association between fetal, umbilical and uterine circulatory changes and adverse perinatal findings in very prolonged pregnancies.

STUDY DESIGN

44 women proceeding to 43 completed weeks of gestation with the intention of a trial of vaginal delivery were studied prospectively with ultrasound Doppler velocimetry. An intensified fetal surveillance was routinely commenced at 42 weeks and only uncomplicated pregnancies were allowed to proceed. The endpoint perinatal measures were oligohydramnios, fetal meconium release, fetal distress in labor and birth asphyxia. Flow variables in different groups were compared with the Mann-Whitney U test, Student's unpaired t-test, Wilcoxon signed-rank matched-pairs test, Fisher's exact test and contingency table analysis, and a two-tailed P value <0.05 was considered statistically significant.

RESULTS

The umbilical artery pulsatility index was significantly lower in cases of fetal meconium release (n=12) and fetal distress (n=7). The umbilical venous flow velocity was significantly lower in cases of meconium, and the fetal aortic volume flow significantly higher in cases of fetal distress. No significant flow changes were found in connection with oligohydramnios (n=5) and birth asphyxia (n=2). Uterine flow was not significantly affected in any group.

CONCLUSIONS

In very prolonged pregnancies, fetal distress in labor was not associated with an increased placental vascular resistance. In contrast to previous reports, the umbilical artery pulsatility index was low in cases of fetal distress and meconium release. The etiology is unknown, but a subclinical fetal hypoxia might have triggered a vasodilation of placental vessels. Vasodilation at an unchanged volume flow could also explain the decrease of umbilical venous flow velocity. The increased aortic volume flow indicates an increase of cardiac output in fetuses later developing distress in labor.