[Use of ultrasonography to estimate fetal weight in premature infants. Development of a new mathematical formula].

In 73 pregnant patients at a gestational age under 36 weeks, who gave birth within 72 hours from the last US examination, mathematical equations were elaborated. The equations were aimed at predicting fetal weight by measuring the main US biometric parameters; the results were compared to the actual birth weight. A statistical analysis was performed using the "backward elimination" method. The linear equation that has provided with the best estimation of fetal weight is the following: fetal weight = 12.9875 BPD +29.5642 AD +28.8023 FL -3496.1265. According to this equation, about 95.22% of the variability of the unknown quantity (i.e. birth weight) can be ascribed to its correlation to the variables: biparietal diameter (BPD), abdominal diameter (AD) and femur length (FL). Estimated fetal weight by US, as calculated on the basis of biparietal diameter, abdominal diameter and femur length measurements, showed, in our study, a standard error of 143 g (9.02%) (R = 0.95).