BACKGROUND Methods of macrosomic fetal weight estimation are associated with large deviations and statistically significant errors. Fetal macrosomia might be better predicted by using fetal ultrasound measurements and maternal characteristics. METHODS Ultrasound evaluation of fetal weight was performed in 113 singleton fetuses one week (max. 7 days) before delivery. Retrospectively all newborns with birth weight o A new logarithmic estimation formula proposed by Hart and co. was compared with commonly used formulas of Shepard, Campbell, Hadlock I, Hadlock II, Hadlock Ill. Exclusion criteria were: multiple pregnancies, intrauterine deaths, structural or chromosomal abnormalities. The new formula established by Hart (loge EFW = 7.6377445039 + 0.0002951035 x maternal weight + 0.0003949464 x HC + 0.0005241529 x AC + 0,0048698624 x FL) uses fetal biometric measurements and maternal weight as two different parameters: EFW- estimated fetal weight, maternal weight--weight measured at one week (max. 7 days) before delivery HC--fetal head circumference, AC--abdominal circumference, FL--femur length. RESULTS The new Hart formula gives the lowest mean percentage error (MPE) : -0.74% and mean absolute percentage error (MAPE) : 3.38%, as compared to other routinely used formulas which presented statistically significantly higher MPE and AMPE With the new formula 84 of estimated fetal weights fell within +5% of the actual weight at birth, 111 within +/- 10% and 112 within +/- 15% and +/- 20%. CONCLUSIONS The presented ultrasound formula demonstrated a more precise macrosomic fetuses weight estimation with the lowest MPE and MAPE as compared to the others and might be introduced when fetal macrosomia is suspected.