Standardization of fetal ultrasound biometry measurements: improving the quality and consistency of measurements

Use of focus point for plane acquisition to improve reproducibility in fetal biometry

OBJECTIVE

To assess the reproducibility of ultrasound measurements of fetal biometry using a 'focus point' to assist the acquisition of the relevant plane.

METHODS

This was a study of 80 women with a singleton non-anomalous pregnancy who attended University College London Hospital, London, UK, between 18 and 37 weeks' gestation. Planes to measure head circumference (HC), abdominal circumference (AC) and femur length (FL) were obtained four times by two different sonographers with different levels of experience, who were blinded to one another; the first set of images was obtained with reference to a standard image, and the second set of images was obtained using the focus point technique. The focus point was defined as a unique fetal anatomical landmark in each plane (cavum septi pellucidi for HC, two-thirds of the umbilical vein for AC and one of the two extremities of the diaphysis for FL). Once identified, the focus point was maintained in view while the sonographer rotated the probe along three axes (x, y, z) to acquire the relevant plane. Sonographers were either in training or had > 3000 scans worth of experience. Intra- and interobserver reproducibility were assessed using Bland-Altman plots, and absolute values and percentages for mean difference and 95% limits of agreement (LoA) were reported.

RESULTS

Overall reproducibility was good, with all 95% LoA < 8%. Reproducibility was improved by use of the focus point compared with the standard technique for both intraobserver comparison (95% LoA, < 4% vs < 6%) and interobserver comparison (95% LoA, < 7% vs < 8%). These findings were independent of sonographer seniority and plane acquired.

CONCLUSIONS

Reproducibility of fetal biometry assessment is improved with use of the focus point for plane acquisition, regardless of sonographer experience. We propose that this method should be implemented in clinical practice and training programs in fetal biometry. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Ultrasound Plane Pose Regression: Assessing Generalized Pose Coordinates in the Fetal Brain

In obstetric ultrasound (US) scanning, the learner's ability to mentally build a three-dimensional (3D) map of the fetus from a two-dimensional (2D) US image represents a significant challenge in skill acquisition. We aim to build a US plane localization system for 3D visualization, training, and guidance without integrating additional sensors. This work builds on top of our previous work, which predicts the six-dimensional (6D) pose of arbitrarily oriented US planes slicing the fetal brain with respect to a normalized reference frame using a convolutional neural network (CNN) regression network. Here, we analyze in detail the assumptions of the normalized fetal brain reference frame and quantify its accuracy with respect to the acquisition of transventricular (TV) standard plane (SP) for fetal biometry. We investigate the impact of registration quality in the training and testing data and its subsequent effect on trained models. Finally, we introduce data augmentations and larger training sets that improve the results of our previous work, achieving median errors of 2.97 mm and 6.63° for translation and rotation, respectively.

An evaluation of systematic and random errors in ultrasound estimated fetal weight during serial ultrasound

Introduction

Ultrasound estimated fetal weight is increasingly being used in the monitoring of fetal growth. Large systematic and random errors in estimated fetal weight have been reported; these may have an impact on the accuracy of fetal growth monitoring. The aim of this study was to attempt to evaluate these systematic and random errors by analysis of serial ultrasound data.

Methods

Ultrasound measurements and birthweights were retrospectively collected for 100 unselected patients who had undergone serial ultrasound. Birthweights were used to calculate expected fetal growth trajectories using a method for generating growth charts based on customised birthweights. Estimated fetal weight results were then compared with the expected growth trajectories to evaluate systematic and random differences.

Results

Incomplete measurement sets were excluded, reducing the number of scans to less than three for 13 subjects. A further 17 subjects with suspected pathological growth trajectories were excluded. The final analysis included 70 subjects with a total of 246 scans. The mean difference between estimated fetal weight and expected weight over three to six scans ranged from -17.5% to 38.3% with a mean of 8.4%, representing the systematic difference. The standard deviation of these differences ranged from 0.4% to 21% with a mean of 4.3%, representing random difference.

Conclusion

Systematic and random differences between estimated fetal weight and expected fetal weight are significant and make interpretation of fetal growth difficult. Further improvements to formulae and growth curves are required and audit of fetal measurements is essential to service improvement.

Ultrasound evaluation of normal rhesus macaque fetal biometry and uteroplacental hemodynamics

Nonhuman primates are important preclinical models for translational, reproductive, and developmental science. Clinical evaluation of human fetal development is performed using standard sonographic-derived fetal biometry, assessments of amniotic fluid, and uteroplacental hemodynamics. These noninvasive in utero measurements provide important information regarding fetal growth and pregnancy well-being. Abnormalities in fetal growth, amniotic fluid volume, or placental vascular function are associated with placental insufficiency and adverse perinatal outcomes including stillbirth. The fetal biometric parameters most commonly assessed are biparietal diameter, head circumference, abdominal circumference, and femur diaphysis length. Evaluation of amniotic fluid volume includes measuring the fluid in four quadrants of the uterus to generate an Amniotic Fluid Index. Measures of uteroplacental hemodynamics typically include doppler assessment of the umbilical artery and ductus venosus, but can also include interrogation of the uterine artery and umbilical vein. In this study, we compile prenatal ultrasound data of fetal biometry, amniotic fluid measurements, and uteroplacental hemodynamics obtained from pregnancy studies conducted at the Oregon National Primate Research Center. The data included are from control unperturbed pregnant animals who have not undergone in utero experimental manipulations. This is the first report of comprehensive sonographic measurements following standardized clinical obstetric protocols utilized in rhesus macaques. The outcome is a large, prenatal ultrasound resource to be used by laboratory animal researchers in future nonhuman primate pregnancy studies for antenatal assessment.

Is accuracy of estimated fetal weight improved by better image quality scores?

OBJECTIVE

To assess in a group of ultrasound operators of various levels of experience the predictive value of systematic quality scoring to assess estimated fetal weight (EFW) validity.

METHODS

Screenshots, sonographer experience, and neonate birth weight were collected for 131 ultrasound examinations in the 7 days before birth. The difference (EFW error) between projected birth weight (EFW + [30 g × interval in days to birth]) and actual birth weight was then assessed (absolute value). Three senior sonographers rated all the screenshots (International Society of Ultrasound in Obstetrics and Gynecology 16-point score for image quality) and interobserver reproducibility was assessed concomitantly. The impact of the score on EFW accuracy was then assessed (univariate analysis). Receiver operating characteristic curves allowed us to assess the score's positive predictive value (PPV) for accurate EFW.

RESULTS

Mean birth weight was 2998 ± 954 g and mean EFW error was 8.6% ± 7.1%. Both the sonographer's experience and score significantly impacted the EFW error (P < 0.05). The PPVs of systematic image scores for identifying an EFW error greater than 10% and greater than 15% were appropriate for clinical use (areas under the curve 0.61 and 0.70, respectively). Score reproducibility was modest.

CONCLUSION

Low image scores and limited ultrasound expertise are associated with an increased risk of inaccurate EFW.

Training in Obstetric Ultrasound Biometry: Results from a Multicenter Reproducibility Study

OBJECTIVES

To assess the intra- and interobserver reproducibility of fetal biometry measurements obtained by trainee (junior) and experienced sonographers (senior) in the contest of two training programs in obstetric ultrasound.

METHODS

This was a prospective study on 192 women recruited ensuring an even distribution throughout gestation (18-41 weeks), at University College London Hospital (UCLH), England (87 cases), and at Maternité Regionale Universitaire de Nancy (MRUN), France (105 cases). The training took place in two training centers with experience in ultrasound training and subspecialist training in fetal medicine. Measurements for head circumference (HC), abdominal circumference (AC), and femur length (FL) were obtained twice by junior and senior sonographers, blind to their own and each other's measurements. Differences between and within sonographers were expressed in millimeters and as a percentage of fetal dimensions. Reproducibility was assessed using Bland-Altman plots.

RESULTS

Reproducibility was overall high with 95% confidence intervals (CI) within <6% for intraobserver and <8% for interobserver reproducibility. Intraobserver reproducibility was lower within junior than within senior sonographers' measurements for HC (95% CI: <4% versus <3%) and FL (95% CI: <6% and < 5%). Intraobserver reproducibility was similar between the two centers/training programs (AC 95% CI: <6%). Cumulative interobserver reproducibility in both centers was similar to the reproducibility within a single site (95% CI: <5%, <8%, and <7% for HC, AC, and FL, respectively).

CONCLUSIONS

Reproducibility of fetal biometry measurement was high in centers with structured training programs regardless of sonographers' experience. Reproducibility was higher in sonographers who completed the training.

Second and third trimester estimation of gestational age using ultrasound or maternal symphysis-fundal height measurements: A systematic review

Many vulnerable women seek antenatal care late in pregnancy. How should gestational age be determined? We examine all available studies estimating GA >20 weeks. Ultrasound is much better than fundal height, and using cerebellar measurement appears to be the most accurate.

Linked article: This article is commented on by Philip J. Steer, pp. 1459 in this issue. To view this minicommentary visit https://doi.org/10.1111/1471‐0528.17127 .

Deep learning-based plane pose regression in obstetric ultrasound

Purpose

In obstetric ultrasound (US) scanning, the learner’s ability to mentally build a three-dimensional (3D) map of the fetus from a two-dimensional (2D) US image represents a major challenge in skill acquisition. We aim to build a US plane localisation system for 3D visualisation, training, and guidance without integrating additional sensors.

Methods

We propose a regression convolutional neural network (CNN) using image features to estimate the six-dimensional pose of arbitrarily oriented US planes relative to the fetal brain centre. The network was trained on synthetic images acquired from phantom 3D US volumes and fine-tuned on real scans. Training data was generated by slicing US volumes into imaging planes in Unity at random coordinates and more densely around the standard transventricular (TV) plane.

Results

With phantom data, the median errors are 0.90 mm/1.17\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}∘ and 0.44 mm/1.21\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}∘ for random planes and planes close to the TV one, respectively. With real data, using a different fetus with the same gestational age (GA), these errors are 11.84 mm/25.17\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}∘. The average inference time is 2.97 ms per plane.

Conclusion

The proposed network reliably localises US planes within the fetal brain in phantom data and successfully generalises pose regression for an unseen fetal brain from a similar GA as in training. Future development will expand the prediction to volumes of the whole fetus and assess its potential for vision-based, freehand US-assisted navigation when acquiring standard fetal planes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11548-022-02609-z.

Dispensing of clomiphene citrate to treat infertility: medication supplied and population prevalence of assisted pregnancies and multiple births

OBJECTIVE

To determine the proportion of pregnancies resulting in birth that were conceived with the use of clomiphene citrate (CC) and the frequency of multiple pregnancy.

DESIGN

Whole-of-population cohort study, constructed through data linkage. Comprehensive Australian Government records of dispensed medications were linked to state Perinatal Registry records for all births of at least 20 weeks' gestation.

SETTING

The state of South Australia.

PATIENT(S)

Women who maintained pregnancy for at least 20 weeks and gave birth between July 2003 and December 2015, a total of 150,713 women with 241,561 pregnancies.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Ongoing pregnancy occurring in proximity to CC, defined as dispensing from 90 days before to the end of a conception window derived from newborn date of birth and gestational age.

RESULT(S)

Linkage to dispensed prescription records was achieved for 97.9% of women. Women who conceived with CC tended to be older and socioeconomically advantaged and more likely than other women to have a history of miscarriage. Ongoing pregnancies associated with CC comprised 1.6% of the total; 5.7% were multiple births (mostly twins, 94.6%) compared with 1.5% in the remainder (98.5% twins).

CONCLUSION(S)

In South Australia, 1.6% of pregnancies (1 in 60) of at least 20 weeks' gestation were conceived proximal to CC dispensing. Of these, 5.7% were multiple pregnancies. This takes the proportion of women who achieved an ongoing pregnancy with medical assistance from 4.4%, based on reports from assisted reproductive technology clinics, to 6% in total.

Ultrasound Diagnosis of the Small and Large Fetus

Antenatal imaging is crucial in the management of high-risk pregnancies. Accurate dating relies on acquisition of reliable and reproducible ultrasound images and measurements. Quality image acquisition is necessary for assessing fetal growth and performing Doppler measurements to help diagnose pregnancy complications, stratify risk, and guide management. Further research is needed to ascertain whether current methods for estimating fetal weight can be improved with 3-dimensional ultrasound or magnetic resonance imaging; optimize dating with late initiation of prenatal care; minimize under-diagnosis of fetal growth restriction; and identify the best strategies to make ultrasound more available in low-income and middle-income countries.

The impact of individual sonographer variation on the detection of small for gestational age fetuses using a third trimester growth scan

OBJECTIVES

Detection of small for gestational age (SGA) fetuses in a third trimester ultrasound could be affected by variation in sonographer performance.

METHODS

Retrospective analysis of all singleton, non-anomalous ultrasound examinations between 35⁺⁰ -36⁺⁶ weeks gestation, in a single institution where a universal 36-week scan is offered. Screen positive was defined as estimated fetal weight (EFW) <10th centile; SGA was birthweight <10th centile. Individual sonographers' distributions of head circumference (HC), abdominal circumference (AC) and femur length (FL) were used to assess sonographers' screen positive rate (SPR), detection rate (DR) and true positive rate (TPR). Univariate and multivariate regression analysis was performed to assess the association between the sonographers' mean and SD (SD) for HC, AC, FL and their SPR, DR and TPR.

RESULTS

There were 27 sonographers performing more than 50 examinations per year, a total of 5691 scans. The mean incidence of SGA was 10.0%. For an overall SPR of 9.4%, the overall DR was 43.8% (95% CI: 39.6% - 48.1%) and the overall TPR was 46.5% (95% CI: 42.9% - 50.2%). Higher AC scatter (SD difference up to 11.6 mm) was associated with higher SPR (P = 0.001). Lower mean FL (difference up to 3.6 mm) was associated with higher SPR (P = 0.003) and higher DR (P = 0.002). As a result, DR varied amongst different sonographers between 14.3% and 85.7% and TPR varied between 8.3% and 100.0%.

CONCLUSIONS

Monitoring of individual AC and FL distributions is a simple and effective tool for institutional quality assurance.

Towards automated extraction of 2D standard fetal head planes from 3D ultrasound acquisitions: A clinical evaluation and quality assessment comparison

INTRODUCTION

Clinical evaluation of deep learning (DL) tools is essential to compliment technical accuracy metrics. This study assessed the image quality of standard fetal head planes automatically-extracted from three-dimensional (3D) ultrasound fetal head volumes using a customised DL-algorithm.

METHODS

Two observers retrospectively reviewed standard fetal head planes against pre-defined image quality criteria. Forty-eight images (29 transventricular, 19 transcerebellar) were selected from 91 transabdominal fetal scans (mean gestational age = 26 completed weeks, range = 20+5-32+3 weeks). Each had two-dimensional (2D) manually-acquired (2D-MA), 3D operator-selected (3D-OS) and 3D-DL automatically-acquired (3D-DL) images. The proportion of adequate images from each plane and modality, and the number of inadequate images per plane was compared for each method. Inter and intra-observer agreement of overall image quality was calculated.

RESULTS

Sixty-seven percent of 3D-OS and 3D-DL transventricular planes were adequate quality. Forty-five percent of 3D-OS and 55% of 3D-DL transcerebellar planes were adequate. Seventy-one percent of 3D-OS and 86% of 3D-DL transventricular planes failed with poor visualisation of intra-cranial structures. Eighty-six percent of 3D-OS and 80% of 3D-DL transcerebellar planes failed due to inadequate visualisation of cerebellar hemispheres. Image quality was significantly different between 2D and 3D, however, no significant difference between 3D-modalities was demonstrated (p < 0.005). Inter-observer agreement of transventricular plane adequacy was moderate for both 3D-modalities, and weak for transcerebellar planes.

CONCLUSION

The 3D-DL algorithm can automatically extract standard fetal head planes from 3D-head volumes of comparable quality to operator-selected planes. Image quality in 3D is inferior to corresponding 2D planes, likely due to limitations with 3D-technology and acquisition technique.

IMPLICATIONS FOR PRACTICE

Automated image extraction of standard planes from US-volumes could facilitate use of 3DUS in clinical practice, however image quality is dependent on the volume acquisition technique.

Quality control of fetal biometric evaluation and Doppler ultrasound

In recent years quality control in obstetric ultrasound has become recommended and an essential component of obstetric scanning. This is to minimize the inaccuracy and variability related to fetal measurements, to provide an effective quality assurance system to sonographers to certify their practice and decrease the impact of medical litigations. For a quality control system in obstetric ultrasound to be useful clinically, multiple strategies need to be employed: certified training, practical standardization exercise, image storing, qualitative and quantitative quality control. Qualitative quality control consists of the evaluation of images obtained for fetal biometry and Doppler scans using an objective score against predefined criteria. Quantitative quality control consists of analyzing quantitatively the performance of a sonographer and the impact on measurements values. Quantitative analysis could be performed either using estimates of intraobserver or interobserver reproducibility of plane acquisition and caliper placements.

Fetal cerebellar growth and Sylvian fissure maturation: international standards from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project

OBJECTIVE

To construct international ultrasound-based standards for fetal cerebellar growth and Sylvian fissure maturation.

METHODS

Healthy, well nourished pregnant women, enrolled at < 14 weeks' gestation in the Fetal Growth Longitudinal Study (FGLS) of INTERGROWTH-21^st , an international multicenter, population-based project, underwent serial three-dimensional (3D) fetal ultrasound scans every 5 ± 1 weeks until delivery in study sites located in Brazil, India, Italy, Kenya and the UK. In the present analysis, only those fetuses that underwent developmental assessment at 2 years of age were included. We measured the transcerebellar diameter and assessed Sylvian fissure maturation using two-dimensional ultrasound images extracted from available 3D fetal head volumes. The appropriateness of pooling data from the five sites was assessed using variance component analysis and standardized site differences. For each Sylvian fissure maturation score (left or right side), mean gestational age and 95% CI were calculated. Transcerebellar diameter was modeled using fractional polynomial regression, and goodness of fit was assessed.

RESULTS

Of those children in the original FGLS cohort who had developmental assessment at 2 years of age, 1130 also had an available 3D ultrasound fetal head volume. The sociodemographic characteristics and pregnancy/perinatal outcomes of the study sample confirmed the health and low-risk status of the population studied. In addition, the fetuses had low morbidity and adequate growth and development at 2 years of age. In total, 3016 and 2359 individual volumes were available for transcerebellar-diameter and Sylvian-fissure analysis, respectively. Variance component analysis and standardized site differences showed that the five study populations were sufficiently similar on the basis of predefined criteria for the data to be pooled to produce international standards. A second-degree fractional polynomial provided the best fit for modeling transcerebellar diameter; we then estimated gestational-age-specific 3^rd , 50^th and 97^th smoothed centiles. Goodness-of-fit analysis comparing empirical centiles with smoothed centile curves showed good agreement. The Sylvian fissure increased in maturation with advancing gestation, with complete overlap of the mean gestational age and 95% CIs between the sexes for each development score. No differences in Sylvian fissure maturation between the right and left hemispheres were observed.

CONCLUSION

We present, for the first time, international standards for fetal cerebellar growth and Sylvian fissure maturation throughout pregnancy based on a healthy fetal population that exhibited adequate growth and development at 2 years of age. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Fetal biometry in ultrasound: A new approach to assess the long-term impact of simulation on learning patterns

CONTEXT

Simulation-based education (SBE) has demonstrated its acceptability and effectiveness in improving ultrasound training. Because of the high cost of its implementation (investment in equipment and supervision), a pragmatic assessment of the transfer of skills learned in SBE to clinical practice and the identification of its optimal scheduling conditions have been requested to optimize its input.

OBJECTIVES

To quantify the long-term impact of simulation-based education (SBE) on the adequate performance of ultrasound fetal biometry measurements (I). The secondary objective was to identify the temporal patterns that enhanced SBE input in learning (II).

METHODS

Trainees were arbitrarily assigned to a 6-month course in obstetric ultrasound with or without an SBE workshop. In the SBE group, the workshop was implemented 'before' or at an 'early' or a 'late-stage' of the course. Those who did not receive SBE were the control group. The ultrasound skills of all trainees were prospectively collected, evaluated by calculating the delta between OSAUS (Objective Structured Assessment of Ultrasound Skills) scores before and after the course (I). Concomitantly, the accuracy of trainees' measurements was assessed throughout the course by verifying their correlation with the corresponding measurements by their supervisors. The percentage of trainees able to perform five consecutive sets of correct measurements in the control group and in each SBE subgroup were compared (II).

RESULTS

The study included 61 trainees (39 SBE and 22 controls). Comparisons between groups showed no significant difference in the quantitative assessment of skill enhancement (difference in the pre- and post-internship OSAUS score: 1.09 ± 0.87 in the SBE group and 0.72 ± 0.98 in the control group) (I). Conversely, the predefined acceptable skill level was reached by a significantly higher proportion of trainees in the 'early' SBE subgroup (74%, compared with 30% in the control group, P<0.01)(II).

CONCLUSIONS

The quantitative assessment does not support the existence of long-term benefits from SBE training, although the qualitative assessment confirmed SBE helped to raise the minimal level within a group when embedded in an 'early' stage of a practical course.

The impact of optimal dating on the assessment of fetal growth

BACKGROUND

The impact of using the Intergrowth (IG) dating formulae in comparison to the commonly used Robinson dating on the evaluation of biometrics and estimated fetal weight (EFW) has not been evaluated.

METHODS

Nationwide cross-sectional study of routine fetal ultrasound biometry in low-risk pregnant women whose gestational age (GA) had been previously assessed by a first trimester CRL measurement. We compared the CRL-based GA according to the Robinson formula and the IG formula. We evaluated the fetal biometric measurements as well as the EFW taken later in pregnancy depending on the dating formula used. Mean and standard deviation of the Z scores as well as the number and percentage of cases classified as <3rd, < 10th, >90th and > 97th percentile were compared.

RESULTS

Three thousand five hundred twenty-two low-risk women with scans carried out after 18 weeks were included. There were differences of zero, one and 2 days in 642 (18.2%), 2700 (76.7%) and 180 (5%) when GA was estimated based on the Robinson or the IG formula, respectively. The biometry Z scores assessed later in pregnancy were all statistically significantly lower when the Intergrowth-based dating formula was used (p < 10- 4). Likewise, the number and percentage of foetuses classified as <3rd, < 10th, >90th and > 97th percentile demonstrated significant differences. As an example, the proportion of SGA foetuses varied from 3.46 to 4.57% (p = 0.02) and that of LGA foetuses from 17.86 to 13.4% (p < 10- 4).

CONCLUSION

The dating formula used has a quite significant impact on the subsequent evaluation of biometry and EFW. We suggest that the combined and homogeneous use of a recent dating standard, together with prescriptive growth standards established on the same low-risk pregnancies, allows an optimal assessment of fetal growth.

Fetal growth velocity standards from the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project

BACKGROUND

Human growth is susceptible to damage from insults, particularly during periods of rapid growth. Identifying those periods and the normative limits that are compatible with adequate growth and development are the first key steps toward preventing impaired growth.

OBJECTIVE

This study aimed to construct international fetal growth velocity increment and conditional velocity standards from 14 to 40 weeks' gestation based on the same cohort that contributed to the INTERGROWTH-21st Fetal Growth Standards.

STUDY DESIGN

This study was a prospective, longitudinal study of 4321 low-risk pregnancies from 8 geographically diverse populations in the INTERGROWTH-21st Project with rigorous standardization of all study procedures, equipment, and measurements that were performed by trained ultrasonographers. Gestational age was accurately determined clinically and confirmed by ultrasound measurement of crown-rump length at <14 weeks' gestation. Thereafter, the ultrasonographers, who were masked to the values, measured the fetal head circumference, biparietal diameter, occipitofrontal diameter, abdominal circumference, and femur length in triplicate every 5 weeks (within 1 week either side) using identical ultrasound equipment at each site (4-7 scans per pregnancy). Velocity increments across a range of intervals between measures were modeled using fractional polynomial regression.

RESULTS

Peak velocity was observed at a similar gestational age: 16 and 17 weeks' gestation for head circumference (12.2 mm/wk), and 16 weeks' gestation for abdominal circumference (11.8 mm/wk) and femur length (3.2 mm/wk). However, velocity growth slowed down rapidly for head circumference, biparietal diameter, occipitofrontal diameter, and femur length, with an almost linear reduction toward term that was more marked for femur length. Conversely, abdominal circumference velocity remained relatively steady throughout pregnancy. The change in velocity with gestational age was more evident for head circumference, biparietal diameter, occipitofrontal diameter, and femur length than for abdominal circumference when the change was expressed as a percentage of fetal size at 40 weeks' gestation. We have also shown how to obtain accurate conditional fetal velocity based on our previous methodological work.

CONCLUSION

The fetal skeleton and abdomen have different velocity growth patterns during intrauterine life. Accordingly, we have produced international Fetal Growth Velocity Increment Standards to complement the INTERGROWTH-21st Fetal Growth Standards so as to monitor fetal well-being comprehensively worldwide. Fetal growth velocity curves may be valuable if one wants to study the pathophysiology of fetal growth. We provide an application that can be used easily in clinical practice to evaluate changes in fetal size as conditional velocity for a more refined assessment of fetal growth than is possible at present (https://lxiao5.shinyapps.io/fetal_growth/). The application is freely available with the other INTERGROWTH-21st tools at https://intergrowth21.tghn.org/standards-tools/.

Training the trainees: a pilot study of inter-observer discrepancy and learning curve in the maternal foetal unit of a tertiary centre

Our study aims to present the preliminary findings of an ongoing prospective cohort study that assesses the trainees' ability to perform foetal biometry during the third trimester of pregnancy. Sixty-three women with third-trimester singleton pregnancies were included. A biometry scan was performed byboth residents and a foetal medicine specialist in the Third department of Obstetrics and Gynaecology of Attikon University Hospital. For each case, the ultrasonographic measurements of the two operator groups were compared. The mean difference of the resident group compared to the specialist group was: for the biparietal diameter +1.3 mm (CI 95%, range -10.6 to +13,3, ±1.96 SD), for the occipitofrontal diameter -2.6 mm (CI 95%, range -31.5 to +26.2), for the anterior-posterior abdominal diameter -2.6 mm (CI 95%, range -17.9 to +12.8), for the transverse abdominal diameter -0.7 mm (CI 95%, range -17.1 to +15.7) and for the femur length -1.1 mm (CI 95%, range -11.7 to +9.6). We observed that, among all biometric parameters, the most accurate -based on the specialist group were the head circumference measurements. The highest discrepancy was noted for the abdominal assessment. Given that foetal biometry is of utmost importance in obstetrical clinical evaluation and management, a study that highlights the weaknesses of residents in this field could open new horizons in optimising the learning procedure.Impact statementWhat is already known on this subject? After review of the literature, we found only a few studies on inter- and intra-observer discrepancy in foetal biometry measurements among specialists.What the results of this study add? To our knowledge, our study is the first to evaluate residents' capacity of performing a biometry scan, by comparing their measurements to those of MFM specialists.What the implications are of these findings to clinical practice and/or further research? The need for constant evaluation of residents is indisputable. Our study could help to improve their ultrasound skills by giving emphasis on residents' weaknesses. With further research on this subject, a standard system of evaluation could be formed and determine the duration and type of training required for each resident.

Quality assessment of ultrasonic foetal biometry during the IUGR Risk Selection (IRIS) trial: A cross sectional study

OBJECTIVE

Intrauterine growth restriction is a major risk factor for perinatal morbidity and mortality. Ultrasonic foetal biometry is an important tool to monitor foetal growth. Therefore, the quality of these biometry scans is vital to achieve good diagnostic accuracy. We assessed the quality of foetal biometry during a nationwide trial and explored its association with sonographer's characteristics.

METHODS

Four scans from every sonographer (n = 154), performed at 29 and 35 weeks gestational age were collected. Two assessors scored these scans according to a national audit system. A quality score ≥ 65% was considered 'adequate'. We compared the quality scores per scoring criterion (i.e. foetal head measurements, abdominal circumference and femur length with regard to magnification, correctness of the plane and calliper placement) and gestational age. We analysed the associations between characteristics of the sonographers and their scores. In a subsample of scans of 30 sonographers we determined the interrater agreement on the quality scores given by the two assessors independently.

FINDINGS

The mean score was 81.3%. Thirteen sonographers (8.4%) failed to achieve 'adequate quality'. Scores for femur length (83.8%) were significantly higher than those for head (77.9%) and abdominal circumference (78.6%) (both P < 0.05). Scores for correctness of the plane (73.4%) were lower than those for magnification (81.2%) and calliper placement (85.7%) (both P < 0.05). Gestational age did not affect the quality scores. Only the number of scans performed in the previous year was positively associated with the scores (β = 0.01; P < 0.05). The mean interrater difference in quality scoring was 11.1%, with 77.6% agreement on scans of 'adequate quality', but with no agreement on scans with 'insufficient quality'.

KEY CONCLUSIONS AND IMPLICATIONS FOR PRACTICE

Most sonographers achieved an 'adequate quality' score. Highest quality scores were attained for femur length, lowest quality scores for the correct plane. The number of scans one performs is associated with the quality scores, yet the minimum number of scans to perform for guaranteed quality still needs to be determined. Further research is needed to develop a standardized method to assess and maintain good ultrasonic foetal biometry quality.

Caveats in the monitoring of fetal growth using ultrasound estimated fetal weight

Introduction

Ultrasound estimated fetal weight is increasingly being used in the monitoring of fetal growth. Differences between estimated fetal weight formulae, curves and measurement methods could lead to significant differences in results. The aim of this study was to investigate the potential impact of these differences on estimated fetal weight and its use in monitoring fetal growth, both by modelling and by analysis of ultrasound scan data.

Methods

Four estimated fetal weight curves were compared in their original form and also normalised to term weight. Estimated fetal weight was calculated from 50th centiles of widely used charts of abdominal and head circumference and femur length and plotted on a widely used estimated fetal weight curve. Fetal measurement data were used to assess the impact of fetal proportions on estimated fetal weight error and on growth trajectory when different estimated fetal weight formulae are used.

Results

Estimated fetal weight curves differ significantly, but after normalisation there is closer agreement. Estimated fetal weight modelled using modern measurement methods differs from the widely used estimated fetal weight growth curve. Errors in estimated fetal weight are correlated with differences in fetal proportions and this can lead to significant changes in estimated fetal weight growth trajectory if different estimated fetal weight formulae are used.

Conclusions

Choice of measurement methods, estimated fetal weight formulae and growth curves have a significant effect on estimated fetal weight growth trajectories relative to normal ranges. It is important to understand these caveats when using estimated fetal weight to monitor fetal growth.

International standards for fetal brain structures based on serial ultrasound measurements from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project

OBJECTIVE

To create prescriptive growth standards for five fetal brain structures, measured using ultrasound, in healthy, well-nourished women at low risk of impaired fetal growth and poor perinatal outcome, taking part in the Fetal Growth Longitudinal Study (FGLS) of the INTERGROWTH-21^st Project.

METHODS

This was a complementary analysis of a large, population-based, multicenter, longitudinal study. The sample analyzed was selected randomly from the overall FGLS population, ensuring an equal distribution among the eight diverse participating sites and of three-dimensional (3D) ultrasound volumes across pregnancy (range: 15-36 weeks' gestation). We measured, in planes reconstructed from 3D ultrasound volumes of the fetal head at different timepoints in pregnancy, the size of the parieto-occipital fissure (POF), Sylvian fissure (SF), anterior horn of the lateral ventricle, atrium of the posterior horn of the lateral ventricle (PV) and cisterna magna (CM). Fractional polynomials were used to construct the standards. Growth and development of the infants were assessed at 1 and 2 years of age to confirm their adequacy for constructing international standards.

RESULTS

From the entire FGLS cohort of 4321 women, 451 (10.4%) were selected at random. After exclusions, 3D ultrasound volumes from 442 fetuses born without a congenital malformation were used to create the charts. The fetal brain structures of interest were identified in 90% of cases. All structures, except the PV, showed increasing size with gestational age, and the size of the POF, SF, PV and CM showed increasing variability. The 3^rd , 5^th , 50^th , 95^th and 97^th smoothed centiles are presented. The 5^th centiles for the POF and SF were 3.1 mm and 4.7 mm at 22 weeks' gestation and 4.6 mm and 9.9 mm at 32 weeks, respectively. The 95^th centiles for the PV and CM were 8.5 mm and 7.5 mm at 22 weeks and 8.6 mm and 9.5 mm at 32 weeks, respectively.

CONCLUSIONS

We have produced prescriptive size standards for fetal brain structures based on prospectively enrolled pregnancies at low risk of abnormal outcome. We recommend these as international standards for the assessment of measurements obtained using ultrasound from fetal brain structures. © 2020 Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Accuracy of sonographic estimation of weight in fetuses with abdominal wall defects

BACKGROUND

Accurate estimation of fetal weight is essential in guiding management of fetuses with abdominal wall defects (AWDs), as growth restriction is an important predictor of perinatal morbidity and mortality. Several sonographic formulae are available involving multiple biometric parameters, but abdominal circumference measurements may underestimate weight in fetuses with AWDs. No formula has yet shown superior accuracy.

AIMS

The objectives of this study were to evaluate, in fetuses with gastroschisis and omphalocoele, the accuracy of a sonographic estimated fetal weight (EFW) formula proposed by Siemer and colleagues, specifically for use in fetuses with AWDs compared to the commonly used Hadlock IV formula in estimating fetal weight, and detecting small for gestational age (SGA) fetuses.

MATERIALS AND METHODS

A retrospective cohort of 113 fetuses with AWDs was identified from an Australian teaching hospital over 13 years. Pregnancy data and sonographic fetal biometry parameters were obtained. The accuracy of each formula in predicting birthweight was compared using Bland-Altman limits of agreement, and the intraclass correlation coefficient between EFW and actual birthweight. Performance of each formula in detecting SGA fetuses was determined.

RESULTS

The Siemer and Hadlock formulae have similar accuracies for predicting birthweight in fetuses with AWDs. The Hadlock formula has a higher detection rate for SGA < 10^th centile and < 3^rd centile compared to the Seimer formula (84% vs 68% and 83% vs 67% respectively), albeit with a higher false-positive rate.

CONCLUSION

There is no clear clinical advantage in using the Siemer formula, which is specifically designed for fetuses with AWDs, over the Hadlock formula to estimate weight in fetuses with AWDs.

Prospective assessment of reproducibility of three-dimensional ultrasound for fetal biometry

PURPOSE

To compare fetal ultrasound measurements performed by two observers with different levels of experience and evaluate the potential contribution of the use of three-dimensional (3D) ultrasound on repeatability, reproducibility and agreement of two-dimensional (2D) and 3D-derived measurements.

MATERIALS AND METHODS

Two observers (one senior and one junior) measured head circumference (HC), abdominal circumference (AC) and femur length (FL) in 33 fetuses (20 to 40 weeks of gestation). Each observer performed two series of 2D measurements and two series of 3D measurements (i.e., measurements derived from triplane volume processing). Measurements were converted into Z-scores according to gestational age. Variability between the different series of measurements was studied using Bland-Altmann plots and intra-class correlation coefficients (ICC).

RESULTS

Agreement with the 2D measurements of the senior observer was higher in 3D than in 2D for the junior observer (systematic differences of -0.4, -0.2 and -0.8 Z-score vs. -0.1, -0.1 and -0.6 for HC, AC and FL on 2D and 3D datasets, respectively). The use of 3D ultrasound improved junior observer repeatability (ICC=0.94, 0.88, 0.90 vs. 0.94, 0.94 and 0.96 for HC, AC and FL in 2D and 3D, respectively). The reproducibility was greater using the junior observer 3D datasets (ICC=0.75, 0.60 and 0.45 vs. 0.79, 0.89 and 0.63 for HC, AC and FL, respectively).

CONCLUSION

The use of 3D ultrasound improves the consistency of the measurements performed by a junior observer and increases the overall repeatability and reproducibility of measurements performed by observers with different levels of experience.

Staging achilles tendinopathy using ultrasound imaging: the development and investigation of a new ultrasound imaging criteria based on the continuum model of tendon pathology

Aim

To develop a standardised ultrasound imaging (USI)-based criteria for the diagnosis of tendinopathy that aligns with the continuum model of tendon pathology. Secondary aims were to assess both the intra-rater and inter-rater reliability of the criteria.

Methods

A criteria was developed following a face validity assessment and a total of 31 Achilles tendon ultrasound images were analysed. Intra-rater and inter-rater reliability were assessed for overall tendinopathy stage (normal, reactive/early dysrepair or late dysrepair/degenerative) as well as for individual parameters (thickness, echogenicity and vascularity). Quadratic weighted kappa (k_w) was used to report on reliability.

Results

Intra-rater reliability was ‘substantial’ for overall tendinopathy staging (k_w rater A; 0.77, 95% CI 0.59 to 0.94, rater B; 0.70, 95% CI 0.52 to 0.89) and ranged from ‘substantial’ to ‘almost perfect’ for thickness (k_w rater A; 0.75, 95% CI 0.59 to 0.90, rater B; 0.84, 95% CI 0.71 to 0.98), echogenicity (k_w rater A; 0.78, 95% CI 0.62 to 0.95, rater B; 0.73, 95% CI 0.58 to 0.89) and vascularity (k_w rater A; 0.86, 95% CI 0.74 to 0.98, rater B; 0.89, 95% CI 0.79 to 0.99). Inter-rater reliability ranged from ‘substantial’ to ‘almost perfect’ for overall tendinopathy staging (k_w round 1; 0.75, 95% CI 0.58 to 0.91, round 2; 0.81, 95% CI 0.63 to 0.99), thickness (k_w round 1; 0.65, 95% CI 0.48 to 0.83, round 2; 0.77, 95% CI 0.60 to 0.93), echogenicity (k_w round 1; 0.70, 95% CI 0.54 to 0.85, round 2; 0.76, 95% CI 0.58 to 0.94) and vascularity (k_w round 1; 0.89, 95% CI 0.79 to 0.99, round 2; 0.86, 95% CI 0.74 to 0.98). Inter-rater reliability increased from ‘substantial’ in round 1 (k_w 0.75, 95% CI 0.58 to 0.91) to ‘almost perfect’ in round 2 (0.81, 95% CI 0.63 to 0.99).

Conclusion

Intra-rater and inter-rater reliability were ‘substantial’ to ‘almost perfect’ when utilising an USI-based criteria to diagnose Achilles tendinopathy. This is the first study to use the continuum model of tendon pathology to develop an USI-based criteria to diagnose tendinopathy.

Toward point-of-care ultrasound estimation of fetal gestational age from the trans-cerebellar diameter using CNN-based ultrasound image analysis

Obstetric ultrasound is a fundamental ingredient of modern prenatal care with many applications including accurate dating of a pregnancy, identifying pregnancy-related complications, and diagnosis of fetal abnormalities. However, despite its many benefits, two factors currently prevent wide-scale uptake of this technology for point-of-care clinical decision-making in low- and middle-income country (LMIC) settings. First, there is a steep learning curve for scan proficiency, and second, there has been a lack of easy-to-use, affordable, and portable ultrasound devices. We introduce a framework toward addressing these barriers, enabled by recent advances in machine learning applied to medical imaging. The framework is designed to be realizable as a point-of-care ultrasound (POCUS) solution with an affordable wireless ultrasound probe, a smartphone or tablet, and automated machine-learning-based image processing. Specifically, we propose a machine-learning-based algorithm pipeline designed to automatically estimate the gestational age of a fetus from a short fetal ultrasound scan. We present proof-of-concept evaluation of accuracy of the key image analysis algorithms for automatic head transcerebellar plane detection, automatic transcerebellar diameter measurement, and estimation of gestational age on conventional ultrasound data simulating the POCUS task and discuss next steps toward translation via a first application on clinical ultrasound video from a low-cost ultrasound probe.

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.

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

OBJECTIVE

To assess studies reporting reference ranges for umbilical artery (UA) and fetal middle cerebral artery (MCA) Doppler indices and cerebroplacental ratio (CPR), using a set of predefined methodological quality criteria for study design, statistical analysis and reporting methods.

METHODS

This was a systematic review of observational studies in which the primary aim was to create reference ranges for UA and MCA Doppler indices and CPR in fetuses of singleton gestations. A search for relevant articles was performed in MEDLINE, EMBASE, CINAHL, Web of Science (from inception to 31 December 2016) and references of the retrieved articles. Two authors independently selected studies, assessed the risk of bias and extracted the data. Studies were scored against a predefined set of independently agreed methodological criteria and an overall quality score was assigned to each study. Linear multiple regression analysis assessing the association between quality scores and study characteristics was performed.

RESULTS

Thirty-eight studies met the inclusion criteria. The highest potential for bias was noted in the following fields: 'ultrasound quality control measures', in which only two studies demonstrated a comprehensive quality-control strategy; 'number of measurements taken for each Doppler variable', which was apparent in only three studies; 'sonographer experience', in which no study on CPR reported clearly the experience or training of the sonographers, while only three studies on UA Doppler and four on MCA Doppler did; and 'blinding of measurements', in which only one study, on UA Doppler, reported that sonographers were blinded to the measurement recorded during the examination. Sample size estimations were present in only seven studies. No predictors of quality were found on multiple regression analysis. Reference ranges varied significantly with important clinical implications for what is considered normal or abnormal, even when restricting the analysis to the highest scoring studies.

CONCLUSIONS

There is considerable methodological heterogeneity in studies reporting reference ranges for UA and MCA Doppler indices and CPR, and the resulting references have important implications for clinical practice. There is a need for the standardization of methodologies for Doppler velocimetry and for the development of reference standards, which can be correctly interpreted and applied in clinical practice. We propose a set of recommendations for this purpose. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Are ultrasound foetal circumference measurement methods interchangeable?

A variety of methods is available for the ultrasound measurement of foetal circumferences; ellipse fitting and derived measurements are often used interchangeably based on an assumption of equivalence, despite evidence that results may differ. The aim of this study was to investigate the differences between ellipse fitting and derived circumferences in clinical practice. Head and abdominal circumferences originally measured using ellipse fitting were retrospectively derived from anterior-posterior and transverse diameters using a widely used formula. Where the necessary measurements were available, foetal weight was estimated. Differences between ellipse fitted and derived measurements were compared using Bland-Altman plots. Images from 65 patients (gestational age 20 to 40 weeks) were collected; four head circumference and five abdominal circumference images were excluded due to poor image quality. Data were available for estimated foetal weight calculation for 48 patients. There were small systematic differences between ellipse fitted and derived measurements. Random differences varied between 20 week scans, early growth scans and later growth scans, so were analysed in these three groups. The 95% confidence intervals were ±6 mm (±3%), ±7 mm (±2%) and ±20 mm (±6%) for head circumference at 20 weeks, earlier growth scans and later scans, respectively; the 95% confidence intervals for abdominal circumference were ±7 mm (±5%), ±11 mm (±5%) and ±17 mm (±6%) and for estimated foetal weight were ±23 g (±6%), ±69 g (±5%) and ±311 g (±12%). Foetal circumference measurement methods are not interchangeable. The derived method should be used where size, growth and estimated foetal weight charts are based on this method.

Deep clinical and biological phenotyping of the preterm birth and small for gestational age syndromes: The INTERBIO-21 st Newborn Case-Control Study protocol

Background: INTERBIO-21 ^st is Phase II of the INTERGROWTH-21 ^st Project, the population-based, research initiative involving nearly 70,000 mothers and babies worldwide coordinated by Oxford University and performed by a multidisciplinary network of more than 400 healthcare professionals and scientists from 35 institutions in 21 countries worldwide. Phase I, conducted 2008-2015, consisted of nine complementary studies designed to describe optimal human growth and neurodevelopment, based conceptually on the WHO prescriptive approach. The studies generated a set of international standards for monitoring growth and neurodevelopment, which complement the existing WHO Child Growth Standards. Phase II aims to improve the functional classification of the highly heterogenous preterm birth and fetal growth restriction syndromes through a better understanding of how environmental exposures, clinical conditions and nutrition influence patterns of human growth from conception to childhood, as well as specific neurodevelopmental domains and associated behaviors at 2 years of age.

Methods: In the INTERBIO-21 ^st Newborn Case-Control Study, a major component of Phase II, our objective is to investigate the mechanisms potentially responsible for preterm birth and small for gestational age and their interactions, using deep phenotyping of clinical, growth and epidemiological data and associated nutritional, biochemical, omic and histological profiles. Here we describe the study sites, population characteristics, study design, methodology and standardization procedures for the collection of longitudinal clinical data and biological samples (maternal blood, umbilical cord blood, placental tissue, maternal feces and infant buccal swabs) for the study that was conducted between 2012 and 2018 in Brazil, Kenya, Pakistan, South Africa, Thailand and the UK.

Discussion: Our study provides a unique resource for the planned analyses given the range of potentially disadvantageous exposures (including poor nutrition, pregnancy complications and infections) in geographically diverse populations worldwide. The study should enhance current medical knowledge and provide new insights into environmental influences on human growth and neurodevelopment.

Deep clinical and biological phenotyping of the preterm birth and small for gestational age syndromes: The INTERBIO-21 st Newborn Case-Control Study protocol

Background: INTERBIO-21 ^st is Phase II of the INTERGROWTH-21 ^st Project, the population-based, research initiative involving nearly 70,000 mothers and babies worldwide coordinated by Oxford University and performed by a multidisciplinary network of more than 400 healthcare professionals and scientists from 35 institutions in 21 countries worldwide. Phase I, conducted 2008-2015, consisted of nine complementary studies designed to describe optimal human growth and neurodevelopment, based conceptually on the WHO prescriptive approach. The studies generated a set of international standards for monitoring growth and neurodevelopment, which complement the existing WHO Child Growth Standards. Phase II aims to improve the functional classification of the highly heterogenous preterm birth and fetal growth restriction syndromes through a better understanding of how environmental exposures, clinical conditions and nutrition influence patterns of human growth from conception to childhood, as well as specific neurodevelopmental domains and associated behaviors at 2 years of age. Methods: In the INTERBIO-21 ^st Newborn Case-Control Study, a major component of Phase II, our objective is to investigate the mechanisms potentially responsible for preterm birth and small for gestational age and their interactions, using deep phenotyping of clinical, growth and epidemiological data and associated nutritional, biochemical, omic and histological profiles. Here we describe the study sites, population characteristics, study design, methodology and standardization procedures for the collection of longitudinal clinical data and biological samples (maternal blood, umbilical cord blood, placental tissue, maternal feces and infant buccal swabs) for the study that was conducted between 2012 and 2018 in Brazil, Kenya, Pakistan, South Africa, Thailand and the UK. Discussion: Our study provides a unique resource for the planned analyses given the range of potentially disadvantageous exposures (including poor nutrition, pregnancy complications and infections) in geographically diverse populations worldwide. The study should enhance current medical knowledge and provide new insights into environmental influences on human growth and neurodevelopment.

Design and other methodological considerations for the construction of human fetal and neonatal size and growth charts

This paper discusses the features of study design and methodological considerations for constructing reference centile charts for attained size, growth, and velocity charts with a focus on human growth charts used during pregnancy. Recent systematic reviews of pregnancy dating, fetal size, and newborn size charts showed that many studies aimed at constructing charts are still conducted poorly. Important design features such as inclusion and exclusion criteria, ultrasound quality control measures, sample size determination, anthropometric evaluation, gestational age estimation, assessment of outliers, and chart presentation are seldom well addressed, considered, or reported. Many of these charts are in clinical use today and directly affect the identification of at‐risk newborns that require treatment and nutritional strategies.

This paper therefore reiterates some of the concepts previously identified as important for growth studies, focusing on considerations and concepts related to study design, sample size, and methodological considerations with an aim of obtaining valid reference or standard centile charts. We discuss some of the key issues and provide more details and practical examples based on our experiences from the INTERGROWTH‐21^st Project. We discuss the statistical methodology and analyses for cross‐sectional studies and longitudinal studies in a separate article in this issue.

An objective scoring method to evaluate image quality of middle cerebral artery Doppler

Objective: To validate an objective scoring system for middle cerebral artery (MCA) pulsed wave Doppler images.Method: From an image database of routine 36-week scans, a random sample of MCA Doppler images was selected. Two reviewers rated the images subjectively as acceptable or unacceptable. Subsequently they used an objective 6-point image scoring system and awarded one point for each of the following: (1) anatomical site, (2) magnification, (3) angle of insonation, (4) image clarity, (5) sweep speed adjustment, and (6) velocity scale and baseline adjustment. Image scores 4-6 were defined as good quality whereas 0-3 as poor. The subjective and objective agreement between the two reviewers was compared using the adjusted Kappa statistic.Results: A total of 124 images were assessed. Using objective scoring the agreement rate between reviewers increased to 91.9% (κ = 0.839) compared to subjective agreement 75.8% (κ = 0.516). The agreement for each criterion was: anatomical site 91.1% (κ = 0.823), magnification 95.2% (κ = 0.903), clarity 83.9% (κ = 0.677), angle 96.0% (κ = 0.919), sweep speed 98.4% (κ = 0.968), and velocity scale and baseline 94.4% (κ = 0.887).Conclusion: Objective assessment of MCA Doppler images using a 6-point scoring system has greater interobserver agreement than subjective assessment and could be used for MCA Doppler quality assurance.

Quality control of ultrasound for fetal biometry: results from the INTERGROWTH-21st Project

OBJECTIVE

To assess a comprehensive package of ultrasound quality control in the Fetal Growth Longitudinal Study of the INTERGROWTH-21^st Project, a large multicenter study of fetal growth.

METHODS

Quality control (QC) measures were performed for 20 313 ultrasound scan images obtained prospectively from 4321 fetuses at 14-41 weeks' gestation in eight geographical locations. At the time of each ultrasound examination, three fetal biometric variables (head circumference (HC), abdominal circumference (AC) and femur length (FL)) were measured in triplicate on separately generated images. All measurements were taken in a blinded fashion. QC had two elements: (1) qualitative QC: visual assessment by sonographers at each study site of their images based on specific criteria, with 10% of images being re-assessed at the Oxford-based Ultrasound Quality Unit (compared using an adjusted kappa statistic); and (2) quantitative QC: assessment of measurement data by comparing the first, second and third measurements (intraobserver variability), remeasurement of caliper replacement in 10% (interobserver variability), both by Bland-Altman plots and plotting frequency histograms of the SD of triplicate measurements and assessing how many were above or below 2 SD of the expected distribution. The system allowed the sonographers' performances to be monitored regularly.

RESULTS

A high level of agreement between self- and external scoring was demonstrated for all measurements (κ = 0.99 (95% CI, 0.98-0.99) for HC, 0.98 (95% CI, 0.97-0.99) for AC and 0.96 (95% CI, 0.95-0.98) for FL). Intraobserver 95% limits of agreement (LoA) of ultrasound measures for HC, AC and FL were ± 3.3%, ± 5.6% and ± 6.2%, respectively; the corresponding values for interobserver LoA were ± 4.4%, ± 6.0% and ± 5.6%. The SD distribution of triplicate measurements for all biometric variables showed excessive variability for three of 31 sonographers, allowing prompt identification and retraining.

CONCLUSIONS

Qualitative and quantitative QC monitoring was feasible and highly reproducible in a large multicenter research study, which facilitated the production of high-quality ultrasound images. We recommend that the QC system we developed is implemented in future research studies and clinical practice. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Improving precision of second-trimester biometry

OBJECTIVE

To utilise image score-based criteria for second-trimester fetal biometry as an educational tool to improve biometry quality.

METHODS

Five sonographers regularly performing obstetric ultrasound examinations were recruited for this study. Biometry images were collected from fifteen second-trimester examinations for each sonographer prior to participating in a biometry education session, and another set of biometry images were collected from fifteen second-trimester examinations following the education session. The education session was a one-hour presentation that explained image score-based criteria to evaluate and grade the quality of the bi-parietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL) and humeral length (HL) biometry parameters. Each of the five sonographers performed a total of 30 examinations (15 pre- and 15 post-education session). From these examinations, a total of 150 images were collected for each biometry parameter (75 pre- and 75 post-education). A total of 600 biometry images were evaluated. Images from both the pre- and post-education session were assessed by an obstetrician sonologist using the same image score-based criteria. Pre- and post-image scores were compared using paired t-tests.

RESULTS

Improvement in the mean image scores for all biometry parameters was observed after the education session. The difference between pre- and post-education image quality scores was significant for the AC (P = 0.01), FL (P = 0.002) and for the overall score (P = 0.001).

CONCLUSION

Implementing an image score-based criteria evaluation technique is a simple and useful method to improve fetal biometry precision.

Study on the cephalopelvic relationship with cephalic presentation in nulliparous full-term Chinese pregnant women by MRI with three-dimensional reconstruction

PURPOSE

To analyze the relationship between fetal head size and maternal pelvis size using magnetic resonance imaging (MRI) with a 3-D reconstruction technique.

METHODS

A total of 301 nulliparous full-term Chinese pregnant women with cephalic presentation were enrolled and received MRI examinations before labor onset. Data were collected and imported into Mimics software to reconstruct the maternal pelvis and fetus.

RESULTS

Of 301 pregnant women, 212 underwent vaginal delivery and 32 received cesarean section. The body mass index (BMI) was significantly different between the vaginal delivery group and the suspected cephalopelvic disproportion (CPD) group; the larger the BMI, the higher was the risk of CPD. The transverse diameter of the pelvic inlet and the posterior sagittal diameter of the midpelvis were significantly larger in the vaginal delivery group, compared with the suspected CPD group. Fetal weight > 3.5 kg could be used as a diagnostic indicator for CPD.

CONCLUSIONS

BMI is a risk factor for CPD, and fetal weight < 3.5 kg is an important diagnostic indicator for natural delivery in Chinese pregnant women.

The INTERGROWTH-21st fetal growth standards: toward the global integration of pregnancy and pediatric care

The purpose of the INTERGROWTH-21^st project was to develop international, prescriptive standards for fetal growth assessed by ultrasound and fundal height, preterm postnatal growth, newborn size and body composition, maternal weight gain, and infant development at the age of 2 years. Hence, we have produced, based on World Health Organization recommendations, the first comprehensive set of international standards of optimal fetal and newborn growth that perfectly match the existing World Health Organization child growth standards. Uniquely, the same population was followed up longitudinally from 9 weeks of fetal life to 2 years of age, with growth, health, and nutritional status assessment at 2 years supporting the appropriateness of the population for construction of growth standards. The resulting package of clinical tools allows, for the first time, growth and development to be monitored from early pregnancy to infancy. The INTERGROWTH-21^st fetal growth standards, which are based on observing >4500 healthy pregnancies, nested in a study of >59,000 pregnancies from populations with low rates of adverse perinatal outcomes, show how fetuses should grow-rather than the more limited objective of past references, which describe how they have grown at specific times and locations. Our work has confirmed the fundamental biological principle that variation in human growth across different populations is mostly dependent on environmental, nutritional, and socioeconomic factors. We found that when mothers' nutritional and health needs are met and there are few environmental constraints on growth, <3.5% of the total variability of skeletal growth was due to differences between populations. We propose that not recognizing the concept of optimal growth could deprive the most vulnerable mothers and their babies of optimal care, because local growth charts normalize those at highest risk for growth restriction and overweight, and can be valuable for policymakers to ensure rigorous evaluation and effective resource allocation. We strongly encourage colleagues to join efforts to provide integrated, evidence-based growth monitoring to pregnant women and their infants worldwide. Presently, there are 23.3 million infants born small for gestational age in low- to middle-income countries according to the INTERGROWTH-21^st newborn size standards. We suggest that misclassification of these infants by using local charts could affect the delivery of optimal health care.

A comparison of ultrasound with magnetic resonance imaging in the assessment of fetal biometry and weight in the second trimester of pregnancy: An observer agreement and variability study

Objective

To compare the intra and interobserver variability of ultrasound and magnetic resonance imaging in the assessment of common fetal biometry and estimated fetal weight in the second trimester.

Methods

Retrospective measurements on preselected image planes were performed independently by two pairs of observers for contemporaneous ultrasound and magnetic resonance imaging studies of the same fetus. Four common fetal measurements (biparietal diameter, head circumference, abdominal circumference and femur length) and an estimated fetal weight were analysed for 44 'low risk' cases. Comparisons included, intra-class correlation coefficients, systematic error in the mean differences and the random error.

Results

The ultrasound inter- and intraobserver agreements for ultrasound were good, except intraobserver abdominal circumference (intra-class correlation coefficient = 0.880, poor), significant increases in error was seen with larger abdominal circumference sizes. Magnetic resonance imaging produced good/excellent intraobserver agreement with higher intra-class correlation coefficients than ultrasound. Good interobserver agreement was found for both modalities except for the biparietal diameter (magnetic resonance imaging intra-class correlation coefficient = 0.942, moderate). Systematic errors between modalities were seen for the biparietal diameter, femur length and estimated fetal weight (mean percentage error = +2.5%, -5.4% and -8.7%, respectively, p < 0.05). Random error was above 5% for ultrasound intraobserver abdominal circumference, femur length and estimated fetal weight and magnetic resonance imaging interobserver biparietal diameter, abdominal circumference, femur length and estimated fetal weight (magnetic resonance imaging estimated fetal weight error >10%).

Conclusion

Ultrasound remains the modality of choice when estimating fetal weight, however with increasing application of fetal magnetic resonance imaging a method of assessing fetal weight is desirable. Both methods are subject to random error and operator dependence. Assessment of calliper placement variations may be an objective method detecting larger than expected errors in fetal measurements.

A Deep Learning Solution for Automatic Fetal Neurosonographic Diagnostic Plane Verification Using Clinical Standard Constraints

During routine ultrasound assessment of the fetal brain for biometry estimation and detection of fetal abnormalities, accurate imaging planes must be found by sonologists following a well-defined imaging protocol or clinical standard, which can be difficult for non-experts to do well. This assessment helps provide accurate biometry estimation and the detection of possible brain abnormalities. We describe a machine-learning method to assess automatically that transventricular ultrasound images of the fetal brain have been correctly acquired and meet the required clinical standard. We propose a deep learning solution, which breaks the problem down into three stages: (i) accurate localization of the fetal brain, (ii) detection of regions that contain structures of interest and (iii) learning the acoustic patterns in the regions that enable plane verification. We evaluate the developed methodology on a large real-world clinical data set of 2-D mid-gestation fetal images. We show that the automatic verification method approaches human expert assessment.

Pilot Study of a Software-Supported Protocol for Second-Trimester Ultrasound Screening

OBJECTIVES

To evaluate the feasibility and impact of using a software-supported protocol for routine second-trimester ultrasound scanning.

METHODS

We conducted a comparative observational study of 2 sets of 25 randomly selected normal routine second-trimester examinations performed by the same expert sonographer before and 1 year after the introduction of a software-supported protocol. The scanning protocol was identical during both periods and conformed to International Society of Ultrasound in Obstetrics and Gynecology guidelines. Two independent expert sonographers reviewed the temporal sequences of fetal anatomic visualization. The examination duration, number of images, time per stored image, and number of recorded anatomic features according to the International Society of Ultrasound in Obstetrics and Gynecology guidelines were compared between the periods.

RESULTS

The mean examination duration and the number of images stored ± SD were both significantly higher during the period with the software-supported protocol than during the previous period (18.9 ± 5.3 versus 15.3 ± 2.8 minutes, respectively; P = .005; and 52.0 ± 2.4 versus 35.2 ± 3.4; P < .001). The mean time per image was also shorter with the software-supported protocol (19 ± 7 versus 26 ± 4 seconds; P < .001). Recording of the placental location, amniotic fluid quantification, cavum septi pellucidi, thoracic shape, both kidneys, both arms, and genitalia was significantly more consistent with the software-supported protocol (P < .001; P = .001; P = .022; P = .050; P = .022; P < .001; and P = .048).

CONCLUSIONS

This pilot study suggests that a software-supported protocol standardizing image acquisition may improve operator efficiency during second-trimester ultrasound scans.

[Report from the CFEF seminar on fetal biometry (June 2017)]

This article reports the conclusions and recommendations resulting from the seminar organized in Paris on June 15, 2017 by the scientific committee of the French College of Fetal Ultrasound (CFEF). The purpose of this meeting was to audit the practices in screening for SGA and IUGR fetuses in France and to discuss ways to improve ultrasound screening. A review of charts, references, standards and common practices was performed. The potential new biometric tools applicable in France were reviewed and analyzed. Eventually, options and recommendations for improvement are proposed.

Automatic image quality assessment and measurement of fetal head in two-dimensional ultrasound image

Owing to the inconsistent image quality existing in routine obstetric ultrasound (US) scans that leads to a large intraobserver and interobserver variability, the aim of this study is to develop a quality-assured, fully automated US fetal head measurement system. A texton-based fetal head segmentation is used as a prerequisite step to obtain the head region. Textons are calculated using a filter bank designed specific for US fetal head structure. Both shape- and anatomic-based features calculated from the segmented head region are then fed into a random forest classifier to determine the quality of the image (e.g., whether the image is acquired from a correct imaging plane), from which fetal head measurements [biparietal diameter (BPD), occipital-frontal diameter (OFD), and head circumference (HC)] are derived. The experimental results show a good performance of our method for US quality assessment and fetal head measurements. The overall precision for automatic image quality assessment is 95.24% with 87.5% sensitivity and 100% specificity, while segmentation performance shows 99.27% ([Formula: see text]) of accuracy, 97.07% ([Formula: see text]) of sensitivity, 2.23 mm ([Formula: see text]) of the maximum symmetric contour distance, and 0.84 mm ([Formula: see text]) of the average symmetric contour distance. The statistical analysis results using paired [Formula: see text]-test and Bland-Altman plots analysis indicate that the 95% limits of agreement for inter observer variability between the automated measurements and the senior expert measurements are 2.7 mm of BPD, 5.8 mm of OFD, and 10.4 mm of HC, whereas the mean differences are [Formula: see text], [Formula: see text], and [Formula: see text], respectively. These narrow 95% limits of agreements indicate a good level of consistency between the automated and the senior expert's measurements.

International estimated fetal weight standards of the INTERGROWTH-21st Project

OBJECTIVE

Estimated fetal weight (EFW) and fetal biometry are complementary measures used to screen for fetal growth disturbances. Our aim was to provide international EFW standards to complement the INTERGROWTH-21st Fetal Growth Standards that are available for use worldwide.

METHODS

Women with an accurate gestational-age assessment, who were enrolled in the prospective, international, multicenter, population-based Fetal Growth Longitudinal Study (FGLS) and INTERBIO-21st Fetal Study (FS), two components of the INTERGROWTH-21st Project, had ultrasound scans every 5 weeks from 9-14 weeks' until 40 weeks' gestation. At each visit, measurements of fetal head circumference (HC), biparietal diameter, occipitofrontal diameter, abdominal circumference (AC) and femur length (FL) were obtained blindly by dedicated research sonographers using standardized methods and identical ultrasound machines. Birth weight was measured within 12 h of delivery by dedicated research anthropometrists using standardized methods and identical electronic scales. Live babies without any congenital abnormality, who were born within 14 days of the last ultrasound scan, were selected for inclusion. As most births occurred at around 40 weeks' gestation, we constructed a bootstrap model selection and estimation procedure based on resampling of the complete dataset under an approximately uniform distribution of birth weight, thus enriching the sample size at extremes of fetal sizes, to achieve consistent estimates across the full range of fetal weight. We constructed reference centiles using second-degree fractional polynomial models.

RESULTS

Of the overall population, 2404 babies were born within 14 days of the last ultrasound scan. Mean time between the last scan and birth was 7.7 (range, 0-14) days and was uniformly distributed. Birth weight was best estimated as a function of AC and HC (without FL) as log(EFW) = 5.084820 - 54.06633 × (AC/100)3  - 95.80076 × (AC/100)3  × log(AC/100) + 3.136370 × (HC/100), where EFW is in g and AC and HC are in cm. All other measures, gestational age, symphysis-fundus height, amniotic fluid indices and interactions between biometric measures and gestational age, were not retained in the selection process because they did not improve the prediction of EFW. Applying the formula to FGLS biometric data (n = 4231) enabled gestational age-specific EFW tables to be constructed. At term, the EFW centiles matched those of the INTERGROWTH-21st Newborn Size Standards but, at < 37 weeks' gestation, the EFW centiles were, as expected, higher than those of babies born preterm. Comparing EFW cross-sectional values with the INTERGROWTH-21st Preterm Postnatal Growth Standards confirmed that preterm postnatal growth is a different biological process from intrauterine growth.

CONCLUSIONS

We provide an assessment of EFW, as an adjunct to routine ultrasound biometry, from 22 to 40 weeks' gestation. However, we strongly encourage clinicians to evaluate fetal growth using separate biometric measures such as HC and AC, as well as EFW, to avoid the minimalist approach of focusing on a single value. © 2016 Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Ultrasound-based gestational-age estimation in late pregnancy

OBJECTIVE

Accurate gestational-age (GA) estimation, preferably by ultrasound measurement of fetal crown-rump length before 14 weeks' gestation, is an important component of high-quality antenatal care. The objective of this study was to determine how GA can best be estimated by fetal ultrasound for women who present for the first time late in pregnancy with uncertain or unknown menstrual dates.

METHODS

INTERGROWTH-21^st was a large, prospective, multicenter, population-based project performed in eight geographically defined urban populations. One of its principal components, the Fetal Growth Longitudinal Study, aimed to develop international fetal growth standards. Each participant had their certain menstrual dates confirmed by first-trimester ultrasound examination. Fetal head circumference (HC), biparietal diameter (BPD), occipitofrontal diameter (OFD), abdominal circumference (AC) and femur length (FL) were measured every 5 weeks from 14 weeks' gestation until delivery. For each participant, a single, randomly selected ultrasound examination was used to explore all candidate biometric variables and permutations to build models to predict GA. Regression equations were ranked based upon minimization of the mean prediction error, goodness of fit and model complexity. An automated machine learning algorithm, the Genetic Algorithm, was adapted to evaluate > 64 000 potential polynomial equations as predictors.

RESULTS

Of the 4607 eligible women, 4321 (94%) had a pregnancy without major complications and delivered a live singleton without congenital malformations. After other exclusions (missing measurements in GA window and outliers), the final sample comprised 4229 women. Two skeletal measures, HC and FL, produced the best GA prediction, given by the equation log_e (GA) = 0.03243 × (log_e (HC))² + 0.001644 × FL × log_e (HC) + 3.813. When FL was not available, the best equation based on HC alone was log_e (GA) = 0.05970 × (log_e (HC))² + 0.000000006409 × (HC)³ + 3.3258. The estimated uncertainty of GA prediction (half width 95% interval) was 6-7 days at 14 weeks' gestation, 12-14 days at 26 weeks' gestation and > 14 days in the third trimester. The addition of FL to the HC model led to improved prediction intervals compared with using HC alone, but no further improvement in prediction was afforded by adding AC, BPD or OFD. Equations that included other measurements (BPD, OFD and AC) did not perform better.

CONCLUSIONS

Among women initiating antenatal care late in pregnancy, a single set of ultrasound measurements combining HC and FL in the second trimester can be used to estimate GA with reasonable accuracy. We recommend this tool for underserved populations but considerable efforts should be implemented to improve early initiation of antenatal care worldwide. © 2016 Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Ultrasound Quality Assurance for Singletons in the National Institute of Child Health and Human Development Fetal Growth Studies

OBJECTIVES

To report on the ultrasound quality assurance program for the National Institute of Child Health and Human Development Fetal Growth Studies and describe both its advantages and generalizability.

METHODS

After training on an ultrasound system and software, research sonographers were expected to capture blank (unmeasured) images in triplicate for crown-rump length, biparietal diameter, head circumference, abdominal circumference, and femur length. A primary expert sonographer was designated and validated. A 5% sample (n = 740 of 14,785 scans) was randomly selected in 3 distinct rounds from within strata of maternal body mass index (round 1 only), gestational age, and research site. Unmeasured images were extracted from selected scans and measured with the ultrasound software by an expert sonographer. Correlations and coefficients of variation (CVs) were calculated, and the within-measurement standard deviation (ie, technical error of the measurement), was calculated.

RESULTS

The reliability between the site sonographers and the expert was high, with correlations exceeding 0.99 for all dimensions in all rounds. The CV % values showed low variability, with the percentage differences being less than 2%, except for abdominal circumference in rounds 2 and 3, in which it averaged about 3%. Correlations remained high (>0.90) with increasing fetal size; there was a monotonic increase in technical errors of the measurement but without a corresponding increase in the CV %.

CONCLUSIONS

Using rigorous procedures for training sonographers, coupled with quality assurance oversight, we determined that the measurements acquired longitudinally for singletons are both accurate and reliable for establishment of an ultrasound standard for fetal growth.

[Is the stomach a main landmark on the abdominal circumference? Audit of 3 operators]

OBJECTIVES

The fetal weight estimation depends largely on the accuracy of abdominal circumference. The quality criteria are standardized to minimize variability and include visualization of the stomach. The objective of this study is to investigate the presence or absence of the stomach on the abdominal circumference for 3 different operators.

MATERIAL AND METHODS

We conducted re-reading of 204 ultrasound images in the second and third trimester of pregnancy, performed by three operators, at the maternity Port Royal in Paris in 2013. On these images, the presence of the stomach was sought and other quality criteria were verified.

RESULTS

Among the 204 images, 166 included the stomach (81%). When studying for each of the three operators, there were 79%, 72% and 98% of the stomach into the abdominal circumference, a significant difference between operators (P=0.0029). Regarding the secondary criteria, the quality criteria found most often were the calipers and well placed ellipse (89%).

CONCLUSION

According to the previous studies, the stomach seems to be a reference to search. Our study shows variability depending on the different operators. If a hierarchy of quality criteria is to be considered, the stomach does not seem to be the first criterion to search.

Measurement of abdominal circumference in preterm infants

BACKGROUND

Body weight, length and head and thoracic circumference are routinely measured in obstetric and neonatal departments. Reference values for these measurements have been established for the neonatal population. Neonatal abdominal circumference is not routinely measured, and no reference values for this measurement have been determined. To evaluate the increase in abdominal circumference in newborns with abdominal pathology such as necrotizing enterocolitis, information about normal abdominal circumference in healthy neonates shortly after birth is needed. The aim of this study was to determine the correlation between abdominal circumference and birth weight by measuring the abdominal circumference of premature neonates soon after birth.

METHODS

Abdominal circumference was measured within 30 min of birth in 220 neonates born between 23 and 35 weeks' gestation.

RESULTS

There was no statistically significant difference in abdominal circumference between boys and girls in the study population. A specific formula for estimating normal abdominal circumference was developed: y = 0.0053x + 14.83 (y = abdominal circumference in cm; x = body weight in g; 0.0053 = regression coefficient; 14.83 = regression constant).

CONCLUSION

A positive linear correlation between abdominal circumference and birth weight was found in infants at birth. The correlation can be summarized as a linear regression equation. Further studies are needed to investigate possible factors associated with abdominal circumference in fed versus unfed preterm infants.