Comparison of sonographic weight estimation to actual birth weight - A retrospective analysis.

Aim: This retrospective study aims at determining the accuracy of sonograph ic estimation of birth weight based on ultrasound examinations performed at the department of gynaecology of Philipps University at Marburg, Germany. Method: 630 children were born at the university department of gynaecology during the first six months of 1998. 519 babies had been examined sonograph ically and their birth weight estimated within ten days prior to delivery. 176 (33,91 %) of these examinations were carried out by experienced sonogra phers complying to the level II standard of performance set out by DEGUM. 3 43 (66.09%) of examinations were performed by less experienced junior docto rs at the time of the mothers' admission to the delivery room. Two referenc e tables published by Hansmann and Ferrero were used to estimate birth weig ht. Results: The lower and upper quartile of deviation between estimated we ight and actual weight came to -200 g and +200 g using the Hansmann method and -180 g and +220 g respectively based on the method of Ferrero. It has t o be noted that even greater differences occured: the 10% least exact estim ates deviated by 500 g and more. The difference between estimated and actua l weight increased with the length of pregnancy. The fully trained physicia n (DEGUM II) tended to estimate the birth weight more accurately. The avera ge birth weight estimated sonographically was lower in "DEGUM II-babies" th an that of children whose weight was estimated at the point of admission to the delivery room (Mann-Whitney p < 0,0001). junior doctors showed a tende ncy to over-estimate the birth weight of babies actually being underweight. The opposite happened with babies who presented a relatively higher birth weight: their projected birth weight was underestimated. on the other hand, the regression line of the sonographic estimations of birth weight perform ed by the expert (level II DEGUM) fit to the expected bisector of the angle (Passing-Ba block p > 0,05). Conclusion: When clinical decisions are based on estimated values of birth weight, the possible deviation of this value from the actual weight has to be taken into account. In our study this diff erence came up to 500 g idependent of the level of the examiner's ultrasono graphic training.