Principles and clinical methods of body surface gastric mapping: Technical review.

BACKGROUND AND PURPOSE: Chronic gastric symptoms are common, however differentiating specific contributing mechanisms in individual patients remains challenging. Abnormal gastric motility is present in a significant subgroup, but reliable methods for assessing gastric motor function in clinical practice are lacking. Body surface gastric mapping (BSGM) is a new diagnostic aid, employs multi-electrode arrays to measure and map gastric myoelectrical activity non-invasively in high resolution. Clinical adoption of BSGM is currently expanding following studies demonstrating the ability to achieve specific patient subgrouping, and subsequent regulatory clearances. An international working group was formed in order to standardize clinical BSGM methods, encompassing a technical group developing BSGM methods and a clinical advisory group. The working group performed a technical literature review and synthesis focusing on the rationale, principles, methods, and clinical applications of BSGM, with secondary review by the clinical group. The principles and validation of BSGM were evaluated, including key advances achieved over legacy electrogastrography (EGG). Methods for BSGM were reviewed, including device design considerations, patient preparation, test conduct, and data processing steps. Recent advances in BSGM test metrics and reference intervals are discussed, including four novel metrics, being the 'principal gastric frequency', BMI-adjusted amplitude, Gastric Alimetry Rhythm Index™, and fed: fasted amplitude ratio. An additional essential element of BSGM has been the introduction of validated digital tools for standardized symptom profiling, performed simultaneously during testing. Specific phenotypes identifiable by BSGM and the associated symptom profiles were codified with reference to pathophysiology. Finally, knowledge gaps and priority areas for future BSGM research were also identified by the working group.

Do patient characteristics matter when calculating sample size for eczema clinical trials?

Background: The Patient-Oriented Eczema Measure (POEM) is the core outcome instrument recommended for measuring patient-reported atopic eczema symptoms in clinical trials. To ensure that the statistical significance of clinical trial results is meaningful, trials are often designed by specifying the target difference in the primary outcome as part of the sample size calculation. One method used to specify the target difference is a score that corresponds to a standardized effect size. Objectives: to assess how the standardized effect size of POEM scores vary across age, gender, ethnicity and disease severity. Methods: This study combined data from five UK-based randomized clinical trials of eczema treatments in order to assess differences in self-reported eczema symptoms (POEM) corresponding to a standardized effect size (0.5 SD of baseline POEM scores) across age, gender, ethnicity and disease severity. Results: POEM scores corresponding to 0.5 SD(baseline) were remarkably consistent across participants of varying ages, gender, ethnicity and disease severity from datasets of five UK trials in children (range 2.99-3.45). Conclusions: This study provides information that can support those designing clinical trials to determine their sample size and can aid individuals interpreting trial results. Further exploration of differences in populations beyond the United Kingdom is needed.

A national Health and Work Strategy: a search for evidence.

BACKGROUND: The Health and Safety Executive's new Health and Work Strategy is based on an up-to-date assessment of workplace health priorities. Rather than replicating traditional prioritization approaches, a broader assessment of health and work priorities was carried out using a range of stakeholders. AIMS: To develop a set of health priorities for further research and intervention activity. METHODS: Four exercises were carried out, including internal prioritization, two external web-hosted questionnaire studies of younger workers and occupational health professionals, focus groups and tele-depth interviews with workplace health and safety professionals. RESULTS: The highest rated internal priorities (weighted priority scores) were identified as mesothelioma (70), lung cancer (69.25), chronic obstructive pulmonary disease (COPD; 69), musculoskeletal disorders (MSDs; 66.25), hearing loss (65.75), stress (65.5), asthma (64.5) and hand-arm vibration syndrome (61.5). Using the three highest ranked criteria developed by occupational health professionals ((i) the preventability of the condition, (ii) the impact of the condition and (iii) the number of workers affected), mesothelioma, lung cancer, COPD, MSDs, hearing loss, stress and asthma were identified as the top seven priorities. Generic issues identified included ageing and work, obesity, newer technologies, and ethnicity and cultures of workforces. Apprentices identified stress, depression, anxiety, musculoskeletal and respiratory disorders, fatigue and workload as important workplace health considerations. CONCLUSIONS: This process identified a number of expected and new areas of health research interest. We believe the findings reflect the real world requirements of work as assessed by occupational health and safety practitioners and workers.

Underestimation of spirometry if recommended testing guidance is not followed.

Background: Lung function measured at work is used to make important employment decisions. Improving its quality will reduce misclassification and allow more accurate longitudinal interpretation over time. Aims: To assess the amount by which lung function (forced expiratory volume in 1 second [FEV1] and forced vital capacity [FVC]) values will be underestimated if recommended spirometry testing guidance is not followed. Methods: Lung function was measured in a population of workers. Knowledge of the final reproducible FEV1 and FVC for each worker allowed estimation of the underestimates that would have occurred if less forced manoeuvres than recommended had been performed. Results: A total of 667 workers (661 males, mean age 43 years, range 18-66) participated. Among them, 560 (84%) achieved reproducible results for both FEV1 and FVC; 470 (84%) of these did so after three technically acceptable forced expiratory manoeuvres, a cumulative total of 533 after four, 548 after five, 557 after six, 559 after seven and 560 after eight blows. If only one (or first two) technically acceptable blow(s) had been performed, mean underestimates were calculated for FEV1 of 115.1 ml (35.4 ml) and for FVC of 143.4 ml (42.3 ml). Conclusions: In this study, reproducible spirometry was achievable in most workers. Not adhering to standards underestimates lung function by clinically significant amounts.

How should minimally important change scores for the Patient-Oriented Eczema Measure be interpreted? A validation using varied methods.

BACKGROUND: The Patient-Oriented Eczema Measure (POEM), scored 0-28, is the core outcome instrument recommended for measuring patient-reported atopic eczema symptoms in clinical trials. To date, two published studies have broadly concurred that the minimally important change (MIC) of the POEM is three points. Further assessment of the MIC of POEM in different populations, and using a variety of methods, will improve interpretability of the POEM in research and clinical practice. OBJECTIVES: To calculate the smallest detectable change in the POEM and estimate the MIC of the POEM using a variety of methods in a trial dataset of children with moderate-to-severe atopic eczema. METHODS: This study used distribution-based and anchor-based methods to calculate the MIC of the POEM in children with moderate-to-severe eczema. RESULTS: Data were collected from 300 children. The smallest detectable change was 2·13. The MIC estimates were 1·07 (using 0·2 SD of baseline POEM scores) and 2·68 (using 0·5 SD of baseline POEM scores) based on distribution-based methods; were 3·09-6·13 based on patient-/parent-reported anchor-based methods; and were 3·23-5·38 based on investigator-reported anchor-based methods. CONCLUSIONS: We recommend the following thresholds be used to interpret changes in POEM scores: ≤ 2, unlikely to be a change beyond measurement error; 2·1-2·9, a small change detected that is likely to be beyond measurement error but may not be clinically important; 3-3·9, probably a clinically important change; ≥ 4, very likely to be a clinically important change.

Labour induction near term for women aged 35 or over: an economic evaluation.

OBJECTIVE: Induction of labour at 39 weeks for nulliparous women aged 35 years and over may prevent stillbirths and does not increase caesarean births, so it may be popular. But the overall costs and benefits of such a policy have not been compared. DESIGN: A cost-utility analysis alongside a randomised controlled trial (the 35/39 trial). SETTING: Obstetric departments of 38 UK National Health Service hospitals and one UK primary-care trust. POPULATION: Nulliparous women aged 35 years or over on their expected due date, with a singleton live fetus in a cephalic presentation. METHODS: Costs were estimated from the National Health Service and Personal Social Services perspective and quality-adjusted life-years (QALYs) were calculated based on patient responses to the EQ-5D at baseline and 4 weeks. MAIN OUTCOME MEASURES: Data on antenatal care, mode of delivery, analgesia in labour, method of induction, EQ-5D (baseline and 4 weeks postnatal) and participant-administered postnatal health resource use data were collected. RESULTS: The intervention was associated with a mean cost saving of £263 and a small additional gain in QALYs (though this was not statistically significant), even without considering any possible QALY gains from stillbirth prevention. CONCLUSION: A policy of induction of labour at 39 weeks for women of advanced maternal age would save money. TWEETABLE ABSTRACT: A policy of induction of labour at 39 weeks of gestation for women of advanced maternal age would save money.

Patient-Reported Outcomes after Monitoring, Surgery, or Radiotherapy for Prostate Cancer.

BACKGROUND: Robust data on patient-reported outcome measures comparing treatments for clinically localized prostate cancer are lacking. We investigated the effects of active monitoring, radical prostatectomy, and radical radiotherapy with hormones on patient-reported outcomes. METHODS: We compared patient-reported outcomes among 1643 men in the Prostate Testing for Cancer and Treatment (ProtecT) trial who completed questionnaires before diagnosis, at 6 and 12 months after randomization, and annually thereafter. Patients completed validated measures that assessed urinary, bowel, and sexual function and specific effects on quality of life, anxiety and depression, and general health. Cancer-related quality of life was assessed at 5 years. Complete 6-year data were analyzed according to the intention-to-treat principle. RESULTS: The rate of questionnaire completion during follow-up was higher than 85% for most measures. Of the three treatments, prostatectomy had the greatest negative effect on sexual function and urinary continence, and although there was some recovery, these outcomes remained worse in the prostatectomy group than in the other groups throughout the trial. The negative effect of radiotherapy on sexual function was greatest at 6 months, but sexual function then recovered somewhat and was stable thereafter; radiotherapy had little effect on urinary continence. Sexual and urinary function declined gradually in the active-monitoring group. Bowel function was worse in the radiotherapy group at 6 months than in the other groups but then recovered somewhat, except for the increasing frequency of bloody stools; bowel function was unchanged in the other groups. Urinary voiding and nocturia were worse in the radiotherapy group at 6 months but then mostly recovered and were similar to the other groups after 12 months. Effects on quality of life mirrored the reported changes in function. No significant differences were observed among the groups in measures of anxiety, depression, or general health-related or cancer-related quality of life. CONCLUSIONS: In this analysis of patient-reported outcomes after treatment for localized prostate cancer, patterns of severity, recovery, and decline in urinary, bowel, and sexual function and associated quality of life differed among the three groups. (Funded by the U.K. National Institute for Health Research Health Technology Assessment Program; ProtecT Current Controlled Trials number, ISRCTN20141297 ; ClinicalTrials.gov number, NCT02044172 .).

Diabetic gastroparesis alters the biomagnetic signature of the gastric slow wave.

BACKGROUND: Gastroparesis is characterized by delayed gastric emptying without mechanical obstruction, but remains difficult to diagnose and distinguish from other gastrointestinal (GI) disorders. Gastroparesis affects the gastric slow wave, but non-invasive assessment has been limited to the electrogastrogram (EGG), which reliably characterizes temporal dynamics but does not provide spatial information. METHODS: We measured gastric slow wave parameters from the EGG and magnetogastrogram (MGG) in patients with gastroparesis and in healthy controls. In addition to dominant frequency (DF) and percentage power distribution (PPD), we measured the propagation velocity from MGG spatiotemporal patterns and the percentage of slow wave coupling (%SWC) from EGG. KEY RESULTS: No significant difference in DF was found between patients and controls. Gastroparesis patients had lower percentages of normogastric frequencies (60 ± 6% vs 78 ± 4%, p < 0.05), and higher brady (9 ± 2% vs 2 ± 1%, p < 0.05) and tachygastric (31 ± 2% vs 19 ± 1%, p < 0.05) frequency content postprandial, indicative of uncoupling. Propagation patterns were substantially different in patients and longitudinal propagation velocity was retrograde at 4.3 ± 2.9 mm/s vs anterograde at 7.4 ± 1.0 mm/s for controls (p < 0.01). No difference was found in %SWC from EGG. CONCLUSIONS & INFERENCES: Gastric slow wave parameters obtained from MGG recordings distinguish gastroparesis patients from controls. Assessment of slow wave propagation may prove critical to characterization of underlying disease processes. Future studies should determine pathologic indicators from MGG associated with other functional gastric disorders, and whether multichannel EGG with appropriate signal processing also reveals pathology.

Characterization of Electrophysiological Propagation by Multichannel Sensors.

OBJECTIVE: The propagation of electrophysiological activity measured by multichannel devices could have significant clinical implications. Gastric slow waves normally propagate along longitudinal paths that are evident in recordings of serosal potentials and transcutaneous magnetic fields. We employed a realistic model of gastric slow wave activity to simulate the transabdominal magnetogastrogram (MGG) recorded in a multichannel biomagnetometer and to determine characteristics of electrophysiological propagation from MGG measurements. METHODS: Using MGG simulations of slow wave sources in a realistic abdomen (both superficial and deep sources) and in a horizontally-layered volume conductor, we compared two analytic methods (second-order blind identification, SOBI and surface current density, SCD) that allow quantitative characterization of slow wave propagation. We also evaluated the performance of the methods with simulated experimental noise. The methods were also validated in an experimental animal model. RESULTS: Mean square errors in position estimates were within 2 cm of the correct position, and average propagation velocities within 2 mm/s of the actual velocities. SOBI propagation analysis outperformed the SCD method for dipoles in the superficial and horizontal layer models with and without additive noise. The SCD method gave better estimates for deep sources, but did not handle additive noise as well as SOBI. CONCLUSION: SOBI-MGG and SCD-MGG were used to quantify slow wave propagation in a realistic abdomen model of gastric electrical activity. SIGNIFICANCE: These methods could be generalized to any propagating electrophysiological activity detected by multichannel sensor arrays.

Occupational chronic obstructive pulmonary disease: a standard of care.

BACKGROUND: Consistent evidence from population studies report that 10-15% of the total burden of chronic obstructive pulmonary disease (COPD) is associated with workplace exposures. This proportion of COPD could be eliminated if harmful workplace exposures were controlled adequately. AIMS: To produce a standard of care for clinicians, occupational health professionals, employers and employees on the identification and management of occupational COPD. METHODS: A systematic literature review was used to identify published data on the prevention, identification and management of occupational COPD. Scottish Intercollegiate Guidance Network grading and the Royal College of General Practitioner three star grading system were used to grade the evidence. RESULTS: There are a number of specific workplace exposures that are established causes of COPD. Taking an occupational history in patients or workers with possible or established COPD will identify these. Reduction in exposure to vapours, gases, dusts and fumes at work is likely to be the most effective method for reducing occupational COPD. Identification of workers with rapidly declining lung function, irrespective of their specific exposure, is important. Individuals can be identified at work by accurate annual measures of lung function. CONCLUSIONS: Early identification of cases with COPD is important so that causality can be considered and action taken to reduce causative exposures thereby preventing further harm to the individual and other workers who may be similarly exposed. This can be achieved using a combination of a respiratory questionnaire, accurate lung function measurements and control of exposures in the workplace.

Noninvasive biomagnetic detection of intestinal slow wave dysrhythmias in chronic mesenteric ischemia.

Chronic mesenteric ischemia (CMI) is a challenging clinical problem that is difficult to diagnose noninvasively. Diagnosis early in the disease process would enable life-saving early surgical intervention. Previous studies established that superconducting quantum interference device (SQUID) magnetometers detect the slow wave changes in the magnetoenterogram (MENG) noninvasively following induction of mesenteric ischemia in animal models. The purpose of this study was to assess functional physiological changes in the intestinal slow wave MENG of patients with chronic mesenteric ischemia. Pre- and postoperative studies were conducted on CMI patients using MENG and intraoperative recordings using invasive serosal electromyograms (EMG). Our preoperative MENG recordings showed that patients with CMI exhibited a significant decrease in intestinal slow wave frequency from 8.9 ± 0.3 cpm preprandial to 7.4 ± 0.1 cpm postprandial (P < 0.01) that was not observed in postoperative recordings (9.3 ± 0.2 cpm preprandial and 9.4 ± 0.4 cpm postprandial, P = 0.86). Intraoperative recording detected multiple frequencies from the ischemic portion of jejunum before revascularization, whereas normal serosal intestinal slow wave frequencies were observed after revascularization. The preoperative MENG data also showed signals with multiple frequencies suggestive of uncoupling and intestinal ischemia similar to intraoperative serosal EMG. Our results showed that multichannel MENG can identify intestinal slow wave dysrhythmias in CMI patients.

The effects of homelessness on Veterans' health care service use: an evaluation of independence from comorbidities.

OBJECTIVES: This study evaluates the prevalence of Multiple Comorbid Chronic Disease (MCCD) within homeless and non-homeless Veterans and the association between MCCD and inpatient medical care. METHODS: All individuals seen in the VA North Texas Health Care System between October 1, 2009 and September 30, 2010 (n = 102,034) were evaluated. Homelessness during the year and the number of common chronic diseases were evaluated for an association with likelihood of medical and psychiatric hospitalizations, bed days of care, inpatient substance treatment, rehabilitation admissions, and emergency department visits. RESULTS: Homeless Veterans had higher all-cause mortality rates and rates of use of almost all resources after controlling for chronic disease burden using the Charlson Comorbidity Index, psychiatric illnesses, substance use disorders, and demographic variables. CONCLUSIONS: Homelessness Veterans are vulnerable to a high use of resources and mortality, independent of medical and psychiatric conditions. This finding should focus additional attention on reducing homelessness.

Effects of body mass index on gastric slow wave: a magnetogastrographic study.

We measured gastric slow wave activity simultaneously with magnetogastrogram (MGG), mucosal electromyogram (EMG) and electrogastrogram (EGG) in human subjects with varying body mass index (BMI) before and after a meal. In order to investigate the effect of BMI on gastric slow wave parameters, each subject's BMI was calculated and divided into two groups: subjects with BMI ≤ 27 and BMI > 27. Signals were processed with Fourier spectral analysis and second-order blind identification (SOBI) techniques. Our results showed that increased BMI does not affect signal characteristics such as frequency and amplitude of EMG and MGG. Comparison of the postprandial EGG power, on the other hand, showed a statistically significant reduction in subjects with BMI > 27 compared with BMI ≤ 27. In addition to the frequency and amplitude, the use of SOBI-computed propagation maps from MGG data allowed us to visualize the propagating slow wave and compute the propagation velocity in both BMI groups. No significant change in velocity with increasing BMI or meal was observed in our study. In conclusion, multichannel MGG provides an assessment of frequency, amplitude and propagation velocity of the slow wave in subjects with differing BMI categories and was observed to be independent of BMI.

Smoking cessation in the workplace.

BACKGROUND: The workplace is an important setting for reaching potentially large numbers of smokers. AIMS: To review the evidence about smoking cessation in the workplace. METHODS: Literature review including a synthesis of findings from recent systematic reviews and meta-analyses of workplace smoking cessation programmes, a separate review of the qualitative evidence, case studies and an expert panel assessment. RESULTS: We found advantages, identified or confirmed from the mixed methods used in this work to holding smoking cessation programmes in the workplace. These included: (i) easy access to large numbers of worker populations for large workplaces, (ii) the potential improved recruitment to such programmes given this, (iii) the opportunity to access young men, traditionally difficult to achieve, (iv) access to occupational health and other staff who can assist with support and delivery and (v) ability for workers to attend relatively easily. Evidence on the importance of developing peer support at work was mixed. The simple provision or availability of programmes and interventions was unlikely to provide any beneficial behaviour change. Interventions should target workers that actively want to stop smoking, use elements that workers have identified as useful or focus on altering beliefs about smoking and the need to stop. CONCLUSIONS: Smoking cessation programmes at work can provide useful support for workers wishing to stop smoking. They are only likely to be effective if participants have moved beyond the contemplation stage regarding smoking cessation, so that stopping smoking is a personal priority.

Noninvasive biomagnetic detection of isolated ischemic bowel segments.

The slow wave activity was measured in the magnetoenterogram (MENG) of normal porcine subjects (N = 5) with segmental intestinal ischemia. The correlation changes in enteric slow wave activity were determined in MENG and serosal electromyograms (EMG). MENG recordings show significant changes in the frequency and power distribution of enteric slow-wave signals during segmental ischemia, and these changes agree with changes observed in the serosal EMG. There was a high degree of correlation between the frequency of the electrical activity recorded in MENG and in serosal EMG (r = 0.97). The percentage of power distributed in brady- and normoenteric frequency ranges exhibited significant segmental ischemic changes. Our results suggest that noninvasive MENG detects ischemic changes in isolated small bowel segments.

Effect of Body Mass Index on the sensitivity of Magnetogastrogram and Electrogastrogram.

AIM: Gastric disorders affect the gastric slow wave. The cutaneous electrogastrogram (EGG) evaluates the electrical potential of the slow wave but is limited by the volume conduction properties of the abdominal wall. The magnetogastrogram (MGG) evaluates the gastric magnetic field activity and is not affected as much by the volume conductor properties of the abdominal wall. We hypothesized that MGG would not be as sensitive to body mass index as EGG. METHODS: We simultaneously recorded gastric slow wave signals with mucosal electrodes, a Superconducting Quantum Interference Device magnetometer (SQUID) and cutaneous electrodes before and after a test meal. Data were recorded from representative pools of human volunteers. The sensitivity of EGG and MGG was compared to the body mass index and waist circumference of volunteers. RESULTS: The study population had good linear regression of their Waist circumference (Wc) and Body Mass Index (BMI) (regression coefficient, R=0.9). The mean BMI of the study population was 29.2 ±1.8 kgm-2 and mean Wc 35.7±1.4 inch. We found that while subjects with BMI≥25 showed significant reduction in post-prandial EGG sensitivity, only subjects with BMI≥30 showed similar reduction in post-prandial MGG sensitivity. Sensitivity of SOBI "EGG and MGG" was not affected by the anthropometric measurements. CONCLUSIONS: Compared to electrogastrogram, the sensitivity of the magnetogastrogram is less affected by changes in body mass index and waist circumference. The use of Second Order Blind Identification (SOBI) increased the sensitivity of EGG and MGG recordings and was not affected by BMI or waist circumference.

Biomagnetic and bioelectric detection of gastric slow wave activity in normal human subjects--a correlation study.

We measured gastric slow wave activity simultaneously with a Superconducting Quantum Interference Device (SQUID) magnetometer, mucosal electrodes and cutaneous electrodes in 18 normal human subjects (11 women and 7 men). We processed signals with Fourier spectral analysis and SOBI blind-source separation techniques. We observed a high waveform correlation between the mucosal electromyogram (EMG) and multichannel SQUID magnetogastrogram (MGG). There was a lower waveform correlation between the mucosal EMG and cutaneous electrogastrogram (EGG), but the correlation improved with the application of SOBI. There was also a high correlation between the frequency of the electrical activity recorded in the MGG and in mucosal electrodes (r = 0.97). We concluded that SQUID magnetometers noninvasively record gastric slow wave activity that is highly correlated with the activity recorded by invasive mucosal electrodes.

Influence of body parameters on gastric bioelectric and biomagnetic fields in a realistic volume conductor.

Electrogastrograms (EGG) and magnetogastrograms (MGG) provide two complementary methods for non-invasively recording electric or magnetic fields resulting from gastric electrical slow wave activity. It is known that EGG signals are relatively weak and difficult to reliably record while magnetic fields are, in theory, less attenuated by the low-conductivity fat layers present in the body. In this paper, we quantified the effects of fat thickness and conductivity values on resultant magnetic and electric fields using anatomically realistic torso models and trains of dipole sources reflecting recent experimental results. The results showed that when the fat conductivity was increased, there was minimal change in both potential and magnetic fields. However, when the fat conductivity was reduced, the magnetic fields were largely unchanged, but electric potentials had a significant change in patterns and amplitudes. When the thickness of the fat layer was increased by 30 mm, the amplitude of the magnetic fields decreased 10% more than potentials but magnetic field patterns were changed about four times less than potentials. The ability to localize the underlying sources from the magnetic fields using a surface current density measure was altered by less than 2 mm when the fat layer was increased by 30 mm. In summary, results confirm that MGG provides a favorable method over EGG when there are uncertain levels of fat thickness or conductivity.

Clinical implications of machine-probe combinations on obstetric ultrasound measurements used in pregnancy dating.

OBJECTIVE: To investigate the effect of use of different machine-probe combinations on measurement variability and to assess how this variability impacts on accuracy of pregnancy dating. METHODS: Sixteen different ultrasound machine-probe combinations were used for lateral measurement of targets spaced 10 and 40 mm apart and axial measurement of targets spaced 10 and 50 mm apart in an ultrasound phantom, and differences between the measured and true values were determined. The mean of the 40-mm lateral measurements was used to estimate gestational age using standard obstetric dating tables for crown-rump length (CRL) and femur length (FL) and the mean of the 50-mm axial measurements was used to estimate gestational age using the obstetric dating tables for biparietal diameter (BPD). RESULTS: As absolute measurements became larger, differences observed using different machine-probe combinations exceeded those due to intraobserver variability. Maximum dating differences for first-trimester CRL of 2 days (based on a measured CRL range of 39-42 mm), second-trimester BPD of 4 days (based on a measured BPD range of 49-52 mm) and FL of 9 days (based on a measured FL range of 39-42 mm) were observed when measurements were transposed to the equivalent gestational age using standard charts. CONCLUSION: Differences between measured and true values of biometric measurements reflect both machine-probe and intraobserver variability. Incremental first-trimester CRL growth with time is rapid, but second-trimester FL growth is much less so, leaving this lateral measurement more prone to both observer and machine-probe errors. The only axial growth measurement commonly performed is BPD where the measurement differences were intermediate between those of CRL and FL. The differences that can be ascribed to different equipment combinations are in many cases greater than those expected in clinical practice and are of potential importance in determining how fetal biometry is used for dating pregnancies.