Reference ranges for Doppler indices of umbilical and fetal middle cerebral arteries and cerebroplacental ratio: systematic review

Cerebroplacental ratio in predicting adverse perinatal outcome: a meta-analysis of individual participant data

Objective

To investigate if cerebroplacental ratio (CPR) adds to the predictive value of umbilical artery pulsatility index (UA PI) alone – standard of practice – for adverse perinatal outcome in singleton pregnancies.

Design and setting

Meta‐analysis based on individual participant data (IPD).

Population or sample

Ten centres provided 17 data sets for 21 661 participants, 18 731 of which could be included. Sample sizes per data set ranged from 207 to 9215 individuals. Patient populations varied from uncomplicated to complicated pregnancies.

Methods

In a collaborative, pooled analysis, we compared the prognostic value of combining CPR with UA PI, versus UA PI only and CPR only, with a one‐stage IPD approach. After multiple imputation of missing values, we used multilevel multivariable logistic regression to develop prediction models. We evaluated the classification performance of all models with receiver operating characteristics analysis. We performed subgroup analyses according to gestational age, birthweight centile and estimated fetal weight centile.

Main outcome measures

Composite adverse perinatal outcome, defined as perinatal death, caesarean section for fetal distress or neonatal unit admission.

Results

Adverse outcomes occurred in 3423 (18%) participants. The model with UA PI alone resulted in an area under the curve (AUC) of 0.775 (95% CI 0.709–0.828) and with CPR alone in an AUC of 0.778 (95% CI 0.715–0.831). Addition of CPR to the UA PI model resulted in an increase in the AUC of 0.003 points (0.778, 95% CI 0.714–0.831). These results were consistent across all subgroups.

Conclusions

Cerebroplacental ratio added no predictive value for adverse perinatal outcome beyond UA PI, when assessing singleton pregnancies, irrespective of gestational age or fetal size.

Tweetable abstract

Doppler measurement of cerebroplacental ratio in clinical practice has limited added predictive value to umbilical artery alone.

Doppler measurement of cerebroplacental ratio in clinical practice has limited added predictive value to umbilical artery alone.

International gestational age-specific centiles for umbilical artery Doppler indices: a longitudinal prospective cohort study of the INTERGROWTH-21st Project

BACKGROUND

Reference values for umbilical artery Doppler indices are used clinically to assess fetal well-being. However, many studies that have produced reference charts have important methodologic limitations, and these result in significant heterogeneity of reported reference ranges.

OBJECTIVES

To produce international gestational age-specific centiles for umbilical artery Doppler indices based on longitudinal data and the same rigorous methodology used in the original Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project.

STUDY DESIGN

In Phase II of the INTERGROWTH-21st Project (the INTERBIO-21st Study), we prospectively continued enrolling pregnant women according to the same protocol from 3 of the original populations in Pelotas (Brazil), Nairobi (Kenya), and Oxford (United Kingdom) that had participated in the Fetal Growth Longitudinal Study. Women with a singleton pregnancy were recruited at <14 weeks' gestation, confirmed by ultrasound measurement of crown-rump length, and then underwent standardized ultrasound every 5±1 weeks until delivery. From 22 weeks of gestation umbilical artery indices (pulsatility index, resistance index, and systolic/diastolic ratio) were measured in a blinded fashion, using identical equipment and a rigorously standardized protocol. Newborn size at birth was assessed using the international INTERGROWTH-21st Standards, and infants had detailed assessment of growth, nutrition, morbidity, and motor development at 1 and 2 years of age. The appropriateness of pooling data from the 3 study sites was assessed using variance component analysis and standardized site differences. Umbilical artery indices were modeled as functions of the gestational age using an exponential, normal distribution with second-degree fractional polynomial smoothing; goodness of fit for the overall models was assessed.

RESULTS

Of the women enrolled at the 3 sites, 1629 were eligible for this study; 431 (27%) met the entry criteria for the construction of normative centiles, similar to the proportion seen in the original fetal growth longitudinal study. They contributed a total of 1243 Doppler measures to the analysis; 74% had 3 measures or more. The healthy low-risk status of the population was confirmed by the low rates of preterm birth (4.9%) and preeclampsia (0.7%). There were no neonatal deaths and satisfactory growth, health, and motor development of the infants at 1 and 2 years of age were documented. Only a very small proportion (2.8%-6.5%) of the variance of Doppler indices was due to between-site differences; in addition, standardized site difference estimates were marginally outside this threshold in only 1 of 27 comparisons, and this supported the decision to pool data from the 3 study sites. All 3 Doppler indices decreased with advancing gestational age. The 3rd, 5th 10th, 50th, 90th, 95th, and 97th centiles according to gestational age for each of the 3 indices are provided, as well as equations to allow calculation of any value as a centile and z scores. The mean pulsatility index according to gestational age = 1.02944 + 77.7456*(gestational age)-2 - 0.000004455*gestational age3.

CONCLUSION

We present here international gestational age-specific normative centiles for umbilical artery Doppler indices produced by studying healthy, low-risk pregnant women living in environments with minimal constraints on fetal growth. The centiles complement the existing INTERGROWTH-21st Standards for assessment of fetal well-being.

Longitudinal Doppler references for monochorionic twins and comparison with singletons

OBJECTIVES

To construct monochorionic (MC) twin-specific longitudinal Doppler references for umbilical artery pulsatility index (UA-PI), middle cerebral artery (MCA) PI and peak systolic velocity (PSV) and ductus venosus (DV) PI derived from a strictly selected cohort of uncomplicated MC twins. The secondary aim of the study was to compare our findings with singleton reference charts.

METHODS

A retrospective evaluation was made of all consecutive uncomplicated MC twin pregnancies referred to our Unit from 2010 to 2018. Fortnightly serial examinations were performed of UA-PI, MCA-PI, MCA-PSV and DV-PI, according with the clinical protocol, from 20 to 37 weeks of gestation. We included cases with at least four ultrasound examinations, delivery at our hospital and complete neonatal follow up. A two-step method was used to trace the estimated centile curves: estimation of the median was performed with appropriate fractional polynomials by a multilevel model and estimation of the external centiles through the residuals (quantile regression). The comparison with singletons was made by plotting the references derived from the present study on the referred charts commonly used for singletons.

RESULTS

The study group comprised 150 uncomplicated MC twin pairs. Estimated centiles (3rd, 5th, 10th, 50th, 90th, 95th, 97th) of UA-PI, MCA-PI, MCA-PSV and DV-PI in function of the gestational age are presented. The comparison with singletons showed substantial differences, with higher UA-PI and lower MCA-PI and PSV median values in MC twins. Median DV PI values were similar to the values for singletons, while the upper centiles were higher in MC twins.

CONCLUSIONS

This study sets out MC twin-specific longitudinal references for UA-PI, MCA-PI, MCA-PSV and DV-PI derived from the largest series of uncomplicated MC twin pregnancies presently available. The comparison with singleton reference values underscores the deviation from physiology that is intrinsic to these unique pregnancies and supports the need for MC twin-specific charts.

Local cerebroplacental ratio reference ranges are better predictors for adverse delivery outcomes in normal weight fetuses during pregnancy

Objective: To evaluate the predictive value of local versus external cerebroplacental ratio (CPR) reference ranges for delivery outcomes in low-risk pregnancies.Methods: A retrospective analysis of all feto-maternal demographic and biometric data in fetuses with normal estimated fetal weight (EFW) and a CPR examination between the years 2014-2019, in a university medical center. The study group included healthy singleton pregnancies from 32-week gestation, with an examination-to-delivery interval of <31 days. The three models compared two thresholds: <5th percentile (CPR 1, CPR 3) and <10th percentile (CPR2). The CPR1 and CPR2 models both use local CPR reference ranges, while the CPR3 model uses an external CPR reference range. The main outcome was predictive accuracy for urgent cesarean delivery (CD), operative delivery (OD), and composite outcome (CO), defined as an Apgar score of <7, fetal blood pH < 7.1 or admission to the neonatal intensive care unit (NICU).Results: Overall, 410 low-risk pregnancies with normal weight fetuses were enrolled in the study. All three CPR models turned out to be significant predictors of CD, with an odds ratio (OR) of 9, 95% CI (2.7-27), p < .001 for CPR1, and an OR of 2.9, 95% CI (1.1-7.4), p < .04 for CPR2, and an OR of 3.4, 95% CI (1.7-6.8), p < .001 for CPR3. All the three models were also found to be predictors of OD, and an OR of 6.9, 95% CI (2.1-22) p < .04 for CPR1, and an OR of 2.8, 95% CI (1.2-6.7), p < .04 for CPR2, and an OR of 2.8, 95% CI (1.4-5.3) p < .01 for CPR3. The positive predictive values (PPV) for CD and OD were both 50% for CPR1, versus 28% and 26% in CPR2, and 24% and 25% in CPR3. The negative predictive value (NPV) was similar, around 88% in all three models. None of the models were found to be significant predictors for CO.Conclusions: A CPR model based on local reference ranges and <5th percentile cutoffs showed the highest PPV for CD and OD. The calculation of local references for CPR should be encouraged.

Third-trimester Reference Ranges for Cerebroplacental Ratio and Pulsatility Index for Middle Cerebral Artery and Umbilical Artery in Normal-growth Singleton Fetuses in the Israeli Population

BACKGROUND

The ratio between the fetal umbilical artery pulsatility index (UA-PI) and the middle cerebral artery pulsatility index (MCA-PI) is termed the cerebroplacental ratio (CPR). The CPR represents fetal blood flow redistribution at the early stages of placental insufficiency; moreover, it has predictive value for adverse intrapartum and neonatal outcomes. However, internationally accepted reference ranges for CPR are lacking.

OBJECTIVE

This study sought to establish UA-PI, MCA-PI, and CPR reference ranges in low-risk, normal-growth singleton fetuses during the third trimester of pregnancy.

METHODS

A retrospective cohort cross-sectional study was performed in the obstetrics ultrasound unit of a university hospital in Israel. We reviewed all fetal and maternal electronic records of pregnant women referred for ultrasound assessment during the third trimester between January 2014 and January 2019. We included only singleton pregnancies with normal anatomy scans and a normal third-trimester estimated fetal weight. The UA-PI, MCA-PI, and CPR reference ranges were reconstructed for each of the vessels for each gestational age between 29 and 41 weeks.

RESULTS

A total of 560 pregnancies met the inclusion criteria. Satisfactory waveforms and measurements were obtained in all cases. At least 18 women enrolled at each gestational week. The MCA-PI and CPR values showed a similar parabolic curve during the third trimester of pregnancy, with a peak value at 32 and 33 gestational weeks, respectively. The UA-PI showed a linear and gradual decrease over the gestational age.

CONCLUSIONS

In this study we established UA-PI, MCA-PI, and CPR reference ranges in low-risk, normal-growth singleton fetuses during the third trimester based on the Israeli population.

Intra- and Interobserver Reproducibility of Third Trimester Middle Cerebral Artery Pulsatility Index Measurement: A Prospective Cross-Sectional Study

BACKGROUND

Middle cerebral artery (MCA) pulsatility index (PI) Doppler in the third trimester of pregnancy is increasingly used.

OBJECTIVES

The aim of the study was to investigate intra- and interobserver reproducibility of MCA PI in the third trimester.

METHOD

Singleton pregnancies between 30+0 and 40+0 weeks were recruited. MCA Doppler velocimetry measurements were performed prospectively, independently, and blindly. Intra- and interobserver reproducibility was assessed by concordance correlation coefficient (CCC) and intraclass correlation coefficient (ICC); Bland-Altman plots were built, and limits of agreement (LoA) were calculated. Results were interpreted according to the cutoff set by the True Reproducibility of Ultrasound Techniques Review.

RESULTS

We enrolled 101 patients. ICCs for intraobserver reproducibility were 0.84 and 0.78 for raw values and percentiles, respectively; CCCs were 0.72 and 0.64. For interobserver reproducibility ICCs were 0.84 and 0.78, CCCs 0.72 and 0.63. According to the chosen criteria, these values show a poor-moderate reproducibility of third trimester MCA PI. Cohen's Kappa coefficients were 0.59 and 0.42, indicating a moderate agreement in discriminating normal and abnormal values.

CONCLUSIONS

Intra- and interobserver reproducibility of third trimester MCA PI, as assessed by ICC, CCC, and LoA, is far from satisfactory. This should be taken into account before taking clinical decisions.

The value of introducing cerebroplacental ratio (CPR) versus umbilical artery (UA) Doppler alone for the prediction of neonatal small for gestational age (SGA) and short-term adverse outcomes

OBJECTIVE

To compare the role of umbilical artery (UA) Doppler versus CPR in the prediction of neonatal SGA and short-term adverse neonatal outcome in a high-risk population.

STUDY DESIGN

We conducted a prospective study on women referred for fetal growth ultrasounds between 26 and 36 weeks of gestation and with an EFW <20th percentile by Hadlock standard. UA and middle cerebral artery (MCA) Doppler assessments were performed. Abnormal UA Doppler was defined as: pulsatility index (PI) above the 95th percentile and absent or reverse end-diastolic flow. The CPR, calculated as a ratio of the MCA PI by the UA PI, was defined as low if <1.08. The primary outcome was the sensitivity and specificity of the two Doppler assessments to predict neonatal SGA, defined as birthweight <10th percentile by using Alexander curves. The secondary outcomes included umbilical cord arterial pH <7.10, Apgars at 5 minutes <7, NICU admission, respiratory distress syndrome (RDS), hypoglycemia or a composite including any of these secondary outcomes. Chi-square was performed for statistical analysis.

RESULTS

Of the 199 women meeting inclusion criteria, 94 (47.2%) had SGA and 68 (34.2%) had a composite adverse outcome. A total of seven pregnancies with FGR had a low CPR. Abnormal UA Doppler showed a better sensitivity for predicting SGA and adverse neonatal outcomes with comparable specificity to low CPR. The area under the ROC curve (AUC) using abnormal UA Doppler for predicting SGA was 0.54, 95% CI 0.50-0.58; and 0.51, 95% CI 0.48-0.53 for low CPR. The AUC for predicting a composite adverse neonatal outcome are: 0.60, 95% CI 0.51-0.68 for abnormal UA Doppler; and 0.54, 95% CI 0.47-0.84 for low CPR.

CONCLUSION

The CPR did not improve our ability to predict neonatal SGA or other short-term adverse outcomes.

Systematic error and cognitive bias in obstetric ultrasound

Linked Comment: Ultrasound Obstet Gynecol 2019; 53: 454-464.