225 fetuses with ultrasonically determined gestational age were shown by ultrasound to be in breech presentation in the 33rd gestational week. the biparietal diameter (BPD) and the mean of two perpendicular abdominal diameters (AD) were measured ultrasonically in gestational weeks 33, 35, and 38. Based on these measurements, fetal weight was estimated and compared with weight, length, and head circumference at birth and at 18 months of age. 42% of the fetuses were born in breech presentation (breech group) and 58% in vertex presentation (vertex group). the mean birth weight corrected for gestational age was 4.9% lower in the breech group than in the vertex group, which corresponds to the lower intra-uterine values of BPD and AD found in the breech group. the weight differences at birth still persisted at 18 months of age. There were no differences between the groups regarding head circumference or length, either at birth or at 18 months of age.