Loïc Lalys

Estimation of gestational age from tooth germs: Biometric study of DentaScan images.

Abstract:  The few available studies on fetal age estimation concern very small samples, and statistical analysis is sometimes inadequate. In this survey, we used germs of deciduous teeth to estimate fetal age. Forty‐nine fetuses and 40 mandibles were scanned, and observations and measurements were made on DentaScan images. After checking their repeatability and reproducibility (analysis of variance), we defined thresholds using Fisher’s linear discriminant analysis to calculate the probability that a fetus was over or below a predefined age threshold. The forensic threshold which is of particular interest in France is 22 weeks amenorrhea. Relationships between fetal age and deciduous germ measurements were then sought by multiple linear regression. The thresholds gave very good results: 91.84% of good probability for the threshold of 22 weeks amenorrhea with no chance of error. The most precise age evaluation obtained nevertheless gave a range of ±4.6 weeks amenorrhea, so greater accuracy is still needed.

Ultrasound measurement of total body fat in obese adolescents

Background/Aims: To compare body fat (BF) measurements obtained with a new ultrasound method with those assessed by dual-energy X-ray absorptiometry (DEXA) in obese adolescents. Methods: In 94 adolescents (57 females and 37 males) aged 12–19 years and body mass index (BMI) exceeding 30 kg·m–2, the z-score BMI for age was 6.7 (adolescent girls) and 6.6 (adolescent boys) >97th percentile. BF was measured using DEXA and a method based on ultrasound measurements, body weight, height, abdominal circumference and mid-thigh circumference. Results: Obesity class I was noted in 39%, II in 28% and III in 33% of the patients. BF by ultrasound correlated closely with BF by DEXA, in both females (r = 0.958) and males (r = 0.981), with standard errors of the estimates (SEE) being 2.9 and 2.5 kg, respectively. The ultrasound method was more accurate than the skinfold technique (n = 24; SEE: 2.2 vs. 6.5 kg, respectively). In 13 adolescents who had marked weight loss after 6 months of treatment, the decrease in DEXA-measured BF correlated closely with the decrease in ultrasound-measured BF (r = 0.95). Conclusions: Our innovative portable ultrasound technique has advantages in terms of reliability, reproducibility, accuracy and costs for screening and monitoring obese adolescents. A patent application has been submitted. Our method should prove valuable for epidemiological studies.

Child pedestrian anthropometry: evaluation of potential impact points during a crash

This paper highlights the potential impact points of a child pedestrian during a crash with the front end of a vehicle. Child anthropometry was defined for ages between 3 and 15 years. It was based on the measurement of seven different segment body heights (knee, femur, pelvis, shoulder, neck, chin, vertex) performed on about 2,000 French children. For each dimension, the 5(th), 50(th) and 95(th) percentile values were reported, and the corresponding linear regression lines were given. Then these heights were confronted with three different vehicle shapes, corresponding to a passenger car, a sport utility vehicle and a light truck, to identify impact points. In particular, we show that the thigh is directly hit by the bumper for children above 12 years of age, whereas the head principally impacts the hood. The influence of child anthropometry on the pedestrian trajectory and the comparison with test procedures in regulation are discussed.

Small and large foetuses: Identification and estimation of foetal weight at delivery from third-trimester ultrasound data

BACKGROUND The estimation of foetal weight (EFW) at delivery is crucial to assess the risk of foetal and neonatal morbidity and mortality, most notably when the foetus is small or large. AIM To accurately predict the EFW at delivery of small foetuses (birth weight [BW]≤2500g) and large foetuses (BW≥4000g) identified with third-trimester ultrasound data. METHODS We included 1309 foetuses whose age and weight at birth were known and for whom standard data were available from third-trimester ultrasound scans. Small and large foetuses were identified by extrapolation to full term of the estimated foetal weight obtained using Hadlocks equation. We built two regression models for predicting the birth weights of small and large foetuses, respectively. The results obtained with these models were compared to those obtained with Hadlocks equation. RESULTS Third-trimester sonograms were obtained at 33.6±1.3 weeks gestational age [WGA] and birth occurred at 38.7±1.2WGA. EFW of small foetuses predicted using the regression model showed significantly less systematic bias than the Hadlock estimate (2.3% vs. 7.2%, respectively), whereas random errors were similar. EFW of large foetuses predicted using the regression model showed significantly less random error than the Hadlock estimate (6.2% vs. 10.1%, respectively), whereas systematic bias was similar. Data from an independent validation sample indicate that our regression models are accurate. CONCLUSIONS To apply distinct models for accurately predicting the EFWs at delivery of small and large foetuses should prevent adverse events related to newborn size.

Age at menarche in a group of French schoolgirls

Mean age at menarche in France decreased from 12.78 years in 1979 to 12.6 years in 1994. The aim of this study was to determine mean age at first menstruation in French adolescent girls in order to study the secular trend.

Body Fat Mass Assessment: A Comparison between an Ultrasound-Based Device and a Discovery A Model of DXA.

Objective. To examine measurement of body composition by ultrasound compared with a reference technique:dual energy X-ray absorptiometry (DXA). We evaluated the accuracy of a portable ultrasound-based device in estimating total body fat mass with those assessed by DXA in adult. Methods. Body fat mass has been estimated using a portable ultrasound-based device in comparison with a contemporary reference DXA apparatus: the Hologic Discovery A. Anthropometric data has been assessed in order to maximize the output of the software associated with the ultrasound-based device. A cross-validation between ultrasound technique (US) and DXA was developed in this study. Total body fat mass estimated by ultrasound was compared with this DXA model in a sample of 83 women and 41 men. Results. Ultrasound technique (US) of body fat (BF) was better correlated with DXA in both women (r 2 = 0.97, P < 0.01) and men (r 2 = 0.92, P < 0.01) with standard errors of estimates (SEE) being 2.1 kg and 2.2 kg, respectively. Conclusion. The use of a portable device based on a US produced a very accurate BF estimate in relation to DXA reference technique. As DXA absorptiometry techniques are not interchangeable, the use of our ultrasound-based device needs to be recalibrated on a more contemporary DXA.