[Intrauterine fetal weight assessment using ultrasound. A comparison of several weight assessment methods and development of a new formula for the determination of fetal weight]

Abstract

At the Department of Gynaecology and Obstetrics of the University of Mainz, the foetal weights were estimated in 196 foetuses between 24 and 42 weeks of gestation. All estimates were based on sonographic determination 0-6 days prior to delivery. In a prospective study the equations of Hansmann, Schillinger et al., Campbell and Wilkin, Warsof et al., Shepard et al., Higginbottom et al., Thurnau et al. and an own unpublished formula of Merz were compared. In addition, with the aid of computer analysis, a new equation for predicting foetal weight was evolved from the data measured in this study. This formula should be valid for all weight groups. In 25.5% of the newborn the actual birth weights ranged from 610 to 2499 g, in 42.9% from 2500 to 3499 g and in 31.6% from 3500 to 4520 g. On comparing the individual equations for the entire study group, the most reliable formulas for estimating foetal weights were found to be those of Shepard et al. (72.4%), Hansmann (61.2%) and Merz (61.2%). In the very low birth-weight range less than 2500 g the formula of Shepard et al. proved to be the most reliable for estimating foetal weight with 72%. In the group between 2500 and 3499 g reliability in estimating foetal weight was over 60% with the equations of Shepard et al. (72.6%), Hansmann (67.9%) and Merz (61.9%). In the birth-weight group of 3500 to 4520 g the most reliable formula for predicting foetal weight was found to be that of Schillinger et al. (91.9%), Hansmann (83.9%), Shepard et al. (72.6%) and Merz (69.4%). The formula which was derived from own data was as follows: W (g) = -3200.40479 + 157.07186 AC (cm) + 15.90391 (BPD)2 (cm). With this formula we obtained 71.4% reliability in predicting foetal weight with a mean absolute weight difference of 221 g for the complete study group. Are of validity for this formula could be defined as follows: BPD 7.0-10.5 cm AC 21.8-36.5 cm (all measurements from outer to outer margin).