New fetal weight estimation models using fractional limb volume

Origins of obesity in the womb: Fetal adiposity and its determinants

Birth weight is an important predictor of perinatal complications and long-term health outcomes of offspring. Fetal programming influenced by maternal obesity, overnutrition, and hyperglycemia has been proposed as the fuel overload hypothesis. Recent investigations related with fetal body composition have revealed that neonatal adiposity can be predicted by fetal fat mass, and that maternal insulin resistance and serum leptin level are indicators of fetal adiposity. Based on the current evidence, the origins of obesity can partly be traced back into the fetal life. Further clarification of the determinants of fetal fat mass may lead to the clinical interventions and treatment strategies for fetal growth and development. This effort potentially leads to the elucidation of pathological conditions related with long-term health outcomes and the primary prevention of childhood obesity and early onset metabolic syndrome.

Prediction of large-for-gestational age at 36 weeks' gestation: two-dimensional ultrasound vs three-dimensional ultrasound vs magnetic resonance imaging

OBJECTIVE

To compare the performance of two-dimensional ultrasound (2D-US), three-dimensional ultrasound (3D-US) and magnetic resonance imaging (MRI) at 36 weeks' gestation in predicting the delivery of a large-for-gestational-age (LGA) neonate, defined as birth weight ≥ 95th percentile, in patients at high and low risk for macrosomia.

METHODS

This was a secondary analysis of a prospective observational study conducted between January 2017 and February 2019. Women with a singleton pregnancy at 36 weeks' gestation underwent 2D-US, 3D-US and MRI within 15 min for estimation of fetal weight. Weight estimations and birth weight were plotted on a growth curve to obtain percentiles for comparison. Participants were considered high risk if they had at least one of the following risk factors: diabetes mellitus, estimated fetal weight ≥ 90th percentile at the routine third-trimester ultrasound examination, obesity (prepregnancy body mass index ≥ 30 kg/m2) or excessive weight gain during pregnancy. The outcome was the diagnostic performance of each modality in the prediction of birth weight ≥ 95th percentile, expressed as the area under the receiver-operating-characteristics curve (AUC), sensitivity, specificity and positive and negative predictive values.

RESULTS

A total of 965 women were included, of whom 533 (55.23%) were high risk and 432 (44.77%) were low risk. In the low-risk group, the AUCs for birth weight ≥ 95th percentile were 0.982 for MRI, 0.964 for 2D-US and 0.962 for 3D-US; pairwise comparisons were non-significant. In the high-risk group, the AUCs were 0.959 for MRI, 0.909 for 2D-US and 0.894 for 3D-US. A statistically significant difference was noted between MRI and both 2D-US (P = 0.002) and 3D-US (P = 0.002), but not between 2D-US and 3D-US (P = 0.503). In the high-risk group, MRI had the highest sensitivity (65.79%) compared with 2D-US (36.84%, P = 0.002) and 3D-US (21.05%, P < 0.001), whereas 3D-US had the highest specificity (98.99%) compared with 2D-US (96.77%, P = 0.005) and MRI (96.97%, P = 0.004).

CONCLUSIONS

At 36 weeks' gestation, MRI has better performance compared with 2D-US and 3D-US in predicting birth weight ≥ 95th percentile in patients at high risk for macrosomia, whereas the performance of 2D-US and 3D-US is comparable. For low-risk patients, the three modalities perform similarly. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Association of maternal obesity with growth of fetal fractional limb volume

BACKGROUND

Maternal obesity influences birth weight and newborn adiposity. Fetal fractional limb volume has recently been introduced as a useful parameter for the proxy of fetal adiposity. However, the association between maternal adiposity and the growth of fetal fractional limb volume has not been examined.

AIMS

To investigate the association of maternal pre-pregnancy BMI with the growth of fetal fractional limb volume.

STUDY DESIGN

Prospective cohort study.

SUBJECTS

Women with singleton uncomplicated pregnancies enrolled between July 2017 and June 2020.

OUTCOME MEASURES

Fetal fractional limb volume was assessed between 20 and 40 weeks' gestation, measured as cylindrical limb volume based on 50 % of the total diaphysis length. The measured fractional limb volume at each gestational week were converted to z-scores based on a previous report. The association between pre-pregnancy BMI and fetal fractional limb volume was examined. Maternal age, parity, gestational weight gain and fetal sex were considered as potential confounding variables.

RESULTS

Ultrasound scans of 455 fractional arm volume and thigh volume were obtained. Fractional limb volume increased linearly until the second trimester of gestation, then increased exponentially in the third trimester. Maternal pre-pregnancy BMI was significantly correlated with z-scores of fractional arm volume and thigh volume across gestation. The post-hoc analysis showed the association between pre-pregnancy BMI and fractional arm volume was significant especially between 34 and 40 weeks.

CONCLUSIONS

Maternal obesity influences the growth pattern of fetal fractional limb volume. Fractional arm volume may potentially provide a useful surrogate marker of fetal nutritional status in late gestation.

Establishing Chinese Fetal Growth Standards: Why and How

Choosing a fetal growth standard or reference is crucial when defining normal and abnormal fetal growth. We reviewed the recently published standards and compared them with a customized fetal growth chart based on a nationwide population in China. There were substantial discrepancies in the fetal growth pattern, suggesting that these standards may not be applicable to Chinese fetuses. Developing a Chinese-specific standard may better meet our clinical requirements. We also discuss the steps to establish a Chinese fetal growth standard and the potential challenges, including regional disparities and accuracy of sonographic estimated fetal weight. Standardized ultrasound measurement protocol and the introduction of new ultrasonography technology may be helpful in developing a more precise standard than existing ones for the Chinese population.

Semiautomatic Assessment of Fetal Fractional Limb Volume for Weight Prediction in Clinical Praxis: How Does It Perform in Routine Use?

OBJECTIVES

Semiautomatic fractional limb volume (FLV) models have recently produced promising results for fetal birth weight (BW) estimation. We tested those models in a more unselected population hypothesizing that the FLV models would improve accuracy and precision of fetal BW estimation compared to the Hadlock model.

METHODS

We compared the performance of different BW prediction models: Hadlock (biparietal diameter [BPD], abdominal circumference (AC), femur diaphysis length) and modified Lee thigh volume (TVol) and arm volume (AVol) (BPD, AC, automated fractional TVol, and AVol). Accuracy (systematic errors, mean percent differences) and precision (random errors, ± 1 SD of percent differences) were calculated.

RESULTS

A total of 75 fetuses were included for final analysis. The Hadlock model showed the most consistent results with accurate BW estimation not significantly different from zero (-0.37 ± 8.53%). The modified fractional thigh and arm volume models were less accurate but trended toward more precise results (-2.63 ± 7.69% and -3.85 ± 7.47%, respectively). In addition, the modified TVol model showed the trend to predict more BWs within ±10% of the actual BW compared to the Hadlock model (81.3 versus 74.67%, ns).

CONCLUSIONS

Based on our results, fetal weight estimation using the modified semiautomatic FLV models generates less accurate results in third-trimester fetuses compared to the Hadlock model. Those models recently published might improve the results of BW prediction by showing a higher precision than conventional models, especially in small and large fetuses. Further studies are needed to investigate the clinical usefulness of the new models.

Birth weight prediction by Lee formula based on fractional thigh volume in term pregnancies - is it helpful?

INTRODUCTION

Ultrasonographic estimation of fetal weight (EFW) is a standard obstetrical procedure in daily clinical practice. Formulas for calculating EFW most commonly are a combination of two-dimensional measurements. A relatively new approach is the use of three-dimensional measurements such as fractional thigh volume (TVol) incorporated into specific regression equations. The objective of this study was to compare the Lee formula based on three-dimensional ultrasonographic TVol in the estimation of fetal weight before delivery in term pregnancies to the Hadlock I formula.

MATERIAL AND METHODS

2D/3D abdominal ultrasonography was performed in 104 women, 37-41 gestational weeks, and measurements of biparietal diameter, head circumference, abdomen circumference, and femur length, TVol were taken. Using these measurements, we compared the Lee to the Hadlock formulas in EFW. The timing of procedures was measured in 20 randomly chosen patients by an independent observer.

RESULTS

Mean percentage errors of formulas, Lee vs. Hadlock, were 2.13 ±9.31% vs. -2.02 ±8.79%, (p = 0.001). There was no statistically significant difference in median absolute percentage errors between the two formulas (6.09% vs. 6.10%, p = 0.56). The proportion of newborns with estimated birth weights (BW) within ±10% of actual BW was not significantly different between the two formulas (73% vs. 71%, p = 0.11). There was a significant difference in the proportion of the newborns with estimated BW within ±5% (33% vs. 42%, p = 0.000006). Statistical measurements for test performance in detecting fetuses with BW ≥ 4000 g were sensitivity 85% vs. 60%, specificity 88% vs. 96%, and accuracy 88% vs. 89%. There was no significant difference in the time to perform the measurements (69 s for Lee formula vs. 58 s for Hadlock formula, p = 0.16).

CONCLUSIONS

Thigh volume measurement incorporated into the Lee single parameter formula is comparable to the Hadlock I formula in terms of accuracy in predicting fetal weight before delivery. There was no significant difference in the time needed for taking necessary measurements between the two groups.

Accuracy of Ultrasound to Predict Neonatal Birth Weight Among Fetuses With Gastroschisis: Impact on Timing of Delivery

OBJECTIVES

To determine the accuracy of ultrasound estimation of fetal weight among fetuses with gastroschisis and how the diagnosis of fetal growth restriction (FGR) affects the timing of delivery.

METHODS

This was a retrospective cohort study including all fetuses with a diagnosis of gastroschisis at our institution from November 2012 through October 2017. We excluded multiple gestations, pregnancies with major structural or chromosomal abnormalities, and those for which prenatal and postnatal follow-up were unavailable. Performance characteristics of ultrasound to predict being small for gestational age (SGA) were calculated for the first and last ultrasound estimations of fetal weight.

RESULTS

Our cohort included 75 cases of gastroschisis. At the initial ultrasound estimation, 15 of 58 (25.9%) fetuses met criteria for FGR; 48 of 70 (68.6%) met criteria at the time of the last ultrasound estimation (median, 34.7 weeks). Cesarean delivery was performed for 37 of 75 (49.3%), with FGR and concern for fetal distress as the indication for delivery in 17 of 37 (45.9%). Only 6 of 17 (35.3%) of the neonates born by cesarean delivery for an indication of FGR and fetal distress were SGA. The initial ultrasound designation of FGR corresponded to SGA at birth in 8 of 15 (53.3%), whereas the last ultrasound estimation corresponded to SGA in 17 of 48 (35.4%). The initial ultrasound estimation agreed with the last ultrasound estimation before delivery with the diagnosis of FGR in 13 of 15 (86.7%).

CONCLUSIONS

Ultrasound in the third trimester was sensitive but had a low positive predictive value and low accuracy for the diagnosis of SGA at birth for fetuses with gastroschisis. A large proportion of fetuses were born by cesarean delivery with indications related to FGR or fetal concerns.

Soft tissue assessment for fetal growth restriction

Contemporary clinical practice heavily relies on interpretation of population-based birth weight standards to evaluate neonatal nutrition status. Obstetricians have adopted the use of estimated fetal weight in a similar manner to estimate fetal nutritional status. However, most fetal weight prediction models overemphasize skeletal parameters such as biparietal diameter, head circumference, and femur diaphysis length. Although most EFW calculations also include abdominal circumference, this 2D growth parameter is largely defined by liver size and a small rim of subcutaneous fat. Advances in 3D ultrasound imaging and the development of more robust image analysis tools have now made it possible to reliably add a soft tissue component for fetal nutritional assessment. This chapter explains why fetal soft tissue evaluation is clinically relevant, describes different techniques for evaluating these sonographic parameters, and outlines future directions for their practical utility in the care of malnourished fetuses.

Fetal weight estimation by automated three-dimensional limb volume model in late third trimester compared to two-dimensional model: a cross-sectional prospective observational study

Background

Accurate estimation of fetal weight is important for prenatal care and for detection of fetal growth abnormalities. Prediction of fetal weight entails the indirect measurement of fetal biometry by ultrasound that is then introduced into formulae to calculate the estimated fetal weight. The aim of our study was to evaluate the accuracy of fetal weight estimation of Chinese fetuses in the third trimester using an automated three-dimensional (3D) fractional limb volume model, and to compare this model with the traditional two-dimensional (2D) model.

Methods

Prospective 2D and 3D ultrasonography were performed among women with singleton pregnancies 7 days before delivery to obtain 2D data, including fetal biparietal diameter, abdominal circumference and femur length, as well as 3D data, including the fractional arm volume (AVol) and fractional thigh volume (TVol). The fetal weight was estimated using the 2D model and the 3D fractional limb volume model respectively. Percentage error was defined as (estimated fetal weight - actual birth weight) divided by actual birth weight and multiplied by 100. Systematic errors (accuracy) were evaluated as the mean percentage error (MPE). Random errors (precision) were calculated as ±1 SD of percentage error. The intraclass correlation coefficient (ICC) was used to analyze the inter-observer reliability of the 3D ultrasound measurements of fractional limb volume.

Results

Ultrasound examination was performed on 56 fetuses at 39.6 ± 1.4 weeks’ gestation. The average birth weight of the newborns was 3393 ± 530 g. The average fetal weight estimated by the 2D model was 3478 ± 467 g, and the MPE was 3.2 ± 8.9. The average fetal weights estimated by AVol and TVol of the 3D model were 3268 ± 467 g and 3250 ± 485 g, respectively, and the MPEs were − 3.3 ± 6.6 and − 3.9 ± 6.1, respectively. For the 3D TVol model, the proportion of fetuses with estimated error ≤ 5% was significantly higher than that of the 2D model (55.4% vs. 33.9%, p < 0.05). For fetuses with a birth weight < 3500 g, the accuracy of the AVol and TVol models were better than the 2D model (− 0.8 vs. 7.0 and − 2.8 vs. 7.0, both p < 0.05). Moreover, for these fetuses, the proportions of estimated error ≤ 5% of the AVol and TVol models were 58.1 and 64.5%, respectively, significantly higher than that of the 2D model (19.4%) (both p < 0.05). The inter-observer reliability of measuring fetal AVol and TVol were high, with the ICCs of 0.921 and 0.963, respectively.

Conclusion

In this cohort, the automated 3D fractional limb volume model improves the accuracy of weight estimation in most third-trimester fetuses. Prediction accuracy of the 3D model for neonatal BW, particularly < 3500 g was higher than that of the traditional 2D model.

Predicting fetal weight by three-dimensional limb volume ultrasound (AVol/TVol) and abdominal circumference

BACKGROUND

Fetal weight is an important parameter to ensure maternal and child safety. The purpose of this study was to use three-dimensional (3D) limb volume ultrasound combined with fetal abdominal circumference (AC) measurement to establish a model to predict fetal weight and evaluate its efficiency.

METHODS

A total of 211 participants with single pregnancy (28-42 weeks) were selected between September 2017 and December 2018 in the Beijing Obstetrics and Gynecology Hospital of Capital Medical University. The upper arm (AVol)/thigh volume (TVol) of fetuses was measured by the 3D limb volume technique. Fetal AC was measured by two-dimensional ultrasound. Nine cases were excluded due to incomplete information or the interval between examination and delivery >7 days. The enrolled 202 participants were divided into a model group (134 cases, 70%) and a verification group (68 cases, 30%) by mechanical sampling method. The linear relationship between limb volume and fetal weight was evaluated using Pearson Chi-squared test. The prediction model formula was established by multivariate regression with data from the model group. Accuracy of the model formula was evaluated with verification group data and compared with traditional formulas (Hadlock, Lee2009, and INTERGROWTH-21st) by paired t-test and residual analysis. Receiver operating characteristic curves were generated to predict macrosomia.

RESULTS

AC, AVol, and TVol were linearly related to fetal weight. Pearson correlation coefficient was 0.866, 0.862, and 0.910, respectively. The prediction model based on AVol/TVol and AC was established as follows: Y = -481.965 + 12.194TVol + 15.358AVol + 67.998AC, R2adj = 0.868. The scatter plot showed that when birth weight fluctuated by 5% (i.e., 95% to 105%), the difference between the predicted fetal weight by the model and the actual weight was small. A paired t-test showed that there was no significant difference between the predicted fetal weight and the actual birth weight (t = -1.015, P = 0.314). Moreover, the residual analysis showed that the model formula's prediction efficiency was better than the traditional formulas with a mean residual of 35,360.170. The combined model of AVol/TVol and AC was superior to the Lee2009 and INTERGROWTH-21st formulas in the diagnosis of macrosomia. Its predictive sensitivity and specificity were 87.5% and 91.7%, respectively.

CONCLUSION

Fetal weight prediction model established by semi-automatic 3D limb volume combined with AC is of high accuracy, sensitivity, and specificity. The prediction model formula shows higher predictive efficiency, especially for the diagnosis of macrosomia.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03002246; https://clinicaltrials.gov/ct2/show/NCT03002246?recrs=e&cond=fetal&draw=8&rank=67.

Prediction of Birth Weight and Neonatal Adiposity Using Ultrasound Assessment of Soft Tissue Parameters in Addition to Two-Dimensional Conventional Biometry

INTRODUCTION

We aim to evaluate the supplementary predictive value of soft tissue markers, including fetal limb volumes, for fetal birth weight and fat tissue weight.

METHODS

This is a prospective study of 60 patients undergoing term induction of labor. Ultrasound was performed 48 h before birth, and 2D sonographic measurements, subcutaneous tissue thickness, and 3D fetal limb volumes were taken. Birth weight and neonatal fat weight were assessed by plethysmography. Clinical data were collected. The relation between ultrasound and neonatal outcomes was assessed by univariate and multivariate predictive models. The estimated and actual birth weights were compared applying different published formulas, and systematic and random error were collected and compared.

RESULTS

3D fetal limb volumes showed a strong relation to birth weight, absolute weight, and relative fat weight. The Lee 6 formula performed better than either Hadlock 3 or Lee 3 with the lowest random error. Fractional limb volumes involve a highly reproducible technique, with excellent correlation (intra-class coefficient >0.90) for both inter- and intra-observer reliability. The prevalence of estimated EFW measures within 10% error from the actual birth weight was 71.7% with the Hadlock 3 model and 95.0% with the Lee 6 model (p = 0.09).

CONCLUSION

Late assessment of 3D fetal limb volume in upper and lower extremities is not only useful for accurately predicting birth weight but is a useful marker for prediction of birth fat tissue weight.

Use of ultrasound fetal shoulder soft tissue thickness measurement in estimation of fetal weight

AIMS

Birth weight (BW) estimation with ultrasound is of great importance in delivery decision and management of complications of delivery. The aim was to evaluate the effect of femur, humerus, and clavicular soft tissue thickness on BW and developed a formula for proper estimation of fetal weight.

METHODS

This prospective cohort study, included 231singleton pregnancies, with 34 and 42 weeks of gestation, delivered within 48 h after ultrasound examination. In addition to four biometric ultrasound measures, shoulder soft tissue thickness, thigh and arm soft tissue thickness were measured from outer margin of skin to outer margin of bone shaft by same investigator. Spearman correlation test was used to assess correlations between soft tissue thickness measurements and BW. Linear regression model was used and R² to test accuracy of the new formula.

RESULTS

The mean humerus soft tissue thickness (HSTT) was 12 ± 3.5 mm (6-23.9 mm), mean femur soft tissue thickness (FSTT) was 15.9 ± 3.8 mm (7.3-32 mm), mean clavicular soft tissue thickness (CSTT) was 12.9 ± 3.2 mm (7.3-24 mm). There was a low correlation between BW and FSTT (r = 0.21, p = 0.001) and CSTT (r = 0.18, p = 0.005). Best fit formula was Log (BW) = -5697 + 7.2 (HC) + 15.3 (AC) + 22.6 (FL) + 17 (CSTT), was significantly correlated with BW (R² = 0.60).

CONCLUSION

BW increased as the ultrasound shoulder soft tissue thickness increased. Adding soft tissue thickness measurements to fetal biometry is similar in terms of estimating fetal weight from the existing estimated fetal weight formula.

Fetal Weight Estimation Using Automated Fractional Limb Volume With 2-Dimensional Size Parameters in Diabetic Pregnancies

OBJECTIVES

To examine the effect of adding automated fetal fractional limb volume (FLV) with conventional 2-dimensional (2D) fetal weight estimation procedures in a cohort of diabetic pregnancies.

METHODS

A pilot study of diabetic pregnancies measured standard fetal biometry within 7 days of delivery. Fractional arm volume (AVol) and fractional thigh volume (TVol) soft tissue parameters were measured with a commercially available automated software utility (5D Limb Vol; Samsung Medison Co, Ltd, Seoul, Korea). Three conventional weight prediction models that included only 2D size parameters were compared to FLV models that included AVol or TVol. Estimated and actual birth weight (BW) were assessed for the mean percent difference ± standard deviation of the percent differences. Systematic errors were evaluated by the Student t test, and random errors were compared by the Pitman test for correlated variances. The proportion of neonates with estimated fetal weight within 10% of BW was compared between groups by the McNemar test.

RESULTS

Ninety gravid women were enrolled with pregestational (26.7%) or gestational (73.3%) diabetes. All prediction models were accurate, with the exception of small underestimations by the model of Schild et al (-3.8%; Ultrasound Obstet Gynecol 2004; 23:30-35). Random errors for the AVol (6.2%) and TVol (6.9%) models were significantly more precise than the other 3 prediction models: Hadlock et al (7.8%; Am J Obstet Gynecol 1985; 151:333-337), INTERGROWTH-21st (8.0%; Ultrasound Obstet Gynecol 2017; 49:478-486), and Schild et al (8.6%; P < .01). The greatest proportion of cases with BW ±10% was also classified by the AVol (91.1%) and TVol (91.1%) models, followed by Hadlock (83.3%), INTERGROWTH-21st (78.9%), and Schild (76.7%) predictions.

CONCLUSIONS

The addition of automated FLV measurements to conventional 2D biometry was associated with improved weight predictions in this cohort of diabetic pregnancies.

The Relationship between Fetal Abdominal Wall Thickness and Intrapartum Complications amongst Mothers with Pregestational Type 2 Diabetes

OBJECTIVES

To evaluate the utility of fetal abdominal wall thickness (AWT) for predicting intrapartum complications amongst mothers with pregestational type 2 diabetes.

METHODS

This was a historical cohort study of pregnant mothers with pregestational type 2 diabetes delivering at a Canadian tertiary-care center between January 1, 2014, and December 31, 2018. Delivery records were reviewed to collect information about demographics and peripartum complications. Stored fetal ultrasound images from 36 weeks' gestation were reviewed to collect fetal biometry and postprocessing measurement of AWT performed in a standardized fashion by 2 blinded and independent observers. The relationship between fetal AWT was then correlated with risk of intrapartum complications including emergency Caesarean section (CS) and shoulder dystocia.

RESULTS

216 pregnant women with type 2 diabetes had planned vaginal deliveries and were eligible for inclusion. Mean maternal age was 31.3 years, and almost all were overweight or obese at the time of delivery (96.8%). Overall, the incidence of shoulder dystocia and emergency intrapartum CS was 7.4% and 17.6%, respectively. There was no difference in mean fetal AWT between those having a spontaneous vaginal delivery (8.2 mm (95% CI 7.9-8.5)) and those needing emergency intrapartum CS (8.1 mm (95% CI 7.4-8.8); p = 0.71) or shoulder dystocia (8.7 mm (95% CI 7.9-9.5); p = 0.23). There was strong interobserver correlation of AWT measurements (r = 0.838; p < 0.00001). The strongest association with intrapartum complications was birthweight (p = 0.003): with birthweight > 4000 grams, the relative risk of shoulder dystocia or CS is 2.75 (95% CI 1.74-4.36; p < 0.001).

CONCLUSIONS

There was no obvious benefit of AWT measurement at 36 weeks for predicting shoulder dystocia or intrapartum CS amongst women with type 2 diabetes in our population. The strongest predictor of intrapartum complications remained birthweight, and so studies for improving estimation of fetal weight and evaluating the role of intrapartum ultrasound for predicting risk of delivery complications are still needed.

Fetal Weight Estimation Using Automated Fractional Limb Volume With 2-Dimensional Size Parameters: A Multicenter Study

OBJECTIVES

To develop new fetal weight prediction models using automated fractional limb volume (FLV).

METHODS

A prospective multicenter study measured fetal biometry within 4 to 7 days of delivery. Three-dimensional data acquisition included the automated FLV that was based on 50% of the humerus diaphysis (fractional arm volume [AVol]) or 50% of the femur diaphysis (fractional thigh volume [TVol]) length. A regression analysis provided population sample-specific coefficients to develop 4 weight estimation models. Estimated and actual birth weights (BWs) were compared for the mean percent difference ± standard deviation of the percent differences. Systematic errors were analyzed by the Student t test, and random errors were compared by the Pitman test.

RESULTS

A total of 328 pregnancies were scanned before delivery (BW range, 825-5470 g). Only 71.3% to 72.6% of weight estimations were within 10% of actual BW using original published models by Hadlock et al (Am J Obstet Gynecol 1985; 151:333-337) and INTERGROWTH-21st (Ultrasound Obstet Gynecol 2017; 49:478-486). All predictions were accurate by using sample-specific model coefficients to minimize bias in making these comparisons (Hadlock, 0.4% ± 8.7%; INTERGROWTH-21st, 0.5% ± 10.0%; AVol, 0.3% ± 7.4%; and TVol, 0.3% ± 8.0%). Both AVol- and TVol-based models improved the percentage of correctly classified BW ±10% in 83.2% and 83.9% of cases, respectively, compared to the INTERGROWTH-21st model (73.8%; P < .01). For BW of less than 2500 g, all models slightly overestimated BW (+2.0% to +3.1%). For BW of greater than 4000 g, AVol (-2.4% ± 6.5%) and TVol (-2.3% ± 6.9%) models) had weight predictions with small systematic errors that were not different from zero (P > .05). For these larger fetuses, both AVol and TVol models correctly classified BW (±10%) in 83.3% and 87.5% of cases compared to the others (Hadlock, 79.2%; INTERGROWTH-21st, 70.8%) although these differences did not reach statistical significance.

CONCLUSIONS

In this cohort, the inclusion of automated FLV measurements with conventional 2-dimensional biometry was generally associated with improved weight predictions.

Differences in fetal fractional limb volume changes in normal and gestational diabetic pregnancies: an exploratory observational study

OBJECTIVE

Fetal fractional limb volume has been proposed as a useful measure for quantifying fetal soft tissue development. The aim of this study was to investigate the growth of fractional arm volume (AVol) and fractional thigh volume (TVol) of fetuses with maternal gestational diabetes (GDM) compared with those of fetuses with normal glucose tolerance (NGT). We hypothesised fetal fractional limb volume would be larger in the GDM group than in the NGT group in late gestation.

DESIGN

Exploratory observational study.

SETTING

Saitama Municipal Hospital.

SAMPLE

A total of 165 (125 NGT and 40 GDM) singleton Japanese pregnant women.

METHODS

AVol and TVol were assessed between 20 and 37 weeks' gestation as cylindrical limb volumes based on 50% of the fetal humeral or femoral diaphysis length. Women were diagnosed as GDM based on the criteria of the Japan Society of Obstetrics and Gynecology.

MAIN OUTCOME MEASURES

AVol and TVol were compared between women with NGT and those with GDM at each gestational age period (2-week intervals from 20 to 37 weeks' gestation).

RESULTS

Overall, 287 ultrasound scans were performed (NGT group, 205 scans; GDM group, 82 scans). There was no significant difference of AVol between the groups before 32 weeks' gestation. AVol was significantly larger in the GDM group than in the NGT group after 32 weeks' gestation (P < 0.05). TVol was not statistically different between the groups across gestation.

CONCLUSIONS

Detection of variations in fetal AVol may provide greater insight into understanding the origins of altered fetal body proportion in GDM.

TWEETABLE ABSTRACT

AVol, but not TVol, is significantly larger in fetuses with GDM than in those with NGT after 32 weeks' gestation.

Body Composition During Pregnancy Differs by Obesity Class

OBJECTIVE

The aim of this study is to characterize changes in body composition during pregnancy in women with obesity.

METHODS

Fifty-four healthy women with obesity (class 1, 30-34.9 kg/m² : n = 25; class 2, 35-39.9 kg/m² : n = 21; class 3, ≥ 40.0 kg/m² : n = 8) expecting a singleton pregnancy were studied. Body composition was measured in early pregnancy (13-16 weeks), midpregnancy (24-27 weeks), and late pregnancy (35-37 weeks) using air displacement plethysmography, stable isotopes, and skinfold thickness measurements. Fasting glucose, insulin, and leptin were measured.

RESULTS

The gain in fat-free mass was lower in the second trimester compared with the third (2.7 ± 0.2 to 5.3 ± 0.2 kg; P < 0.001), whereas fat mass accumulation declined over time (0.6 ± 0.3 to -0.7 ± 0.4 kg; P = 0.005). Women with class 1 and 2 obesity gained 1.1 ± 0.7 kg of fat mass during pregnancy, while women with class 3 obesity lost 4.1 ± 0.6 kg (both P < 0.001). The difference in fat accumulation between obesity classes was observed only in the second trimester (P = 0.02). Gestational weight gain was associated positively with changes in plasma concentrations of insulin, leptin, and insulin resistance (all P < 0.01).

CONCLUSIONS

Gestational weight gain in pregnancy differs by obesity class and trimester. Women with class 3 obesity gain less body weight and fat mass. Fat mass gain is most likely preventable in the second trimester.

Morphometric study of the diaphragmatic surface of the liver in the human fetus

This study aimed to examine age-specific reference intervals and growth dynamics of the best fit for liver dimensions on the diaphragmatic surface of the fetal liver. The research material consisted of 69 human fetuses of both sexes (32♂, 37♀) aged 18–30 weeks. Using methods of anatomical dissection, digital image analysis and statistics, a total of 10 measurements and 2 calculations were performed. No statistical significant differences between sexes were found (p>0.05). The parameters studied displayed growth models that followed natural logarithmic functions. The mean value of the transverse–to–vertical diameter ratio of the liver throughout the analyzed period was 0.71±0.11. The isthmic ratio decreased significantly from 0.81±0.12 in the 18–19th week to 0.62±0.06 in the 26–27th week, and then increased to 0.68±0.11 in the 28–30th week of fetal life (p<0.01). The morphometric parameters of the diaphragmatic surface of the liver present age-specific reference data. No sex differences are found. The transverse–to–vertical diameter ratio supports a proportionate growth of the fetal liver. Quantitative anatomy of the growing liver may be of relevance in both the ultrasound monitoring of the fetal development and the early detection of liver anomalies.

Evaluating the accuracy and precision of sonographic fetal weight estimation models in extremely early-onset fetal growth restriction

INTRODUCTION

Birthweight is a critical predictor of survival in extremely early-onset fetal growth restriction (diagnosed pre-28 weeks' gestation, with abnormal umbilical/uterine artery Doppler waveforms), therefore accurate fetal weight estimation is a crucial component of antenatal management. Currently available sonographic fetal weight estimation models were predominantly developed in populations of mixed gestational age and varying fetal weights, but not specifically tested within the context of extremely early-onset fetal growth restriction. This study aimed to determine the accuracy and precision of fetal weight estimation in this population and investigate whether model performance is affected by other factors.

MATERIAL AND METHODS

Cases where a growth scan was performed within 48 hours of delivery (n = 65) were identified from a cohort of extremely early-onset fetal growth-restricted pregnancies at a single tertiary maternity center (n = 159). Fetal biometry measurements were used to calculate estimated fetal weight using 21 previously published models. Systematic and random errors were calculated for each model and used to identify the best performing model, which in turn was used to explore the relationship between error and gestation, estimated fetal weight, fetal presentation, fetal asymmetry and amniotic fluid volume.

RESULTS

Both systematic (median 8.2%; range -44.1 to 49.5%) and random error (median 11.6%; range 9.7-23.8%) varied widely across models. The best performing model was Hadlock head circumference-abdominal circumference-femur length (HC-AC-FL), regardless of gestational age, fetal size, fetal presentation or asymmetry, with an overall systematic error of 1.5% and random error of 9.7%. Despite this, it only calculated the estimated fetal weight within 10% of birthweight in 64.6% of cases. There was a weak negative relation between mean percentage error with Hadlock HC-AC-FL and amniotic fluid volume, suggesting fetal weight is overestimated at lower liquor volumes and underestimated at higher liquor volumes (P = 0.002, adjusted R²  = 0.08).

CONCLUSIONS

Hadlock HC-AC-FL is the most accurate model currently available to estimate fetal weight in extremely early-onset fetal growth restriction independent of gestation or fetal size, asymmetry or presentation. However, for 35.4% of cases in this study, estimated fetal weight calculated using this model deviates by more than 10% from birthweight, highlighting a need for an improved model.

Prediction of fetal macrosomia using two-dimensional and three-dimensional ultrasound

OBJECTIVE

The estimation of the fetal weight by three-dimensional (3D) ultrasound (US) with fractional thigh volume (TVol) has been suggested to be more accurate than two-dimensional (2D) US particularly within the context of fetuses at risk of macrosomia. The objective of this study was to compare the accuracy of 2D US and 3D US with two different methods of projection for the identification of fetal macrosomia at term.

STUDY DESIGN

Prospective study which included women at risk for fetal macrosomia referred for fetal biometry between 34⁺⁰-36⁺⁶ weeks. The estimated fetal weight (EFW) was computed using 2D US and the Hadlock Model IV or through 3D US and the Model VI by Lee et al. The projection of the EFW at the time of delivery was performed by using Yudkin's chart percentiles and the gestation-adjusted projection (GAP) method.

RESULTS

Overall, 230 patients were included. Paired comparison between 2D-US-EFW and 3D-US-EFW with either method of projection of the EFW at birth suggested different properties of the techniques, being 2D-US-EFW associated with higher sensitivity and 3D-US-EFW with higher specificity, PPV and LR + . At ROC curve no difference was found in the prediction of birthweight ≥90th centile using 2D-US-EFW or 3D-US-EFW (AUC 0.831, 95%CI 0.768-0.894 versus AUC 0.860, 95%CI 0.799-0.920, respectively, p 0.37) nor in the prediction of birthweight >95th centile with 2D-US-EFW compared to 3D-US-EFW (0.803, 95%CI 0.731-0.874 versus 0.866, 95%CI 0.805-0.926, respectively, p 0.07). Similarly, a non-significant difference in the accuracy of the prediction of birthweight >4000 g (AUC 0.788, 95%CI 0.716-0.859 for 2D-US-EFW vs AUC 0.802, 95%CI 0.723-0.880 for 3D-US-EFW, p 0.72) and >4500 g (0.828, 95%CI 0.720-0.936 for 2D-US-EFW vs 0.858, 95%CI 0.759-0.956 for 3D-US-EFW, p 0.71) with the GAP method could be demonstrated.

CONCLUSIONS

Within a population at risk of fetal macrosomia the performance of 3D-US-EFW is similar to that of 2D-US-EFW in the prediction of macrosomia at term regardless of the method used for the projection of the EFW, however different properties were noted between the two techniques. Such finding suggests a potential complementary role of the techniques which warrants evaluation in future research.

The use of magnetic resonance imaging in the prediction of birthweight

Extremes of fetal growth can increase adverse pregnancy outcomes, and this is equally applicable to single and multiple gestations. Traditionally, these cases have been identified using simple two-dimensional ultrasound which is quite limited by its low precision. Magnetic resonance imaging (MRI) has now been used for many years in obstetrics, mainly as an adjunct to ultrasound for congenital abnormalities and increasingly as part of the post-mortem examination. However, MRI can also be used to accurately assess fetal weight as first demonstrated by Baker et al in 1994, using body volumes rather than standard biometric measurements. This publication was followed by several others, all of which confirmed the superiority of MRI; however, despite this initial promise, the technique has never been successfully integrated into clinical practice. In this review, we provide an overview of the literature, detail the various techniques and formulas currently available, discuss the applicability to specific high-risk groups and present our vision for the future of MRI within clinical obstetrics.

Evidence-based recommendations for energy intake in pregnant women with obesity

BACKGROUND

In women with obesity, excess gestational weight gain (≥270 g/week) occurs in two out of three pregnancies and contributes to metabolic impairments in both mother and baby. To improve obstetrical care, objectively assessed information on energy balance is urgently needed. The objective of this study was to characterize determinants of gestational weight gain in women with obesity.

METHODS

This was a prospective, observational study of pregnant women with obesity. The primary outcome was energy intake calculated by the energy intake-balance method. Energy expenditure was measured by doubly-labeled water and whole-room indirect calorimetry and body composition as 3-compartment model by air displacement plethysmography and isotope dilution in early (13-16 weeks) and late pregnancy (35-37 weeks).

RESULTS

In pregnant women with obesity (n=54), recommended weight gain (n=8, 15%) during the second and third trimesters was achieved when energy intake was 125±52 kcal/d less than energy expenditure. In contrast, women with excess weight gain (67%) consumed 186±29 kcal/d more than they expended (P<0.001). Energy balance affected maternal adiposity (recommended: -2.5±0.8 kg fat mass, excess: +2.2±0.5, inadequate: -4.5±0.5, P<0.001), but not fetal growth. Weight gain was not related to demographics, activity, metabolic biomarkers, or diet quality. We estimated that energy intake requirements for recommended weight gain during the second and third trimesters were not increased as compared to energy requirements early in pregnancy (34±53 kcal/d, P=0.83).

CONCLUSIONS

We here provide the first evidence-based recommendations for energy intake in pregnant women with obesity. Contrary to current recommendations, energy intake should not exceed energy expenditure.

FUNDING

This study was funded by the National Institutes of Health (R01DK099175; Redman, U54GM104940 and P30DK072476; Core support).

TRIAL REGISTRATION

clinicaltrials.gov: NCT01954342.

Birth weight prediction models for the different gestational age stages in a Chinese population

The study aims to develop new birth weight prediction models for different gestational age stages using 2-dimensional (2D) ultrasound measurements in a Chinese population. 2D ultrasound was examined in pregnant women with normal singleton within 3 days prior to delivery (28–42 weeks’ gestation). A total of 19,310 fetuses were included in the study and randomly split into the training group and the validation group. Gestational age was divided into five stages: 28–30, 31–33, 34–36, 37–39 and 40–42 weeks. Multiple linear regression (MLR), fractional polynomial regression (FPR) and volume-based model (VM) were used to develop birth weight prediction model. New staged prediction models (VM for 28–36 weeks, MLR for 37–39 weeks, and FPR for 40–42 weeks) provided lower systematic errors and random errors than previously published models for each gestational age stage in the training group. The similar results were observed in the validation group. Compared to the previously published models, new staged models had the lowest aggregate systematic error (0.31%) and at least a 19.35% decrease; at least a 4.67% decrease for the root-mean-square error (RMSE). The prediction rates within 5% and 10% of birth weight for new staged models were higher than those for previously published models, which were 54.47% and 85.10%, respectively. New staged birth weight prediction models could improve the accuracy of birth weight estimation for different gestational age stages in a Chinese population.

ISUOG Practice Guidelines: ultrasound assessment of fetal biometry and growth

INTRODUCTION These Guidelines aim to describe appropriate assessment of fetal biometry and diagnosis of fetal growth disorders. These disorders consist mainly of fetal growth restriction (FGR), also referred to as intrauterine growth restriction (IUGR) and often associated with small‐for‐gestational age (SGA), and large‐for‐gestational age (LGA), which may lead to fetal macrosomia; both have been associated with a variety of adverse maternal and perinatal outcomes. Screening for, and adequate management of, fetal growth abnormalities are essential components of antenatal care, and fetal ultrasound plays a key role in assessment of these conditions. The fetal biometric parameters measured most commonly are biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur diaphysis length (FL). These biometric measurements can be used to estimate fetal weight (EFW) using various different formulae1. It is important to differentiate between the concept of fetal size at a given timepoint and fetal growth, the latter being a dynamic process, the assessment of which requires at least two ultrasound scans separated in time. Maternal history and symptoms, amniotic fluid assessment and Doppler velocimetry can provide additional information that may be used to identify fetuses at risk of adverse pregnancy outcome. Accurate estimation of gestational age is a prerequisite for determining whether fetal size is appropriate‐for‐gestational age (AGA). Except for pregnancies arising from assisted reproductive technology, the date of conception cannot be determined precisely. Clinically, most pregnancies are dated by the last menstrual period, though this may sometimes be uncertain or unreliable. Therefore, dating pregnancies by early ultrasound examination at 8–14 weeks, based on measurement of the fetal crown–rump length (CRL), appears to be the most reliable method to establish gestational age. Once the CRL exceeds 84 mm, HC should be used for pregnancy dating2–4. HC, with or without FL, can be used for estimation of gestational age from the mid‐trimester if a first‐trimester scan is not available and the menstrual history is unreliable. When the expected delivery date has been established by an accurate early scan, subsequent scans should not be used to recalculate the gestational age1. Serial scans can be used to determine if interval growth has been normal. In these Guidelines, we assume that the gestational age is known and has been determined as described above, the pregnancy is singleton and the fetal anatomy is normal. Details of the grades of recommendation used in these Guidelines are given in Appendix 1. Reporting of levels of evidence is not applicable to these Guidelines.

Prediction of birth weight in twin pregnancies using fractional limb volumes by three-dimensional ultrasonography

Objective: To predict birth weight using fetal fractional limb volumes (FLVs) by three-dimensional (3D) ultrasonography in twin pregnancies.Method: This prospective observational cohort study evaluated 51 twin pregnancies, including 28 dichorionic and 23 monochorionic pregnancies. Ultrasound examinations were performed up to 5 d before delivery. Birth weight prediction models were developed using the fractional arm volume (FAV), fractional thigh volume (FTV), and Hadlock's formula and were compared with the actual birth weight.Results: The mean gestational age at the time of ultrasound examination was 35.3 weeks. The mean birth weight was slightly higher in dichorionic than in monochorionic pregnancies 2391.2 versus 2352.4 g. The measurements using FTV were the closest to actual birth weights. For the total group, the Hadlock formula had mean percentage change of 7.18% while the FTV model presented mean percentage change of 6.62% in relation to birth weight. However, no significant difference was noted between Hadlock's formula and FTV p = .363 and .678 for dichorionic and monochorionic pregnancies, respectively.Conclusions: FTV accurately predicted birth weight in twin monochorionic and dichorionic pregnancies. However, Hadlock's formula should still be used.

Two-dimensional fetal biometry versus three-dimensional fractional thigh volume for ultrasonographic prediction of birthweight

OBJECTIVE

To develop and validate birthweight prediction models using fetal fractional thigh volume (TVol) in an Indian population, comparing them with existing prediction models developed for other ethnicities.

METHODS

A prospective observational study was conducted among 131 pregnant women (>36 weeks) attending a tertiary hospital in New Delhi, India, for prenatal care between December 1, 2014, and November 1, 2016. Participants were randomly divided into formulating (n=100) and validation (n=31) groups. Multiple regression analysis was performed to generate four models to predict birthweight using various combinations of two-dimensional (2D) ultrasonographic parameters and a three-dimensional (3D) ultrasonographic parameter (TVol). The best fit model was compared with previously published 2D and 3D models.

RESULTS

The best fit model comprised biparietal diameter, head circumference, abdominal circumference, and TVol. This model had the lowest mean percentage error (0.624 ± 8.075) and the highest coefficient of determination (R² =0.660). It correctly predicted 70.2% and 91.6% of birthweights within 5% and 10% of actual weight, respectively. Compared with previous models, attributability for the 2D and 3D models was 0.65 and 0.55, respectively. Accuracy was -0.05 ± 1.007 and -2.54 ± 1.11, respectively.

CONCLUSION

Models that included TVol provided good prediction of birthweight in the target population.

Accuracy of sonographic estimated fetal weight in suspected macrosomia: the likelihood of overestimating and underestimating the true birthweight

Objective: Macrosomia has increased risk of serious adverse outcomes for both infants and their mothers. As such, many providers recommend induction of labor or cesarean delivery (CD) based on sonographic estimated fetal weight (sonoEFW) cutoffs. It is known that sonoEFW is a poor predictor of birthweight (BW), especially at the extremes of weight. It is not clear, however, whether sonoEFWs tend to underestimate or overestimate the true BW among fetuses with suspected macrosomia. The objective of this study was to compare rates of overestimation of BW among women with suspected macrosomia by sonoEFW.Methods: This was a retrospective cohort study of women who presented to a single maternal-fetal medicine ultrasound unit within 2 weeks prior to delivery from January 2011 to November 2017. We identified women who received a sonoEFW ≥4000 g. The study sample was divided into four sonoEFW categories: 4000-4249, 4250-4499, 4500-4749, and ≥4750 g. Accuracy of sonoEFW was compared across groups, with the primary outcome being overestimation of BW.Results: A total of 502 patients were included, of whom 301 (60.1%) had a sonoEFW 4000-4249 g, 135 (26.9%) had a sonoEFW 4250-4499 g, 45 (9.0%) had a sonoEFW 4500-4749 g, and 21 (4.2%) had a sonoEFW ≥4750 g. In each sonoEFW group, the risk of overestimating BW was greater than 50%, and the likelihood of overestimation of BW increased significantly across sonoEFW groups (69.4, 76.3, 80.0, 95.2%, p < .001). This held true after adjusting for differences in baseline characteristics, including diabetes and amniotic fluid index. BW ≥4500 g was not accurately predicted. Among women with sonoEFW 4500-4749 g, only 28.9% delivered a neonate with a BW >4500 g; for women with a sonoEFW ≥4750 g, only 47.6% had a BW >4500 g. One hundred sixty-one (32.1%) women underwent CD for suspected macrosomia. Of these CDs, 48 (29.8%) of neonates had a BW <4000 g and 134 (83.2%) had a BW <4500 g.Conclusion: In patients undergoing sonoEFW within 2 weeks of delivery, sonoEFWs ≥4000 g are significantly more likely to overestimate than underestimate the true BW. Obstetricians should be cautious about intervening based on sonoEFW alone, given the high risk that this value is an overestimation of the true weight.

Current knowledge on the use of ultrasound measurements of fetal soft tissues for the assessment of pregnancy development

Ultrasonography, with its detailed imaging of the fetus, is very widely used in obstetrics. The primary aim of ultrasound scanning in pregnancy is to limit the risk of obstetric complications by early detection of abnormalities, such as intrauterine growth restriction and macrosomia. Currently, morphometric formulae are used for estimating fetal weight. They utilize basic biometric parameters. However, Hadlock formula, used for fetal weight estimation, has an error rate of 20%. For this reason, researchers all over the world have been looking for other sonographic parameters correlating with fetal weight, with a higher predictive value. The current scientific reports indicate that new sonographic parameters, such as soft tissue thickness values, are useful for fetal weight assessment. The measurements can be conducted in various parts of the fetus’s body, e.g. thigh, upper arm, abdomen or the subscapular area. Different types of measurements are characterized by different levels of correlation with other sonographic and anthropometric parameters as well as body mass and gestational age. Based on the reports, numerous studies proposing new fetal weight calculation formulae have been produced. Apart from soft tissue, some more advanced and detailed measurements are taken, such as those involving adipose and lean tissue or using three-dimensional ultrasound (3D), for determining fetal weight. Ultrasound measurement of subcutaneous tissue thickness in various parts of the body may prove to be a strong predictor of fetal weight, which is useful for sonographic assessment of pregnancy.

Fractional fetal thigh volume in the prediction of normal and abnormal fetal growth during the third trimester of pregnancy

Background

Currently, 2-dimensional ultrasound estimation of fetal size rather than fetal growth is used to define fetal growth restriction, but single estimates in late pregnancy lack sensitivity and may identify small for gestational age rather than growth restriction. Single or longitudinal measures of 3-dimensional fractional thigh volume may address this problem.

Objective

We sought to derive normal values for 3-dimensional fractional thigh volume in the third trimester, determine if fractional thigh volume is superior to 2-dimensional ultrasound biometry alone for detecting fetal growth restriction, and determine whether individualized growth assessment parameters have the potential to identify fetal growth restriction remote from term delivery.

Study Design

This was a longitudinal prospective cohort study of 115 unselected pregnancies in a tertiary referral unit (St Mary’s Hospital, Manchester, United Kingdom). Standard 2-dimensional ultrasound biometry measurements were obtained, along with fractional thigh volume measurements (based on 50% of the femoral diaphysis length). Measurements were used to calculate estimated fetal weight (Hadlock). Individualized growth assessment parameters and percentage deviations in longitudinally measured biometrics were determined using a Web-based system (iGAP; http://iGAP.research.bcm.edu). Small for gestational age was defined <10th and fetal growth restriction <3rd customized birthweight centile. Logistic regression was used to compare estimated fetal weight (Hadlock), estimated fetal weight (biparietal diameter–abdominal circumference–fractional thigh volume), fractional thigh volume, and abdominal circumference for the prediction of small for gestational age or fetal growth restriction at birth. Screening performance was assessed using area under the receiver operating characteristic curve.

Results

There was a better correlation between fractional thigh volume and estimated fetal weight ((biparietal diameter–abdominal circumference–fractional thigh volume) obtained at 34-36 weeks with birthweight than between 2-dimensional biometry measures such as abdominal circumference and estimated fetal weight (Hadlock). There was also a modest improvement in the detection of both small for gestational age and fetal growth restriction using fractional thigh volume–derived measures compared to standard 2-dimensional measurements (area under receiver operating characteristic curve, 0.86; 95% confidence interval, 0.79–0.94, and area under receiver operating characteristic curve, 0.92; 95% confidence interval, 0.85–0.99, respectively).

Conclusion

Fractional thigh volume measurements offer some improvement over 2-dimensional biometry for the detection of late-onset fetal growth restriction at 34-36 weeks.

Automated Fractional Limb Volume Measurements Improve the Precision of Birth Weight Predictions in Late Third-Trimester Fetuses

OBJECTIVES

Fetal soft tissue can be assessed by using fractional limb volume as a proxy for in utero nutritional status. We investigated automated fractional limb volume for rapid estimate fetal weight assessment.

METHODS

Pregnant women were prospectively scanned for 2- and 3-dimensional fetal biometric measurements within 4 days of delivery. Performance of birth weight prediction models was compared: (1) Hadlock (Am J Obstet Gynecol 1985; 151:333-337; biparietal diameter, abdominal circumference, and femur diaphysis length); and (2) Lee (Ultrasound Obstet Gynecol 2009; 34:556-565; biparietal diameter, abdominal circumference, and automated fractional limb volume). Percent differences were calculated: [(estimated birth weight - actual birth weight) ÷ (actual birth weight] × 100. Systematic errors (accuracy) were summarized as signed mean percent differences. Random errors (precision) were calculated as ± 1 SD of percent differences.

RESULTS

Fifty neonates were delivered at 39.4 weeks' gestation. The Hadlock model generated the most accurate birth weight (0.31%) with a mean random error of ±7.9%. Despite systematic underestimations, the most precise results occurred with fractional arm volume (-9.1% ± 5.1%) and fractional thigh (-5.2% ± 5.2%) models. The size and distribution of these prediction errors were improved after correction for systematic errors.

CONCLUSIONS

Automated fractional limb volume measurements can improve the precision of weight predictions in third-trimester fetuses. Correction factors may be necessary to adjust underestimated systematic errors when using automated fractional limb volume with prediction models that are based on manual tracing of fetal limb soft tissue borders.

Intraexaminer and Interexaminer Variability in 3D Fetal Volume Measurements During the Second and Third Trimesters of Pregnancy

OBJECTIVES

To assess intraexaminer and interexaminer reliability of 3-dimensional fetal sonographic measurements.

METHODS

Three-dimensional fetal organ volumes (head, kidney, total thigh volume, and fractional thigh volume) were acquired during the second and third trimesters, with the addition of placental volume in the second trimester, by 2 different experienced, blinded sonographers. Fifty-eight fetuses were examined from 21 to 39 weeks' gestation. Intraexaminer and Interexaminer reliability was assessed with Bland-Altman plots, and their 95% limits of agreement and intraclass correlation coefficients.

RESULTS

The most significant interexaminer error was observed in the second-trimester kidney volume (95% limits of agreement, ± 110%), and the best agreement was for the third-trimester fractional thigh volume (95% limits of agreement, ± 25%) and second-trimester head volume (95% limits of agreement, -7%-25%). Second- and third-trimester intraclass correlation coefficient results were all greater than 0.75, apart from second-trimester kidney volume intraexaminer (0.374) and interexaminer (0.061) measurements, second-trimester placenta interexaminer measurements (0.390), and third-trimester kidney interexaminer measurements (0.647).

CONCLUSIONS

Three-dimensional fetal sonographic volumes of the head, kidney, total thigh, and placenta have limited reproducibility, and improvements in measurement techniques are needed before they can be used routinely to assess fetal growth. The 3-dimensional fractional thigh volume can be reliably obtained in the late third trimester.

The systematic error in the estimation of fetal weight and the underestimation of fetal growth restriction

Fetal growth restriction (FGR) is associated with an increased risk of perinatal morbidity and mortality and has lifetime implications for the risk of chronic medical conditions. Antenatal diagnosis of FGR remains poor, with the majority of cases remaining undiagnosed. Although several factors contribute to the underdiagnosis of FGR, the error in ultrasound estimation of fetal weight (EFW) generally is not considered in clinical practice. In this commentary, we suggest that the intrinsic, or systematic, error in ultrasound EFW is a significant factor contributing to the underestimation of fetuses predicted to have FGR and should be incorporated into screening and surveillance recommendations. To illustrate this point, we present an analytic model of published data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies characterizing and quantifying the impact of the systematic error in ultrasound EFW on the underdiagnosis of FGR. Independent of the centile at which the risk of adverse outcome related to FGR begins, whether the 10th, 5th or 3rd percentile, our analysis suggests the need to modify to the current paradigm for identifying and responding to fetuses estimated to be at risk.

Estimation of fetal weight in pregnancies past term

INTRODUCTION

The aim of the study was to investigate the accuracy of estimating fetal weight with ultrasound in pregnancies past term, using the eSnurra algorithm.

MATERIAL AND METHODS

In all, 419 women with pregnancy length of 290 days, attending a specialist consultation at Stavanger University Hospital, Norway, were included in a prospective observational study. Fetal weight was estimated using biparietal diameter (BPD) and abdominal circumference (AC). The algorithm implemented in an electronic calculation (eSnurra) was used to compute estimated fetal weight (EFW). Results were compared with birthweight (BW).

RESULTS

The mean interval between the ultrasound examination and birth was 2 days (SD 1.4). The median difference between BW and EFW was -6 g (CI -40 to +25 g) and the median percentage error was -0.1% (95% CI -1.0 to 0.6%). The median absolute difference was 190 g (95% CI 170-207 g). The BW was within 10% of EFW in 83% (95% CI 79-87%) of cases and within 15% of EFW in 94% (95% CI 92-96%) of cases. Limits of agreement (95%) were from -553 g to +556 g. Using 5% false-positive rates, the sensitivity in detecting macrosomic and small for gestational age fetuses was 54% (95% CI 35-72%) and 49% (95% CI 35-63%), respectively.

CONCLUSION

The accuracy of fetal weight estimation was good. Clinicians should be aware of limitations related to prediction at the upper and lower end, and the importance of choosing appropriate cut-off levels.

Single and Serial Fetal Biometry to Detect Preterm and Term Small- and Large-for-Gestational-Age Neonates: A Longitudinal Cohort Study

Objectives

To assess the value of single and serial fetal biometry for the prediction of small- (SGA) and large-for-gestational-age (LGA) neonates delivered preterm or at term.

Methods

A cohort study of 3,971 women with singleton pregnancies was conducted from the first trimester until delivery with 3,440 pregnancies (17,334 scans) meeting the following inclusion criteria: 1) delivery of a live neonate after 33 gestational weeks and 2) two or more ultrasound examinations with fetal biometry parameters obtained at ≤36 weeks. Primary outcomes were SGA (<5^th centile) and LGA (>95^th centile) at birth based on INTERGROWTH-21^st gender-specific standards. Fetus-specific estimated fetal weight (EFW) trajectories were calculated by linear mixed-effects models using data up to a fixed gestational age (GA) cutoff (28, 32, or 36 weeks) for fetuses having two or more measurements before the GA cutoff and not already delivered. A screen test positive for single biometry was based on Z-scores of EFW at the last scan before each GA cut-off so that the false positive rate (FPR) was 10%. Similarly, a screen test positive for the longitudinal analysis was based on the projected (extrapolated) EFW at 40 weeks from all available measurements before each cutoff for each fetus.

Results

Fetal abdominal and head circumference measurements, as well as birth weights in the Detroit population, matched well to the INTERGROWTH-21^st standards, yet this was not the case for biparietal diameter (BPD) and femur length (FL) (up to 9% and 10% discrepancy for mean and confidence intervals, respectively), mainly due to differences in the measurement technique. Single biometry based on EFW at the last scan at ≤32 weeks (GA IQR: 27.4–30.9 weeks) had a sensitivity of 50% and 53% (FPR = 10%) to detect preterm and term SGA and LGA neonates, respectively (AUC of 82% both). For the detection of LGA using data up to 32- and 36-week cutoffs, single biometry analysis had higher sensitivity than longitudinal analysis (52% vs 46% and 62% vs 52%, respectively; both p<0.05). Restricting the analysis to subjects with the last observation taken within two weeks from the cutoff, the sensitivity for detection of LGA, but not SGA, increased to 65% and 72% for single biometry at the 32- and 36-week cutoffs, respectively. SGA screening performance was higher for preterm (<37 weeks) than for term cases (73% vs 46% sensitivity; p<0.05) for single biometry at ≤32 weeks.

Conclusions

When growth abnormalities are defined based on birth weight, growth velocity (captured in the longitudinal analysis) does not provide additional information when compared to the last measurement for predicting SGA and LGA neonates, with both approaches detecting one-half of the neonates (FPR = 10%) from data collected at ≤32 weeks. Unlike for SGA, LGA detection can be improved if ultrasound scans are scheduled as close as possible to the gestational-age cutoff when a decision regarding the clinical management of the patient needs to be made. Screening performance for SGA is higher for neonates that will be delivered preterm.

Three-Versus Two-Dimensional Sonographic Biometry for Predicting Birth Weight and Macrosomia in Diabetic Pregnancies

OBJECTIVES

The purpose of this study was to test the hypothesis that a formula incorporating 3-dimensional (3D) fractional thigh volume would be superior to the conventional 2-dimensional (2D) formula of Hadlock et al (Am J Obstet Gynecol 1985; 151:333-337) for predicting birth weight and macrosomia.

METHODS

We conducted a prospective cohort study of pregnancies complicated by pregestational or gestational diabetes and delivered after 38 weeks. Two-dimensional and 3D sonographic examinations were performed for fetal biometry and factional thigh volumes at 34 to 37 weeks. Fetal weight was estimated by Hadlock's 2D formula IV, which uses only 2D biometry, and formula 6 from Lee et al (Ultrasound Obstet Gynecol 2009; 34:556-565), which incorporates 3D fractional thigh volume and 2D biometry. The gestation-adjusted projection method was used to estimate predicted birth weights from 2D and 3D estimates. The primary outcome was fetal macrosomia, which was defined as birth weight of 4000 g or higher.

RESULTS

A total of 115 women with diabetes met inclusion criteria, and 17 (14.8%) delivered macrosomic neonates. The mean percentage error was significantly lower for the 2D than the 3D projected estimate (1.0% versus 12.0%; P < .01). The standard deviation of the mean percentage error was also significantly lower for the 2D projected estimate (10.2% versus 17.2%; P< .01). Two-dimensional biometry was overall superior to 3D biometry for predicting macrosomia (area under the receiver operating characteristic curve, 0.88 versus 0.75; P = .03). Specificity was significantly higher for 2D biometry (85% versus 66%; P < .01), whereas the difference in sensitivity was not statistically significant (59% versus 71%; P = .22).

CONCLUSIONS

In this study, the Hadlock 2D formula was superior to the 3D method for predicting birth weight and macrosomia in diabetic women when used approximately 2 weeks before delivery, based on the gestation-adjusted projection method.

A New Sonographic Weight Estimation Formula for Small-for-Gestational-Age Fetuses

OBJECTIVES

The purpose of this study was to develop a new specific weight estimation formula for small-for-gestational-age (SGA) fetuses that differentiated between symmetric and asymmetric growth patterns.

METHODS

A statistical estimation technique known as component-wise gradient boosting was applied to a group of 898 SGA fetuses (symmetric, n = 750; asymmetric, n = 148). A new formula was derived from the data obtained and was then compared to other commonly used equations.

RESULTS

The new formula derived is as follows: estimated fetal weight = e^[1.3734627 + 0.0057133 × biparietal diameter + 0.0011282 × head circumference + 0.0201147 × abdominal circumference + 0.0183081 × femur length - 0.0000177 × biparietal diameter(2) - 0.0000018 × head circumference(2) - 0.0000297 × abdominal circumference(2) -0.0001007 × femur length(2) + 0.0397563 × I(sex = male) + 0.0064505 × gestational age (days) + 0.0096528 × I(SGA = asymmetric)], where the function I denotes an indicator function, which is 1 if the expression is fulfilled (sex = male; SGA type = asymmetric) and otherwise 0. In the whole study group and the 2 subgroups, the new formula showed the lowest median absolute percentage error, mean percentage error, and random error and the best distribution of absolute percentage errors within prespecified error bounds.

CONCLUSIONS

The new formula substantially improves weight estimation in SGA fetuses.

A Novel Semiautomated Fractional Limb Volume Tool for Rapid and Reproducible Fetal Soft Tissue Assessment

The purpose of this study was to document the reproducibility and efficiency of a semiautomated image analysis tool that rapidly provides fetal fractional limb volume measurements. Fifty pregnant women underwent 3-dimensional sonographic examinations for fractional arm and thigh volumes at a mean menstrual age of 31.3 weeks. Manual and semiautomated fractional limb volume measurements were calculated, with the semiautomated measurements calculated by novel software (5D Limb Vol; Samsung Medison, Seoul, Korea). The software applies an image transformation method based on the major axis length, minor axis length, and limb center coordinates. A transformed image is used to perform a global optimization technique for determination of an optimal limb soft tissue boundary. Bland-Altman analysis defined bias with 95% limits of agreement (LOA) between methods, and timing differences between manual versus automated methods were compared by a paired t test. Bland-Altman analysis indicated an acceptable bias with 95% LOA between the manual and semiautomated methods: mean arm volume ± SD, 1.7% ± 4.6% (95% LOA, -7.3% to 10.7%); and mean thigh volume, 0.0% ± 3.8% (95% LOA, -7.5% to 7.5%). The computer-assisted software completed measurements about 5 times faster compared to manual tracings. In conclusion, semiautomated fractional limb volume measurements are significantly faster to calculate when compared to a manual procedure. These results are reproducible and are likely to reduce operator dependency. The addition of computer-assisted fractional limb volume to standard biometry may improve the precision of estimated fetal weight by adding a soft tissue component to the weight estimation process.

Comparison of 2- and 3-Dimensional Sonography for Estimation of Birth Weight and Neonatal Adiposity in the Setting of Suspected Fetal Macrosomia

OBJECTIVES

To compare the accuracy of 2-dimensional (2D) and 3-dimensional (3D) fetal measurements for prediction of birth weight Z score and neonatal adiposity (percent body fat) in the setting of suspected fetal macrosomia.

METHODS

We conducted a prospective observational study of term singleton pregnancies with suspected macrosomia. Patients were enrolled on admission to labor and delivery and underwent sonographic examinations. Within 48 hours of delivery, neonatal anthropometric measurements were obtained.

RESULTS

Thirty-four neonates were included in the analysis. Mothers were very obese (mean body mass index ± SD, 39.1 ± 7.8 kg/m(2)); 56.5% were white; and 39.1% had diabetes. Neonates were 38% female and had a mean birth weight of 3940.0 ± 496.8 g, percent body fat of 18.5% ± 4.0%, and Ponderal index of 2.8 ± 0.3 g/cm(3). Mean 2D estimated fetal weight was 3973 ± 443 g; mean 3D estimated fetal weight was 3803 ± 528 g; and mean thigh volume was 102.5 ± 19.6 cm(3). Both 2D and 3D measurements accounted for about half the variance in predicted birth weight (R(2) for 2D = 0.53, 71% within 10% of birth weight; R(2) for 3D = 0.47, 65% within 10% of birth weight). Thigh volume Z score was the prenatal parameter most highly correlated with both birth weight Z score (R(2) = 0.52; r = 0.72; 95% confidence interval, 0.54-0.84; P < .001) and percent body fat (R(2) = 0.22; r = 0.47; 95% confidence interval, 0.17-0.69; P = .04).

CONCLUSIONS

In our population of fetuses with suspected macrosomia, fractional thigh volume was the best sonographic estimate of neonatal percent body fat and birth weight Z score. Future research on prediction of neonatal weight and adiposity in macrosomic fetuses should include an estimate of fetal soft tissue given the generalized increase in body fat of these fetuses.

3D and 2D ultrasound-based fetal weight estimation: a single center experience

OBJECTIVE

Evaluate two new 3D and two new 2D ultrasound formulae for fetal weight estimation against the modified Hadlock formula and compare their estimation to the actual fetal weight.

METHODS

Fifty pregnant females were included.

INCLUSION CRITERIA

singleton pregnancy, within five days of delivery and normal or IUGR pregnancy. 3D evaluation of the fetal thigh and arm was done to calculate mid-thigh and mid-arm volumes. The actual fetal weight was recorded at delivery and compared to the estimated weights.

RESULTS

Modified Hadlock formula had higher accuracy, whereas fractional limb volume method had higher precision. Systematic errors for the modified Hadlock formula, Model 6 of fractional limb volume and the original mid-thigh soft tissue thickness methods were 2.3%, -4.8% and 11%, respectively, whereas the random errors were 7.7%, 6.2% and 13.8%, respectively. The percentage of cases estimated within 5%, 10% and 15% of actual fetal weight were 48%, 86% and 92%, respectively, for the modified Hadlock method, whereas for the fractional limb volume method, these were 40%, 78% and 98%, respectively.

CONCLUSION

Fractional limb volume method is a very promising method for fetal weight estimation. Its performance is not significantly different from the modified Hadlock method.

Personalized third-trimester fetal growth evaluation: comparisons of individualized growth assessment, percentile line and conditional probability methods

OBJECTIVE

To compare third-trimester size trajectory prediction errors (average transformed percent deviations) for three individualized fetal growth assessment methods.

METHODS

This study utilized longitudinal measurements of nine directly measured size parameters in 118 fetuses with normal neonatal growth outcomes. Expected value (EV) function coefficients and variance components were obtained using two-level random coefficient modeling. Growth models (IGA) or EV coefficients and variance components (PLM and CPM) were used to calculate predicted values at ∼400 third-trimester time points. Percent deviations (%Dev) calculated at these time points using all three methods were expressed as percentages of IGA MA-specific reference ranges [transformed percent deviations (T%Dev)]. Third-trimester T%Dev values were averaged (aT%Dev) for each parameter. Mean ± standard deviation's for sets of aT%Dev values derived from each method (IGA, PLM and CPM) were calculated and compared.

RESULTS

Mean aT%Dev values for nine parameters were: (i) IGA: -4.3 to 5.2% (9/9 not different from zero); (ii) PLM: -32.7 to 25.6% (4/9 not different from zero) and (iii) CPM: -20.4 to 17.4% (5/9 not different from zero). Seven of nine systematic deviations from zero were statistically significant when IGA values were compared to either PLM or CPM values. Variabilities were smaller for IGA when compared to those for PLM or CPM, with (i) 5/9 being statistically significant (IGA versus PLM), (ii) 2/9 being statistically significant (IGA versus CPM) and (iii) 5/9 being statistically significant (PLM versus CPM).

CONCLUSIONS

Significant differences in the agreement between predicted third-trimester size parameters and their measured values were found for the three methods tested. With most parameters, IGA gave smaller mean aT%Dev values and smaller variabilities. The CPM method was better than the PLM approach for most but not all parameters. These results suggest that third-trimester size trajectories are best characterized by IGA in fetuses with normal growth outcomes.

Ultrasound estimation of birth weight in twin pregnancy: comparison of biometry algorithms in the STORK multiple pregnancy cohort

OBJECTIVES

The aims of this study were first, to ascertain the accuracy of formulae for ultrasonographic birth-weight estimation in twin compared with singleton pregnancies and second, to assess the accuracy of sonographic examination in the prediction of birth-weight discordance in twin pregnancies.

METHODS

This was a retrospective cohort study including both singleton and twin pregnancies. Routine biometry was recorded and estimated fetal weight (EFW) calculated using 33 different formulae. Only pregnancies that delivered within 48 h of the ultrasound scan were included (4280 singleton and 586 twin fetuses). Differences between the EFW and actual birth weight (ABW) were assessed by percentage error, accuracy in predictions within ± 10% and ± 15% of error and use of the Bland-Altman method. The accuracy of prediction of the different cut-offs of birth-weight discordance in twin pregnancies was also assessed using the area under the receiver-operating characteristics curve (AUC).

RESULTS

The overall mean absolute percentage error was ≤ 10% for 25 formulae in singleton pregnancies compared with three formulae in twin pregnancies. The overall predictions within ± 10% and ± 15% of the ABW were 62.2% and 81.5% in singleton and 49.7% and 68.5% in twin pregnancies, respectively. When t e formulae were categorized according to the biometric parameters included, those based on a combination of head, abdomen and femur measurements showed the lowest mean absolute percentage error, in both singleton and twin pregnancies. The predictive accuracy for 25% birth-weight discordance using the Hadlock 2 formula, as assessed by the AUC, was 0.87.

CONCLUSIONS

Ultrasound estimation of birth weight is less accurate in twin than in singleton pregnancies. Formulae that include a combination of head, abdomen and femur measurements perform best in both singleton and twin pregnancies.

Fetal growth cessation in late pregnancy: its impact on predicted size parameters used to classify small for gestational age neonates

OBJECTIVE

To evaluate the impact of late 3rd trimester fetal growth cessation on anatomical birth characteristic predictions used in classifying SGA neonates.

METHODS

A prospective longitudinal study was performed in 119 pregnancies with normal neonatal growth outcomes. Seven biometric parameters were measured at 3-4 weeks intervals using 3D ultrasonography. Rossavik size models were determined to predict birth characteristics at different ages. Percent Differences (% Diff) were calculated from predicted and measured birth characteristics. Growth Cessation Ages (GCA) were identified when no systematic change in % Diff values occurred after specified prediction ages. Systematic and random prediction errors were compared using different assumptions about the GCA. Predicted and measured size parameters were used to determine six new Growth Potential Realization Index (GPRI) reference ranges. Five were used to sub-classify 34 SGA neonates (weight < 10th percentile) based on the number of abnormal GPRI values.

RESULTS

Growth cessation ages were 38 weeks for HC, AC, mid-thigh circumference, estimated weight and mid-arm circumference. Crown-heel length GCA was 38.5 weeks. At GCA, birth characteristics had prediction errors that varied from 0.08 ± 3.4% to 15.7 ± 9.1% and zero % Diff slopes after 38 weeks. Assuming growth to delivery gave increased systematic and random prediction errors as well as positive % Diff slopes after 38 weeks, MA. Seventeen of the SGA neonates had 0 or 1 abnormal GPRI values [Subgroup 1] and 17 others had 2 or more abnormal values [Subgroup 2]. In Subgroup 1, 4/85 (4.7%) of GPRI's were abnormal while in Subgroup 2, 43/85 (50.6%) were abnormal. Use of only one type of GPRI for SGA subclassification resulted in substantial false negative and some false positive rates when compared to subclassification based on all five GPRI values.

CONCLUSIONS

Growth cessation occurred at approximately 38 weeks for all six birth characteristics studied. SGA neonates can be separated into normal and growth restricted subgroups based on the frequency of abnormal GPRI values (GPRI Profile Classification).

A modified prenatal growth assessment score for the evaluation of fetal growth in the third trimester using single and composite biometric parameters

OBJECTIVE

To define modified Prenatal Growth Assessment Scores (mPGAS) for single and composite biometric parameters and determine their reference ranges in normal fetuses.

METHODS

Nine anatomical parameters (ap) were measured and the weight estimated (EWTa, EWTb) in a longitudinal study of 119 fetuses with normal neonatal growth outcomes. Expected third trimester size trajectories, obtained from second trimester Rossavik size models, were used in calculating Percent Deviations (% Dev's) and their age-specific reference ranges in each fetus. The components of individual % Dev's values outside their reference ranges, designated +iapPGAS, -iapPGAS, were averaged to give +apPGAS and -apPGAS values for the 3rd trimester. The +iapPGAS and -iapPGAS values for different combinations of ap (c1a (HC, AC, FDL, ThC, EWTa), c1b (HC, AC, FDL, ThC, EWTb), c2 (ThC, ArmC, AVol, TVol), c3 (HC, AC, FDL, EWTa)) were then averaged to give +icPGAS and -icPGAS values at different time points or at the end of the third trimester (+cPGAS, -cPGAS). Values for iapPGAS, ic1bPGAS, and ic2PGAS were compared to their respective apPGAS or cPGAS reference ranges.

RESULTS

All mPGAS values had one 95% range boundary at 0.0%. Upper boundaries of 1D +apPGAS values ranged from 0.0% (HC) to +0.49% (ThC) and were +0.06%, +2.3% and +1.8% for EWT, AVol and TVol, respectively. Comparable values for -apPGAS were 0.0% (BPD, FDL, HDL), to -0.58% (ArmC), -0.13% (EWT), -0.8% (AVol), and 0.0% (TVol). The +cPGAS, 95% reference range upper boundaries varied from +0.36% (c1b) to +0.89% (c2). Comparable values for -cPGAS lower boundaries were -0.17% (c1b) to -0.43% (c2).

CONCLUSIONS

The original PGAS concept has now been extended to individual biometric parameters and their combinations. With the standards provided, mPGAS values can now be tested to see if detection of different types of third trimester growth problems is improved.

End-of-life decisions for extremely low-gestational-age infants: why simple rules for complicated decisions should be avoided

Interventions for extremely preterm infants bring up many ethical questions. Guidelines for intervention in the "periviable" period generally divide infants using predefined categories, such as "futile," "beneficial," and "gray zone" based on completed 7-day periods of gestation; however, such definitions often differ among countries. The ethical justification for using gestational age as the determination of the category boundaries is rarely discussed. Rational criteria used to make decisions regarding life-sustaining interventions must incorporate other important prognostic information. Precise guidelines based on imprecise data are not rational. Gestational age-based guidelines include an implicit judgment of what is deemed to be an unacceptably poor chance of "intact" survival but fail to explore the determination of acceptability. Furthermore, unclear definitions of severe disability, the difficulty, or impossibility, of accurately predicting outcome in the prenatal or immediate postnatal period make such simplistic formulae inappropriate. Similarly, if guidelines for intervention for the newborn are based on the "qualitative futility" of survival, it should be explicitly stated and justified according to established ethical guidelines. They should discuss whether newborn infants are morally different to older individuals or explain why thresholds recommended for intervention are different to recommendations for those in older persons. The aim should be to establish individualized goals of care with families while recognizing uncertainty, rather than acting on labels derived from gestational age categories alone.

Fetal weight estimation in gestational diabetic pregnancies: comparison between conventional and three-dimensional fractional thigh volume methods using gestation-adjusted projection

OBJECTIVES

To evaluate the accuracy of gestation-adjusted birth-weight estimation using a three-dimensional (3D) fractional thigh volume (TVol) method in pregnant women with gestational diabetes mellitus (GDM), and to compare it with the conventional two-dimensional method of Hadlock et al.

METHODS

Pregnant women with GDM were referred at 34 to 36 + 6 weeks' gestation for ultrasound examination. Estimated fetal weight (EFW) was obtained using both the Hadlock and the TVol methods. Using a gestation-adjusted projection method, predicted birth weight was compared to actual birth weight at delivery.

RESULTS

Based on 125 pregnancies, the TVol method with gestation-adjusted projection had a mean (± SD) percentage error in estimating birth weight of -0.01 ± 5.0 (95% CI, -0.96 to 0.98)% while the method of Hadlock with gestation-adjusted projection had an error of 1.28 ± 9.1 (95% CI, -0.33 to 2.87)%. The mean percentage error of the two methods was significantly different (P = 0.039), while the random error was not (P = 1.0). For the prediction of macrosomia (birth weight ≥ 4000 g, n = 19), sensitivity was 84 and 63% for the TVol and Hadlock methods, respectively (95% CI for difference -2 to 44%, P = 0.22) and specificity was 96 and 89% for the TVol and Hadlock methods, respectively (95% CI for difference 5-9%, P = 0.01).

CONCLUSIONS

In women with GDM, a new method of estimating birth weight based on 3D-TVol measurements performed at 34 + 0 to 36 + 6 weeks' gestation and gestation-adjusted projection of estimated fetal weight, is more accurate than the standard method based on Hadlock's formula in predicting birth weight. The TVol method has comparable sensitivity but higher specificity than the Hadlock method in predicting neonatal macrosomia.

Sex-related growth differences are present but not enhanced in in vitro fertilization pregnancies

OBJECTIVE

To determine whether IVF modifies the effect of fetal sex on growth.

DESIGN

Retrospective cohort study.

SETTING

Tertiary care center and related facilities.

PATIENT(S)

Singleton live births without fetal/maternal comorbidities from fertile women who conceived without the use of assisted reproductive technologies and infertile women who conceived with IVF.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The primary outcome was birth weight (BW). Secondary outcomes were fetal crown-rump length (CRL) in the first trimester, biparietal diameter (BPD), and estimated fetal weight (EFW) in the second trimester.

RESULT(S)

There were no differences in baseline characteristics between women carrying male fetuses and those carrying female fetuses in either mode of conception. In unadjusted analyses, the male-female differentials in fetal BPD and BW were more pronounced in the IVF cohort than in the unassisted cohort. In multivariable regression analysis, male BPD exceeded female BPD by 0.12 cm, male EFW exceeded female EFW by 12 g, and male BW exceeded female BW by 172 g. IVF did not have a significant effect on BPD but was associated with a 52 g increase in EFW in the midgestation. IVF was associated with an 81-g reduction in BW. IVF did not modify the magnitude of size differences between the sexes in the midgestation or at birth.

CONCLUSION(S)

Comparable sex-dependent differential growth occurs in unassisted and IVF pregnancies.

Individualized fetal growth assessment: critical evaluation of key concepts in the specification of third trimester size trajectories

OBJECTIVES

To characterize second and third trimester fetal growth using Individualized Growth Assessment methods in a larger cohort of fetuses with normal neonatal growth outcomes.

METHODS

A prospective longitudinal study of 119 pregnancies was performed from 18 weeks, MA, to delivery. Measurements of several 1D and 3D fetal size parameters were obtained from 3D volume data sets at 3-4 week intervals. Regression analyses were used to determine Start Points (SP) and Rossavik model (P = c {t} (k + st)) coefficients c. k and s for each parameter in each fetus. Second trimester growth velocity reference ranges were determined and size model specification functions re-established, the latter used to generate individual size models. Actual measurements were compared to predicted third trimester size trajectories using Percent Deviations. New age-specific reference ranges for the Percent Deviations of each parameter were defined using 2-level statistical modeling.

RESULTS

Rossavik models fit the data for all parameters very well (R(2): 99%), with SP's and k values similar to those found in much smaller cohorts. The c* values were strongly related to the second trimester slope (R(2): 97%), as was predicted s* to estimated c* (R(2): 54--95%). Rossavik models predicted third trimester growth with systematic errors close to 0%; random errors (95% range) ranged between 5.7 and 10.9% and 20.0 and 24.3% for 1D and 3D parameters, respectively.

CONCLUSIONS

IGA procedures for evaluating second and third trimester growth are now established based on a larger cohort (4-6 fold larger). New, more rigorously defined, age-specific standards for the evaluation of third trimester size deviations are now available for nine anatomical parameters and a weight estimation procedure that incorporates a soft tissue parameter (fractional thigh volume). These results provide a means for more reliably assessing fetal growth on an individualized basis, thus minimizing the effect of biological differences in growth.

Prospective validation of fetal weight estimation using fractional limb volume

OBJECTIVES

To prospectively validate the use of fractional limb volume measurements for estimated fetal weight (EFW) during the second and third trimesters of pregnancy and to summarize the medical literature regarding application of fractional limb volume for fetal weight estimation.

METHODS

One hundred and sixty-four women prospectively underwent three-dimensional ultrasonography within 4 days of delivery. Birth weights (BWs) ranged from 390 to 5426 g. Fetal measurements were extracted using volume datasets for biparietal diameter, abdominal circumference, femur diaphysis length, fractional arm volume and fractional thigh volume. Fractional limb volumes were manually traced from a central portion of the humerus or femur diaphysis. Mean percentage differences and SDs of the percentage differences were calculated for EFW. The proportion of newborns with EFW within 5 or 10% of BW were compared with an estimate obtained using a Hadlock formula that was modified using model coefficients from the same local population sample.

RESULTS

Ultrasound scans were performed between 21.7 and 42 weeks' menstrual age. Optimal model performance (1.9 ± 6.6%) resulted from using a combination of biparietal diameter, abdominal circumference and fractional thigh volume. The precision of this model was superior to results obtained using a modified Hadlock model (1.1 ± 8.4%), although accuracy of these predictions was slightly decreased for female infants. For all fetuses, the prediction model that incorporated fractional thigh volume correctly classified a greater proportion of EFW within 5% (55.1 vs 43.7%; P = 0.03) or 10% (86.5 vs 75.9%; P < 0.05) of BW when compared with the modified Hadlock model.

CONCLUSIONS

Fractional thigh volume can be added to two-dimensional sonographic measurements of the head and trunk to improve the precision of fetal weight estimation. This approach permits the inclusion of soft tissue development as part of a weight estimation procedure for the assessment of generalized fetal nutritional status.