In the present study we investigated the accuracy of Shepard's formula in the sonographic diagnosis of macrosomic fetus of non-diabetic pregnant women. Three hundred and eighty-one macrosomic and 450 appropriate for gestational age (AGA) fetuses born to non-diabetic mothers between 37-42 weeks of gestation were included in the study. Ultrasonographic fetal weight estimation within two days of delivery was made using Shepard's formula in all patients. The estimated fetal weights were compared with the actual birth weights of the same subjects. We did not observe any macrosomic newborn birth in pregnant women with 3200 g or less fetal weight estimation. However, in patients with 3400-3499 g fetal weight estimation, a statistically significant increase in macrosomic newborn birth was observed. Only 3.2% of newborns having actual birth weights greater than or equal to 4000 g had sonographic birth weight estimation less than 4000 g. Accuracy of weight estimations using the Shepard's formula was found to be low in macrosomic fetus. On the other hand, increased incidence of macrosomic newborn birth was observed in subjects with ultrasonographic fetal weight estimations above 3400 g and this level may be useful as a cut-off value for prediction of macrosomic fetus in non-diabetic pregnant women. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.