Comparing the relation between ultrasound-estimated fetal weight and birthweight in cohort of small-for-gestational-age fetuses

Pre-delivery BMI and the Accuracy of Fetal Weight Estimation in Very Preterm Infants

OBJECTIVES

To examine the relation between maternal pre-delivery BMI and the accuracy of sonographic estimated fetal weight (EFW) in very preterm infants (<32 weeks gestation).

METHODS

This retrospective study included singleton infants born between January 2010 and March 2023, at gestational ages 230 to 316 weeks, at a tertiary university-affiliated hospital. Absolute weight, percentage error, absolute percentage error, and overestimation and underestimation of EFW were compared between women with pre-delivery normal weight (BMI 18.5-24.99 kg/m2), overweight (BMI 25.0-29.99 kg/m2), and obesity (BMI >35.0 kg/m2). Multivariate linear regression analyses adjusted for potential confounders were performed to assess relations of maternal pre-conception and of pre-delivery BMI, with EFW accuracy.

RESULTS

Included were 286 pregnancies. The absolute difference, percentage error, absolute percentage error, error within the 10% range, and underestimation or overestimation of EFW were similar between the groups. The multivariate linear regression analyses did not show significant associations of pre-conceptional BMI or of pre-delivery BMI with the percentage error. However, for small for gestational age compared to appropriate for gestational age fetuses, the percentage error was greater (8.9% vs. -0.6%, β = 0.35, P < 0.001) and the absolute percentage error was greater (11.0% vs. 6.7%, P < 0.001). Small for gestational age fetuses were at risk of fetal weight overestimation (percentage error exceeding 15%); OR 7.20 (95% CI 2.91-17.80).

CONCLUSIONS

Maternal pre-delivery BMI was not found to be related to EFW accuracy in very preterm infants. Nevertheless, EFW should be interpreted carefully, as it may underdiagnose poor fetal growth in this population.

Predicting the fetal weight by ultrasonography for isolated polyhydramnios: Comparison of 14 formulas

OBJECTIVE

To recalculate the estimated fetal weight (EFW) based on ultrasound measurements in patients complicated with isolated polyhydramnios, using 14 current formulas to observe which formula better predicts the EFW.

METHODS

This study examined pregnant women who gave birth in the hospital between January 2015 and January 2020. Maximum vertical pocket (MVP) was classified as, mild, moderate, and severe polyhydramnios, and the patients' measurements were reanalyzed using 14 formulas. The estimation of birth weight (EBW) alongside observed birth weight (OBW) facilitated the computation of statistical indices, namely the mean absolute percentage error (MAPE) expressed as [(EBW - OBW)/OBW × 100], the mean percentage error (MPE) denoted as (EBW - OBW)/(OBW × 100), and their corresponding 95% confidence intervals.

RESULTS

A total of 564 polyhydramnios patients were included in the study. When looking at the MAPE, the lowest rate (7.65) was found in the Hadlock 2 formula. Hadlock 1, Hadlock 3, and Shinozuka formulas demonstrated MAPE values most closely aligned with Hadlock 2. Weiner I and Thurnau were the formulas with the highest MAPE values. When the cut-off values for MAPE were taken as 10%, 4/14 of the formulas (Weiner I-II, Vintzleos and Thurnau) gave results above 10%. Among 14 formulas, 3 (21.4%) had positive (sonographic overestimation) (Hadlock 3, Shinozuka, and Vintzleos) and the other 11 (78.6%) had negative MPE (sonographic underestimation).

CONCLUSION

The Hadlock 2 formula had the lowest MAPE in predicting birth weight in patients with polyhydramnios, closely followed by the Hadlock 1, Hadlock 3, and Shinozuka formulas.

Respiratory morbidity among offspring misclassified as growth restricted

OBJECTIVE

An ultrasound-based diagnosis implies that some fetuses suspected to be growth-restricted (FGR) are discovered at birth to be appropriately grown (appropriate for gestational age [AGA] birth weight, between the 10th and 90th percentile). These fetuses may thus be exposed to unnecessary medical interventions, including early labor induction. In this study, we have evaluated the long-term respiratory health of offspring misclassified as FGR.

STUDY DESIGN

A population-based cohort analysis was conducted, including deliveries of AGA singletons between 1991 and 2021 at a tertiary referral hospital. Incidence of morbidity due to various respiratory conditions was compared between AGA offspring with prenatal diagnosis of FGR, and those without a false diagnosis of FGR. The Kaplan-Meier approach was used to estimate cumulative morbidity incidence. The stratified Cox proportional-hazards model was used to control for confounders.

RESULTS

A total of 324,620 deliveries of AGA newborns were included in the analyses; 3249 of them (1.0%) were misclassified prenatally as FGR. The FGR subgroup delivered at an earlier gestational age (36.7 vs. 39.1 weeks, p < .001) and had more than 25% higher incidence of respiratory-related morbidity during childhood (33.2% vs. 26.5%), specifically related to asthma and obstructive sleep apnea (p < .001 for all). A higher cumulative morbidity rate due to respiratory conditions was observed in the Kaplan-Meier survival curve (log-rank p value < .001). This association between FGR and respiratory morbidity was independent of preterm delivery, maternal age, cesarean delivery, and child's birth year (adjusted hazard ratio = 1.14, 95% confidence interval: 1.07-1.21, p < .001), using a Cox proportional hazards model.

CONCLUSION

AGA newborns misclassified as FGR, are at an increased risk for long-term respiratory morbidity during childhood and adolescence.

Comparing Fetal Ultrasound Biometric Measurements to Neonatal Anthropometry at the Extremes of Birthweight

OBJECTIVE

 Error in birthweight prediction by sonographic estimated fetal weight (EFW) has clinical implications, such as avoidable cesarean or misclassification of fetal risk in labor. We aimed to evaluate optimal timing of ultrasound and which fetal measurements contribute to error in fetal ultrasound estimations of birth size at the extremes of birthweight.

STUDY DESIGN

 We compared differences in head circumference (HC), abdominal circumference (AC), femur length, and EFW between ultrasound and corresponding birth measurements within 14 (n = 1,290) and 7 (n = 617) days of birth for small- (SGA, <10th percentile), appropriate- (AGA, 10th-90th), and large-for-gestational age (LGA, >90th) newborns.

RESULTS

 Average differences between EFW and birthweight for SGA neonates were: -40.2 g (confidence interval [CI]: -82.1, 1.6) at 14 days versus 13.6 g (CI: -52.4, 79.7) at 7 days; for AGA, -122.4 g (-139.6, -105.1) at 14 days versus -27.2 g (-50.4, -4.0) at 7 days; and for LGA, -242.8 g (-306.5, -179.1) at 14 days versus -72.1 g (-152.0, 7.9) at 7 days. Differences between fetal and neonatal HC were larger at 14 versus 7 days, and similar to patterns for EFW and birthweight, differences were the largest for LGA at both intervals. In contrast, differences between fetal and neonatal AC were larger at 7 versus 14 days, suggesting larger error in AC estimation closer to birth.

CONCLUSION

 Using a standardized ultrasound protocol, SGA neonates had ultrasound measurements closer to actual birth measurements compared with AGA or LGA neonates. LGA neonates had the largest differences between fetal and neonatal size, with measurements 14 days from delivery showing 3- to 4-fold greater differences from birthweight. Differences in EFW and birthweight may not be explained by a single fetal measurement; whether estimation may be improved by incorporation of other knowable factors should be evaluated in future research.

KEY POINTS

· Ultrasound measurements may be inadequate to predict neonatal size at birth.. · Birthweight estimation error is higher for neonates >90th percentile.. · There is higher error in AC closer to birth..

Intrauterine Growth Restriction-Prediction and Peripartum Data on Hospital Care

Background and Objectives: We aimed to prospectively obtain data on pregnancies complicated with intrauterine growth restriction (IUGR) in the Prenatal Diagnosis Unit of the Emergency County Hospital of Craiova. We collected the demographic data of mothers, the prenatal ultrasound (US) features, the intrapartum data, and the immediate postnatal data of newborns. We aimed to assess the detection rates of IUGR fetuses (the performance of the US in estimating the actual neonatal birth weight), to describe the prenatal care pattern in our unit, and to establish predictors for the number of total hospitalization days needed postnatally. Materials and Methods: Data were collected from cases diagnosed with IUGR undergoing prenatal care in our hospital. We compared the percentile of estimated fetal weight (EFW) using the Hadlock 4 technique with the percentile of weight at birth. We retrospectively performed a regression analysis to correlate the variables predicting the number of hospitalization days. Results: Data on 111 women were processed during the period of 1 September 2019-1 September 2022. We confirmed the significant differences in US features between early- (Eo) and late-onset (Lo) IUGR cases. The detection rates were higher if the EFW was lower, and Eo-IUGR was associated with a higher number of US scans. We obtained a mathematical formula for estimating the total number of hospitalization days needed postnatally. Conclusion: Early- and late-onset IUGR have different US features prenatally and different postnatal outcomes. If the US EFW percentile is lower, a prenatal diagnosis is more likely to be made, and a closer follow-up is offered in our hospital. The total number of hospitalization days may be predicted using intrapartum and immediate postnatal data in both groups, having the potential to optimize the final financial costs and to organize the neonatal department efficiently.

The accuracy of international and national fetal growth charts in detecting small-for-gestational-age infants using the Lambda-Mu-Sigma method

Objective

To construct a national fetal growth chart using retrospective data and compared its diagnostic accuracy in predicting SGA at birth with existing international growth charts.

Method

This is a retrospective study where datasets from May 2011 to Apr 2020 were extracted to construct the fetal growth chart using the Lambda-Mu-Sigma method. SGA is defined as birth weight <10th centile. The local growth chart's diagnostic accuracy in detecting SGA at birth was evaluated using datasets from May 2020 to Apr 2021 and was compared with the WHO, Hadlock, and INTERGROWTH-21st charts. Balanced accuracy, sensitivity, and specificity were reported.

Results

A total of 68,897 scans were collected and five biometric growth charts were constructed. Our national growth chart achieved an accuracy of 69% and a sensitivity of 42% in identifying SGA at birth. The WHO chart showed similar diagnostic performance as our national growth chart, followed by the Hadlock (67% accuracy and 38% sensitivity) and INTERGROWTH-21st (57% accuracy and 19% sensitivity). The specificities for all charts were 95-96%. All growth charts showed higher accuracy in the third trimester, with an improvement of 8-16%, as compared to that in the second trimester.

Conclusion

Using the Hadlock and INTERGROWTH-21st chart in the Malaysian population may results in misdiagnose of SGA. Our population local chart has slightly higher accuracy in predicting preterm SGA in the second trimester which can enable earlier intervention for babies who are detected as SGA. All growth charts' diagnostic accuracies were poor in the second trimester, suggesting the need of improvising alternative techniques for early detection of SGA to improve fetus outcomes.

Characteristics associated with antenatally unidentified small-for-gestational-age fetuses: prospective cohort study nested within DESiGN randomized controlled trial

OBJECTIVE

To identify the clinical characteristics and patterns of ultrasound use amongst pregnancies with an antenatally unidentified small-for-gestational-age (SGA) fetus, compared with those in which SGA is identified, to understand how to design interventions that improve antenatal SGA identification.

METHODS

This was a prospective cohort study of singleton, non-anomalous SGA (birth weight < 10th centile) neonates born after 24 + 0 gestational weeks at 13 UK sites, recruited for the baseline period and control arm of the DESiGN trial. Pregnancy with antenatally unidentified SGA was defined if there was no scan or if the final scan showed estimated fetal weight (EFW) at the 10th centile or above. Identified SGA was defined if EFW was below the 10th centile at the last scan. Maternal and fetal sociodemographic and clinical characteristics were studied for associations with unidentified SGA using unadjusted and adjusted logistic regression models. Ultrasound parameters (gestational age at first growth scan, number and frequency of ultrasound scans) were described, stratified by presence of indication for serial ultrasound. Associations of unidentified SGA with absolute centile and percentage weight difference between the last scan and birth were also studied on unadjusted and adjusted logistic regression, according to time between the last scan and birth.

RESULTS

Of the 15 784 SGA babies included, SGA was not identified antenatally in 78.7% of cases. Of pregnancies with unidentified SGA, 47.1% had no recorded growth scan. Amongst 9410 pregnancies with complete data on key maternal comorbidities and antenatal complications, the risk of unidentified SGA was lower for women with any indication for serial scans (adjusted odds ratio (aOR), 0.56 (95% CI, 0.49-0.64)), for Asian compared with white women (aOR, 0.80 (95% CI, 0.69-0.93)) and for those with non-cephalic presentation at birth (aOR, 0.58 (95% CI, 0.46-0.73)). The risk of unidentified SGA was highest among women with a body mass index (BMI) of 25.0-29.9 kg/m2 (aOR, 1.15 (95% CI, 1.01-1.32)) and lowest in those with underweight BMI (aOR, 0.61 (95% CI, 0.48-0.76)) compared to women with BMI of 18.5-24.9 kg/m2 . Compared to women with identified SGA, those with unidentified SGA had fetuses of higher SGA birth-weight centile (adjusted odds for unidentified SGA increased by 1.21 (95% CI, 1.18-1.23) per one-centile increase between the 0th and 10th centiles). Duration between the last scan and birth increased with advancing gestation in pregnancies with unidentified SGA. SGA babies born within a week of the last growth scan had a mean difference between EFW and birth-weight centiles of 19.5 (SD, 13.8) centiles for the unidentified-SGA group and 0.2 (SD, 3.3) centiles for the identified-SGA group (adjusted mean difference between groups, 19.0 (95% CI, 17.8-20.1) centiles).

CONCLUSIONS

Unidentified SGA was more common amongst women without an indication for serial ultrasound, and in those with cephalic presentation at birth, BMI of 25.0-29.9 kg/m2 and less severe SGA. Ultrasound EFW was overestimated in women with unidentified SGA. This demonstrates the importance of improving the accuracy of SGA screening strategies in low-risk populations and continuing performance of ultrasound scans for term pregnancies. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Impact of maternal body mass index on the accuracy of third trimester sonographic estimation of fetal weight

OBJECTIVES

To Determine whether maternal body mass index (BMI) can affect the accuracy of sonographic estimation of fetal weight (EFW) in the third trimester when compared to neonatal birthweight (BW).

METHODS

Secondary analysis from our original prospective cohort of pregnant women beyond 34 weeks, distributed in 4 groups according to their BMI: normal, overweight, obese and morbid obese. Fetal biometry and fluid measurements were obtained by two experienced sonographers, blinded for patient's clinical information and to each other's measurements. Average EFW and neonatal BW were converted into gestational-specific Z-scores. Interobserver correlation coefficient (ICC) and Cronbach's reliability coefficient (CRC) were calculated. Bland-Altman (BA) plots were constructed to assess the level of accuracy.

RESULTS

100 women were enrolled (800 measurements obtained by 17 sonographers): 17 had normal BMI (17%), 27 were overweight (27%), 29 were obese (29%) and 27 were morbidly obese (27%). There was no statistical difference for GA at delivery (p = 0.74), EFW (p = 0.05) or BW (p = 0.09) between groups (Table 1). Mean Z-score for EFW was - 0.17 (SD 0.81) and for neonatal BW was - 0.25 (SD 0.74). ICC was 0.69 (95% CI 0.57, 0.78) and CRC was 0.82. Mean Z-score difference was small (Table 2). When stratifying according to BMI categories, the ICC ranged from 0.49 to 0.76. Reliability indices ranged from 0.66 to 0.86. The Z-scores' differences were overall small with no statistical difference (Table 3). BA showed evenly distributed interobserver differences (Fig. 1).

CONCLUSIONS

When performed by trained sonographers, fetal weight estimation in the third trimester is accurate when compared to neonatal birthweight at increasing BMI categories.

Relationship Between Maternal Serum Cortisol and Maternal Insulin Resistance and Fetal Ultrasound Characteristics in Gestational Diabetes Mellitus

INTRODUCTION

Cortisol is proven to play a crucial role in hyperglycemia and fetal development in gestational diabetes mellitus (GDM). This research aims to investigate the relationship between maternal serum cortisol and insulin resistance indices and fetal ultrasound characteristics in women with GDM.

METHODS

A cross-sectional and descriptive study on 144 GDM in Vietnam from January 2015 to December 2020. Serum cortisol was measured using electrochemiluminescence immunoassay at 8 a.m. on the examination day in the vicinity of the 24th gestational week. Fetal ultrasound was performed by an experienced person who was blind to the study.

RESULTS

The mean cortisol level in the GDM group was 627.04 nmol/L. Serum cortisol levels positively correlated with abdominal circumference (AC), fasting plasma glucose (FPG), insulin, triglycerides, HOMA2-IR, and Mathew indices (with r of 0.18, 0.22, 0.18, 0.17, 0.18, and 0.22, respectively). Serum cortisol levels negatively correlated with QUICKI and McAuley indices (with r of -0.19 and -0.21), respectively. In a univariate linear regression, maternal serum cortisol positively correlated with fetal AC, head circumference (HC), and biparietal diameter (BPD) (with r of 0.21; 0.23; and 0.25, respectively). In a multivariate linear regression analysis, cortisol positively correlated with fetal AC, HC, and BPD after adjusting to maternal McAuley index.

CONCLUSION

Serum cortisol levels in GDM correlated with fasting blood glucose, triglycerides, and insulin resistance. Besides, serum cortisol levels in GDM positively correlated with fetal development.

Reduced fetal growth velocity and weight loss are associated with adverse perinatal outcome in fetuses at risk of growth restriction

BACKGROUND

Although fetal size is associated with adverse perinatal outcome, the relationship between fetal growth velocity and adverse perinatal outcome is unclear.

OBJECTIVE

This study aimed to evaluate the relationship between fetal growth velocity and signs of cerebral blood flow redistribution, and their association with birthweight and adverse perinatal outcome.

STUDY DESIGN

This study was a secondary analysis of the TRUFFLE-2 multicenter observational prospective feasibility study of fetuses at risk of fetal growth restriction between 32⁺⁰ and 36⁺⁶ weeks of gestation (n=856), evaluated by ultrasound biometry and umbilical and middle cerebral artery Doppler. Individual fetal growth velocity was calculated from the difference of birthweight and estimated fetal weight at 3, 2, and 1 week before delivery, and by linear regression of all available estimated fetal weight measurements. Fetal estimated weight and birthweight were expressed as absolute value and as multiple of the median for statistical calculation. The coefficients of the individual linear regression of estimated fetal weight measurements (growth velocity; g/wk) were plotted against the last umbilical-cerebral ratio with subclassification for perinatal outcome. The association of these measurements with adverse perinatal outcome was assessed. The adverse perinatal outcome was a composite of abnormal condition at birth or major neonatal morbidity.

RESULTS

Adverse perinatal outcome was more frequent among fetuses whose antenatal growth was <100 g/wk, irrespective of signs of cerebral blood flow redistribution. Infants with birthweight <0.65 multiple of the median were enrolled earlier, had the lowest fetal growth velocity, higher umbilical-cerebral ratio, and were more likely to have adverse perinatal outcome. A decreasing fetal growth velocity was observed in 163 (19%) women in whom the estimated fetal weight multiple of the median regression coefficient was <-0.025, and who had higher umbilical-cerebral ratio values and more frequent adverse perinatal outcome; 67 (41%; 8% of total group) of these women had negative growth velocity. Estimated fetal weight and umbilical-cerebral ratio at admission and fetal growth velocity combined by logistic regression had a higher association with adverse perinatal outcome than any of those parameters separately (relative risk, 3.3; 95% confidence interval, 2.3-4.8).

CONCLUSION

In fetuses at risk of late preterm fetal growth restriction, reduced growth velocity is associated with an increased risk of adverse perinatal outcome, irrespective of signs of cerebral blood flow redistribution. Some fetuses showed negative growth velocity, suggesting catabolic metabolism.

Risk scores for predicting small for gestational age infants in Japan: The TMM birthree cohort study

This study aimed to construct a prediction model for small-for-gestational-age (SGA) infants in Japan by creating a risk score during pregnancy. A total of 17,073 subjects were included in the Tohoku Medical Megabank Project Birth and Three-Generation Cohort Study, a prospective cohort study. A multiple logistic regression model was used to construct risk scores during early and mid-gestational periods (11–17 and 18–21 weeks of gestation, respectively). The risk score during early gestation comprised the maternal age, height, body mass index (BMI) during early gestation, parity, assisted reproductive technology (ART) with frozen-thawed embryo transfer (FET), smoking status, blood pressure (BP) during early gestation, and maternal birth weight. The risk score during mid-gestation also consisted of the maternal age, height, BMI during mid-gestation, weight gain, parity, ART with FET, smoking status, BP level during mid-gestation, maternal birth weight, and estimated fetal weight during mid-gestation. The C-statistics of the risk scores during early- and mid-gestation were 0.658 (95% confidence interval [CI]: 0.642–0.675) and 0.725 (95% CI: 0.710–0.740), respectively. In conclusion, the predictive ability of the risk scores during mid-gestation for SGA infants was acceptable and better than that of the risk score during early gestation.

Maternal and fetal characteristics to predict c-section delivery: A scoring system for pregnant women

INTRODUCTION

Cesarean section is one of the most common obstetrical interventions that has been performed at an increasing rate globally, due to both medical and non-medical reasons. This study aims to develop a prediction tool for pregnant women potentially needing c-section, such that necessary preparations from the mothers, families, and health providers can be made.

METHODS

A total of 603 pregnant women were recruited in the first phase of c-section prediction tool development. The association between the maternal and fetal factors on the risk of c-section were analyzed, followed by a stepwise multivariate regression analysis. In the next phase, 61 pregnant women were enrolled for external validation. Discrimination was assessed using area under the curve. The calibration plot was then made and assessed using the Hosmer-Lemeshow test.

RESULTS

There were 251 (41.6%) cases of vaginal delivery and 352 (58.4%) of c-section assessed. Multivariate analysis showed that gestational age < 37 wg (OR: 1.66, 95% CI: 1.10-2.51), pre-pregnancy body mass index (underweight) (OR: 0.40, 95% CI: 0.22-0.76), no history of vaginal delivery (OR: 2.66, 95% CI: 1.76-4.02), history of uterine surgery (OR: 8.34, 95% CI: 4.54-15.30), obstetrical complications (OR: 5.61, 95% CI: 3.53-8.90), birthweight ⩾ 3500 g (OR: 4.28, 95% CI: 2.16-8.47), and non-cephalic presentation (OR: 2.74, 95% CI: 1.53-4.89) were independently associated with c-section delivery. Those parameters were included in a 7-item scoring tool, with consecutive predictive scores of 1,-1,2,3,3,2,2,1. The area under the curve result was 0.813 (95% CI: 0.779-0.847), indicating a good predictive ability. The external validation showed AUC: 0.806, 95% CI: 0.694-0.917, Hosmer-Lemeshow test p = 0.666 and calibration plot coefficient of r = 0.939.

CONCLUSION

A total of 7 maternal-fetal factors were found to be strongly associated with c-section delivery, including gestational age < 37, maternal underweight body mass index, previous uterine surgery, obstetrical complications, birthweight ⩾ 3500, history of vaginal delivery, and non-cephalic presentation. Using these factors, a prediction tool was developed and validated with good quality.

Fetal weight change close to term is proportional to the birthweight percentile

OBJECTIVE

To investigate the relationship between the difference in estimated fetal weight and birthweight at or close to term, and in relation to Doppler parameters.

STUDY DESIGN

A cohort study of all term singleton pregnancies who underwent an ultrasound within two weeks of delivery after 36 weeks at one institution in one calendar year. When available, Doppler measurements of umbilical and middle cerebral artery pulsatility index were recorded. Data were analysed by Pearson rank correlation.

RESULTS

Of 8517 eligible deliveries, 885 women had an ultrasound scan within 2 weeks of delivery. Mean daily differences between estimated fetal weight and birth weight were: those born <10th percentile lost 26 g per day (95 % CI -36 to -16), 10-50th percentile gained 7 g per day (95 % CI -2 to 15), 50th-90th percentile gained 27 g per day (95 % CI 19-35) and >90th percentile gained 48 g per day (95 % CI 32-64). There was a negative correlation between umbilical: middle cerebral artery pulsatility index and the change in weight per day (n = 348, p = 0.001, r = 0.17).

CONCLUSIONS

Difference in the estimated fetal weight and birthweight, expressed as grams growth per day, is proportional to the birthweight percentile. Fetuses with a birthweight >10th percentile gain weight, while those with a birthweight <10th percentile apparently decline in weight between their final ultrasound estimated fetal weight and delivery. In babies with the smallest or apparent negative weight gain there was an association with Doppler parameters that signified hypoxia indicating fetal growth at term may be restricted by impaired placental function. Estimated fetal weight may be a poor predictor of birthweight for reasons other than ultrasound or algorithmic error.