Israel Medical Association Journal

Background: Sonographic estimation of birth weight may differ among evaluators due to its operator-dependent nature.

Objectives: To compare the accuracy of estimation of fetal birth weight by sonography between ultrasound-certified physicians and registered diagnostic medical technicians.

Methods: The authors reviewed ultrasound examinations that had been performed by either technicians or ultrasound-certified obstetricians between 2010 and 2017, and within 2 days of delivery. Inclusion criteria were: singleton viable pregnancy, details of four ultrasound measurements (abdominal circumference, bi-parietal diameter, head circumference, and femur length), and known birth weight. The estimated fetal weight (EFW) was calculated according to the Hadlock formula, incorporating the four ultrasound measurements. The mean percentage error (MPE) was calculated by the formula: (EFW-birth weight) x100 / birth weight.

Results: Technicians performed 9741examinations and physicians performed 352 examinations. The proportion of macrosomic neonates was similar in both groups. Technicians were more accurate than physicians in terms of the MPE, absolute MPE, proportion of estimates that fell within ± 10% of birth weight, and Euclidean distance (P < 0.0001 for all comparisons). They were also more accurate in terms of sensitivity, specificity, positive predictive value, negative predictive value, and area under the receiver operating curve. Furthermore, for fetuses weighing more than 4000 grams the technicians had a lower total false prediction rate.

Conclusions: Medical technicians in our institute performed better than physicians in estimating fetal weight. Further studies are warranted to confirm our findings and better delineate the role of repeat physician’s examination after an initial estimation by an experienced technician.

Background: Selection of appropriate reference charts for fetal biometry is mandatory to ensure an accurate diagnosis. Most hospitals and clinics in Israel use growth curves from the United States. Charts developed in different populations do not perform well in the Israeli population.

Objectives: To construct new reference charts for fetal biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL), using a large sample of fetuses examined at 14–42 weeks gestational age in a medical center and a community ultrasound unit located in two different regions of Israel. 

Methods: Data from the medical center and the community clinic were pooled. The mean and standard error of each measure for each week was calculated. Based on these, reference charts were calculated using quantiles of the normal distribution. The performance of the reference charts was assessed by comparing the new values to empirical quantiles.

Results: Biometric measurements were obtained for 79,328 fetuses. Growth charts were established based on these measurements. The overall performance of the curves was very good, with only a few exceptions among the higher quantiles in the third trimester in the medical center subsample.

Conclusions: We present new local reference charts for fetal biometry, derived from a large and minimally selected Israeli population. We suggest using these new charts in routine daily obstetric practice.